THE PERICARDIUM

The pericardium is the sac that encloses the heart. It consists of an outer fibrous part known as the fibrous pericardium, and a double layered serous sac known as the serous pericardium.

The fibrous pericardium servers to limit the sudden distention of the heart, it is conical in shape and has an apex and a base, anterior and a posterior surface.

The apex fuses with the roots of the great vessels. It encloses the aorta, superior vena cava, and the pulmonary trunk. Its base fuses with the central tendon of the diaphragm and with some muscular fibres in the left side of the diaphragm. Anteriorly it lies posterior to the body of the sternum, between the 2^nd to 6^th costal cartilages. It is attached superiorly and inferiorly to the body of the sternum by the sterno-pericardial ligament. It is prevented from contact with the anterior thoracic wall by the lungs and pleura except at the lower left part of the sternum and at the sternal end of 4^th to 6^th costal cartilages. Posteriorly it lies anterior to the body of 5^th to 8^th thoracic vertebrae. It is prevented from contact with the vertebrae by the oesophagus, posterior surface of the mediastinal part of the lungs, and the descending thoracic aorta. Laterally it is bounded by the mediastinal pleura, here it is in contact with the phrenic nerves.

The serous pericardium is one of the serous membranes of the body and is similar in structure to the pleura and peritoneum. The serous pericardium has both a parietal layer and a visceral layer. The parietal layer lines the inside of the fibrous pericardium while the visceral layer lines the heart and the vessels entering it. This layer is also known as the epicardium of the heart.

The serous pericardium gives rise to two sheaths – A venous serous sheath and arterial serous sheath. The venous serous sheath encloses the inferior vena cava, the two right pulmonary veins, and the superior vena cava. It then deviates to enclose the two left pulmonary veins. In between the inferior vena cava and left pulmonary vein is a space referred to as the oblique sinus. It presents site for ligation of the veins during cardiac operations. The arterial serous sheath encloses the aorta and the pulmonary trunk. It also has a transverse sinus below it. A double layer of serous membrane separates the two sinuses.

BLOOD SUPPLY

Blood is supplied by branches from the internal thoracic artery, and musculophrenic artery and from the descending aorta. Its venous drainage is from tributaries that empty into the azygous system of veins.

NERVE SUPPLY

It is supplied by branches arising from the vagus, phrenic and sympathetic trunk.

APPLIED ANATOMY

1.                 Pericardiatis: This is a condition whereby the pericardium becomes inflamed. In severe cases it could lead to adhesion of the pericardium to the heart. And this could lead to hypertrophy of the heart since it will require more force or pressure to expand the pericardium.

2.                 Pericardial puncture is carried out close to the medial or sternal end of the 5^th to 6^th costal cartilage near the margin of the sternum to avoid puncture of the internal thoracic artery. It can also be made close to the xyphoid process i.e. left xiphicostal angle; the syringe is passed upwards and backwards to enter the pericardium.

CONTENTS OF THE PERICARDIUM

1.                 Pulmonary trunk

2.                 Ascending aorta

3.                 Terminal end of inferior vena cava and superior vena cava

4.                 Right and left pulmonary veins

5.                 The heart.

PULMONARY TRUNK

The pulmonary trunk is about 5cm in lenght. It begins  in front of the Aorta and passes (semi-spirally) upwards, backwards and to the left until it reaches the concavity  of the arch of Aorta where it bifurcates into the right and left pulmonary arteries.

ASCENDING AORTA

The ascending aorta begins behind the pulmonary trunk and passes obliquely upward, forward and to the right, to reach the right margin to the sternum within the pericardial sac.  Its right wall is dilated and is known as the bulb of the aorta.

AORTA VALUE & PULMONARY VALVE

Both values prevent backflow of blood into the ventricles and both have 3 semilunar values or cups, though the aortic cusps are stronger.

At the root of both arteries, there are 3 dilatations known as sinuses each lies external to each values to prevent it from sticking to the wall of prevent it from the vale is open.

The aorta orifice and the first 5mm to 10mm of the Aorticare filorous and not dilatable so the values remains  competent. The 3 values of the Arotic  value are the right and left, & posterior values. While the pulmonary trunk  has right, left & anternior values.

MEDIASTINUM

The mediastinum is the central partition that lies between the two pleura cavity. Therefore it is covered with the mediastinal pleura. It is bounded anteriorly by the sternum, posteriorly by the body of the second thoracic vertebra, on each side (laterally) by the mediastinal pleura, superiorly by the plane of the thoracic inlet and inferiorly by the plane of the thoracic outlet which is flood in by the diaphragm. The mediastinum contains only small amount of loose connective tissue with space in between the mediastinal structures. It is a highly mobile region.

DIVISION

The mediastinum is divided into two parts by a plane passing behind the manubruosternal joint to the lower border of T4 (in between the intervertebral disc between T4 and T5). The part that lies above is known as the superior mediastinum while the lower part is the inferior mediastinum.

The inferior mediastinum is further divided into three compartments by the fibrous pericardium which includes the anterior, middle and posterior mediastinum by the serous pericardium.

SUPERIOR MEDIASTNUM

It is bounded anteriorly by the manubrum of the sternum and posteriorly by the upper four thoracic vertebrae, on each side is the mediastinal pleura, superiorly by the plane of the thoracic inlet and inferior by the plane passing between the manubrosternal joint and lower border of the fourth thoracic vertebra.

The posterior wall is longer and more concave than the anterior wall therefore it is wedged-shaped.

CONTENTS OF THE SUPERIOR MEDIASTINUM INCLUDE:

1.                 Lower end of the sternohyoid, sternothyroid and longus coli muscles.

2.                 Some of the great veins of the thorax which include; the right and left brachiocephalic vein which are formed by the union of the internal jugular vein and the subclavian vein of the corresponding side, superior vena cava formed by the union of the right and left brachiocephalic vein.

3.                 The arch of the aorta and its three great branches. The left subclavian artery, the right brachiocephalic trunk, and the left common carotid artery.

4.                 Left superior intercostal vein.

5.                 The remnants of the thymus

6.                 The trachea

7.                 Oesophagus

8.                 Thoracic duct

9.                 Tracheobronchial, bronchopulmonary and brachiocephalic lymph nodes

10.             The superficial part of cardiac plexus.

11.             The vagus nerve and left recurrent laryngeal nerve.

12.             The third phrenic nerve.

13.             The right lymphatic trunk.

ANTERIOR MEDIASTINUM

It is bounded between the body of sternum and the anterior wall of the serous pericardium. It narrows above the level of the 4^th costal cartilage, where the two pleura come close to each other at the median plane, below this level the left pleura deviates from the right pleura.

CONTENTS OF ANTERIOR MEDIASTINUM INCLUDE:

1.                 Some loose areolar tissues.

2.                 Few lymphatic vessels.

3.                 Mediastinal branches of the internal thoracic artery.

4.                 The sternopericardial ligament

5.                 Sometimes the thymus especially during the pubertal ages.

THE MIDDLE MEDIASTINUM

It is bounded anteriorly and posteriorly by the fibrous pericardium.

CONTENTS OF THE MIDDLE MEDIASTINUM:

Structures lying within the pericardium include:

1.                 The ascending aorta.

2.                 The pulmonary trunk.

3.                 The superior vena cava.

4.                 Azygous vein as it empties into the superior vena cava.

5.                 Right and left pulmonary veins.

6.                 The heart.

7.                 Thoracic part of the inferior vena cava.

Other structures include:

1.     The right and left phrenic nerve, which is accompanied by pericardiophrenic vessels.

2.     The bifurcated end of the trachea and main bronchus.

3.     The tracheobronchial lymph nodes.

4.     The deep part of the cardiac plexus.

THE POSTERIOR MEDIASTINUM

The posterior mediastinum and the anterior mediastinum are continues superiorly with the superior mediastinum. Its division is more or less descriptive that anatomical. The posterior mediastinum is bounded in front, from above downward, by the bifurcate end of the trachea, the posterior surface of the pericardium and the upper surface of the posterior part of the diaphragm. Posteriorly it is bounded by the bodies of the fifth to twelfth thoracic vertebrae.

CONTENTS OF THE POSTERIOR MEDIASTINUM

1.                 The descending thoracic aorta and its intercostal aortic branches.

2.                 The oesophagus and the anterior and posterior vagus nerve that accompanies it.

3.                 The thoracic duct.

4.                 Azygous system of veins.

5.                 Splanchnic nerve.

6.                 Posterior intercostal lymph nodes.

APPLIED ANATOMY

Mediastinum

The loose space of the neck is in continuity with the mediastinum and it is limited by fascia, the pre-vertebral and pre-tracheal fascia which extends from the neck into the superior mediastinum. The pre-tracheal fascia blends with the arch of the aorta while the pre-vertebral fascia blends with the 4^th thoracic vertebra. Therefore infection occurring anterior to the pre-tracheal fascia spreads downward into the anterior mediastinum while infection occurring posterior to the pre-vertebral fascia is limited to the superior mediastinum between the fascia and the posterior wall. Infection occurring in between the fascia spreads down into the posterior mediastinum.

2.       MEDIASTINAL RADIOLOGY

The anterior posterior radiograph of the mediastinum presents a mediastinal shadow which is created by the heart and the structure passing to and fro it. The structures that from the boundary of the left shadow include the left subclavian artery, the arch of the aorta which is referred to as aortic knuckle by the radiologist, the left auricle and the left pulmonary vein while on the right side are the terminal end of the right brachiocephalic vein, superior vena cava, the right atrium and the thoracic part of the inferior vena cava.

THE LUNG

The lung is the paired principal organ of respiration and it is composed of spongy wall of elastic tissue which feels like a rubber sponge being spongy in nature it floats in water and crepitates when handled, because of air resent in the alveoli.

Location

It is found within the thoracic cavity being separated from each other by the heart and other mediastinal content. It lies within the pleura cavity since it invaginates the pleura from the medial side, it is entirely enclosed by the pleura except at its hilum.

External Features

At birth the lungs is pinkish in colour but in adults it is dark grey in colour and mottled in appearance as a result of deposition of inhaled carbon particles in its surface underneath its loose connective tissue. The surface is shiny and smooth and finely marked into polyhedral surfaces by dark lines and these correspond to the lobules of the lungs.

The Weight

The right lung is about 625g while the left is about 565g. This is when the lung is filled with blood and other serious fluid, when it is empty of blood the right weighs about 240g while the left being smaller weighs even less. But in general the lung of a male weighs higher than the lung of the female.

Shape of the Lung

The lung take the shape of the cavity which it lies therefore it is conical in shape with an apex and a base, three surfaces; a coastal, diaphragmatic and medial surfaces, three borders; an anterior, inferior and posterior borders.

The Apex

It is the part of the lung that extends in to the root of the neck. It is lined by the cervical pleura, which is over lined by a tough membrane known as the suprapleural membrane. This membrane separates it from the subclavian artery and vein which grooves its anterior surface. The apex is about 3 – 4cm above the level of the 1^st intercostal cartilage and it levels with the neck of the 1^st rib posteriorly. It is about 2.5cm above the medial 1/3^rd of the clavicle. Posterior to the apex lies the cervicothoracic sympathetic ganglion.

The Base

It is concave and semilunar in shape. It over lies the superior surface of the diaphragm which separates it on the right from the lobe of the liver, and on the left separates the base of the left lung from the left hepatic lobe of the liver, the fundus of the stomach and the spleen. The doom of diaphragm being higher on the right side than on the left due to the presence of the liver beneath as a result of this the right lung is shorter with a deeper concavity of the base than that of the left lung.

Surfaces:

Costal Surface

It is smooth and convex in shape and overlies the thoracic cage and when fixed insitu (in anatomical position) it bears the marks of the ribs which it overlies. The costal surface is deeper behind than in front and it is lined by the costal pleura.

Diaphragmatic surface

It corresponds to the base of the lungs. It is that part that overlies the diaphragm.

It is concave in shape as it overlies the dome of the diaphragm.

Medial Surface

It is made up of two parts: the vertebral part and the mediastinal surface.

The vertebral part is full and rounded and lies in the paravertebral gutter. It is in contact with the posterior intercostal vessels and nerves and the splanchnic nerve. It corresponds to the posterior border of the lung.

The mediastinal surface is that part that overlies the heart and the pericardial sac and other structures of the mediastinum. It is deeply concave and bears the impress of those structures within the mediastinum which it overlies when fixed insitu. The most prominent of the structure which are found in the mediastinal surface is the hilum of the lung and the line of attachment of the pulmonary ligament.

The impression of the mediastinal surface of the right lung differs from that of the left. In the right lung, anteroinferior to the hilum and pulmonary ligament is a shallow depression known as the cardiac impression which continues superiorly with the groove for the superior vena cava and the terminal right brachiocephalic vein. The groove for superior vena cava is joined from behind by an arching groove above the hilum which lodges the azygous vein. Posterior to the hilum and pulmonary ligament are grooves for the oesophagus and azygous vein. Inferior to the cardiac impression is a shallow groove that lodges in the inferior vena cava.

On the left lung, the cardiac impression which also lies anteroinferior to the pulmonary ligament and hilum is more concave and deeper than that of the right side. Superior to the cardiac impression is a shallow groove that lodges the pulmonary trunk. It is joined by an arching groove which passes above and behind the hilum and the pulmonary ligament. This groove lodges in the aorta. Between the groove for the descending aorta and the pulmonary ligament is a smaller groove formed by the oesophagus, superior to the arching groove of the aorta is the groove for the left subclavian artery and the left brachiocephalic vein. On both lungs it should be noted that the 1^st rib and the subclavian vessels grooved the anterior surfaces.

BORDERS OF THE LUNGS

Anterior Border:

The anterior border are thin and sharp and over laps the pericardium and other mediastinal content on the right lungs the anterior border is more or less vertical and correspond closely to the costomediastinal line of pleura reflection. But on the left the anterior border is only vertical above the attachment of the 4^th costal cartilage. Below this level is present a variable size of cardiac notch which is as a result of the development of the heart at the area of the cardiac notch the pericardium is only covered by a double layer of parietal pleura. It marks the area of superficial cardiac dullness.

Inferior Border:

It is sharp and thin anteriorly where it separates the costal surface from the diaphragmatic surface. It is the part that descends into the costodiaphragmatic recess. Medially where it separates the diaphragmatic surface and mediastinal surface it becomes rounded.

Posterior Border:

It corresponds to the vertebral part of the medial surface of the lungs. It separates the mediastinal surface from the costal surface and it is in contact with the thoracic vertebral and the intervertebral disc between them.

Fissures of the Lungs and Lobes

In the two lungs there is a complete oblique fissure which cut across the costal, diaphragmatic and medial surface. It follows the lines of the 6^th rib and when the arm is raised above the head level it overly the medial border of the scapular. This fissure is higher and more vertical on the left then on the right. But in general they commence 6cm below the apex of the lung, 2cm from the medial plane and at the level of the 3^rd and 4^th spine of the vertebra.

A transverse fissure is present on the right lung which passes transversely along the level of the 4^th rib to meet with the oblique fissure at the mid axillary line as a result of this there is the presence of three lobes in the right lungs which indicates the superior, the middle and inferior lobes.

And on the left lung there is the presence of two lobes the superior lobe and the inferior lobe. But it should be noted that on the anterior inferior part of the superior lobe of the left lung there is the presence of a tongue like process known as the lingular. This lingular process and the cardiac notch correspond to the middle lobe of the right lung.

Root of the Lung

It is formed by structures entering to and fro the hilum and they include the principal bronchus, the pulmonary artery and vein, the pulmonary autonomic plexus, the bronchial arteries and veins, the bronchial pulmonary lymph nodes and lymph vessels and some loose cutaneous tissues. The structures forming the root of the lung is arranged similarly horizontally but vertically the arrangement differs on the right.

The arrangement of the superior bronchus, the pulmonary artery, the pulmonary vein is as follows: On the right, the principal bronchus lies between the pulmonary artery and vein, somehow interposing between the two, but more or less posterior. On the left, it is the pulmonary artery that lies between the principal bronchus and the pulmonary vein.

The tracheal on bifurcation give rise to right and left principal bronchus for the corresponding right and left lung. The right principal bronchus which is more vertical and shorter than the left bronchus, it is about 2.5cm in length and it is the direct continuation of the trachea. As a result of this, foreign bodies that enter the respiratory tract always lodge into the right lung. The right principal bronchus before it enters the right lung, at the level of fifth thoracic vertebra gives off its first secondary bronchus for the superior lobe, as it enters the lung substance; it gives off two other secondary bronchi for the middle lobe and the inferior lobe of the right lung. The superior secondary bronchus gives rise to three segmental bronchi which are named; the anterior, the apical and the posterior segmental bronchus, the secondary bronchus to the middle lobe gives rise to medial and lateral segmental bronchi, the third bronchus for the inferior lobe gives off five segmental bronchi;  an apical, anterior basal, medial basal, posterior basal and lateral basal.

In the left lung, the left principal bronchus is more horizontally placed and longer about 5cm in length. It enters the substance of the lungs and there it divides into two secondary bronchi for the superior and inferior lobe.

The superior lobar bronchus will later divide into a superior division which will give off two segmental bronchi; the anterior and the apicoposterior. The apico-posterior will then divide into the apical and posterior segmental bronchus. The lower division will give off two segmental bronchi, the superior lingular bronchi and the inferior lingular bronchii. The inferior lobar bronchus will give two tertiary bronchi; superior and inferior lingular bronchus. The two lobar bronchi that supply the inferior lobe will give up an apical segmental bronchi and divide into two, one giving the anteromedial bronchus which will later divide into anterior and medial segmental bronchi.

The lower division will give up posterior and lateral segmental bronchus. Therefore there are ten segmental bronchi on the right and eight segmental tertiary bronchi on the left. Each tertiary bronchus and the particular area of lung tissue it supply constitutes the functional unit of the lung known as the bronchopulmonary segment which comprises of one segmental bronchus, a segmental artery which is a branch of pulmonary artery and inter segmental vein which lie in the septum.

THE VESSELS OF THE LUNG

1.                 The pulmonary arteries, they carry deoxygenated blood to the lung for oxygenation and they follow the bronchial tree.

2.                 Pulmonary veins: There are pairs of pulmonary veins on the right and left lung though sometimes in the left it can be three veins and they carry deoxygenated blood back to the left atrium of the heart.

3.                 The bronchial artery and vein are the nutrient supplying vessels of the lungs. They supply the bronchi and other related structures. Sometimes at the capillary level they anastomose with the pulmonary artery and in some rare cases they could replace the pulmonary artery.

LYMPHATIC DRAINAGE

The lymphatic vessels of the lung drain into the bronchopulmonary lymph nodes, which drain into the tracheobronchial group of lymph nodes.

Nerve Supply

The vagus nerve and the upper five sympathetic ganglions give up branches that form the pulmonary plexus which now supplies the lung.

Applied Anatomy

Tuberculosis of the Lung: The apex of the lung is the most prone part that is easily affected by tuberculosis. This is because it is the part that is less ventilated in the lung.

THORACIC CAVITY, PLEURA ,

The thoracic cavity is divided into the right and left pleural cavity which encloses the corresponding right and left lungs. The mediastinum which includes the heart, blood vessel passing through and fro the heart, the structure passing from the neck into the abdomen.

PLEURA

The pleura are serous invaginating sacs made up of an inner visceral layer and outer parietal layer and a connecting part or root.

The visceral pleura is also known as the pulmonary pleura because if encloses tightly the lungs, it encloses all the surface of the lung even extending into its fissures, though it is deficient at the hilum of the lung. The parietal pleura is the outer layer that lines the thoracic cage. It is made up of four parts, they are:

·        costal pleura

·        Diaphragmatic pleura

·        Mediasternal pleura

·        Cervical pleura

The parietal pleura is held into the thoracic cage by a loose areolar tissue known as the endothoracic fascia.

THE COSTAL PLEURA

This is the part of the pleura that line the thoracic wall it overlies the internal surface of the sternum, the transversus thoracis muscle, the ribs and its costal cartilages, the innermost intercostalis muscles and the bodies of the vertebrae and the sides of the vertebrae bodies.

THE DIAPHRAGMATIC PLUERA

This is the part that lines the thoracic surface or the upper surface of the diaphragm.

MEDIASTERNAL PLEURA

This is the part that lines the lateral boundary of the mediastinum.

THE CERVICAL PLEURA

It is the continuation of the costal pleura over the apex of the lung. It ascends from the medial 1/3^rd of the clavicle up to the apex of the lungs, to reach the lateral part of the trachea and here it continues as the mediastinal pleura. The cervical pleura is overlaid by a tough membrane known as the suprapleural membrane.

THE CONNECTION OR ROOT

This is present at the medial aspect of the lung where the mediastinal pleura continues with the visceral pleura. Its upper half is traversed by the root of the lungs while the lower half is empty but for the presence of lymphatic vessels this part is known as the pulmonary ligament.

LINE OF PLEURA REFLECTION

The costal pleural is continuous with the mediastinal pleura anteriorly behind the sternum and posteriorly in front of the vertebral column. The costal pleura is also continues with the diaphragmatic pleura along the costal arches this constitute the sternal and costal reflections. The knowledge of the limit of the sternal and costal reflections is of high clinical importance because it marks the limit of the pleura cavity which will easily be endangered in surgery involving the upper abdominal compact.

To plot the extent of the pleura in the living body, the different even numbers of ribs are taken into consideration or act as a guide this include the 2^nd, 4^th, 6^th, 8^th, 10^th, and the 12^th ribs. The pleura reflection from the apex of the lung the cervical pleura descends anteriorly passing behind the sternoclavicular joint as the sternal reflection now both pleura will descend behind the manubnum to meet each other at the manubrosternal joint which corresponds to the point of articulation of the 2^nd costal cartilage. Both sternal reflections will continue downward close to each other up to the level of the 4^th costal cartilage, here the left sternal reflection will deviate laterally while the right will continue downward up to the back of the xiphoid process.

The left sternal reflection will now descends downward at about 2- 25mm to the lateral edge of the sternum. It will continue its descent up to the 6^th costal cartilage it now starts deviating obliquely crossing the 8^th rib at the midclavicular line, the 10^th rib at the mid axillary line and the 12^th rib at its neck.

From the back of the xiphoid process the right sternal reflection crosses the 7^th costal cartilage, cross the 8^th rib at the midclavicular and thereafter it crosses the 10^th rib at the midaxillary line, similar to the left costal reflection.

The pleura is exposed where it lies beyond the thoracic cage. This is at:

1.                 xiphiscostal angle

2.                 Right costovertebral angle

3.                 Left costverebral angle.

These are the areas where the pleura are in danger of laceration in cases of upper abdominal surgery.

PLEURA CAVITY

This is the potential space lying between the visceral and parietal pleura. The left pleura cavity is smaller than the right this is because of the position of the heart towards the left thoracic cavity. Inside the pleural cavity is a thin layer of fluid known as the pleural fluid which helps in lubrication, allowing the visceral pleura to glide smoothly and soundless over the parietal pleura. It also helps in presenting a high surface tension between the visceral and parietal pleura as a result of this the lungs which adheres to the viscera also adheres to the parietal layer which is also adherent to the thoracic wall, as a result of this an intra thoracic pressure is established and the lungs is perpetually inflated against its elasticity.

The pleura cavity though encloses the lungs but the lung does not fill all the spaces within the pleura cavity, the space within the pleura cavity that is devoid of lungs is known as the pleural recesses.

The size of the pleura recesses is determined by the respiratory activity of the lung. It increases during expiratory process and decreases in inspiratory process.

The three areas where the lung does not fully extend into include:

1.                 Left costomediasternal recess

2.                 Right costodiaphragmatic recess

3.                 Left costodiaphragmatic recess

The left costomediasternal recess lies anterior to the 4^th and 5^th intercostal space at this point the left lung is deficient where it forms a varied cardiac notch as a result of the development of the heart. Here the heart and the pericardium are covered by a double layer of parietal pleura. This marks the area of the superficial cardiac dullness.

The right and left costodiaphramatic recess lies along the corresponding side of the costal arches. At this point the diaphragmatic pleura comes in contact with the costal pleura.

APPLIED ANATOMY

1.                 The visceral pleura always glide over the parietal pleura without any sound or pain. In situation where pain or sounds are experienced. It will be as a result of inflation of the pleura.

2.                 The relation of the pleura to the 12^th rib is of importance during renal surgery this is because the medial border of the kidney lies above it. The pleura crosses the 12^th rib at the lateral border of the muscle rectus spinae in situation where it does not extends beyond the lateral border of rectus spinae the 11^th rib might be mistaken for the 12^th rib and when incision is carried along this 11th rib it will lead to laceration of the pleura cavity unknowingly. To avoid this, the ribs should be counted from the sternal angle where the 2^nd rib is most prominent.

3.                 The intra thoracic pressure and the surface tension created by the pleural fluid maintain the lungs in an inflated position. Anything that disrupt the intra thoracic pressure and the surface tension will automatically lead to the collapse of the lungs. The condition may be as a result of the movement of air or fluid due to pathological conditions or when artificially air is introduced in order to rest the lungs after surgery. In cases where air enters the pleural cavity such condition is known as pneumothorax and it could be of two types:

a.                  Sucking pneumothorax: This condition happens when air enters and leaves the pleural cavity through a gapping wound in the thoracic wall with each respiration. This condition leads to hyperexpansion of the normal side and a condition known as the mediasternal flutter where the content of the mediastinum will shift to the normal side during inspiration and abnormal or injured side during expiration.

b.                 Tension pneumothorax: In this condition air moves into the pleura cavity with inspiration but could not leave during expiration. This condition arises when the penetrating wood act like a valve allowing one way flow of air. In this condition there is hyperexpansion of the thoracic cavity with the mediastinum shifting towards to the normal side. Both conditions do affect the vital capacity of the normal lung thereby affecting the ventilation of the lungs. Pneumothorax can be induced artificially this is normally done to relax the lungs after surgery of the lungs.

4.                 A condition where there is presence of blood in the pleural cavity is known as hemothorax this could be as a result of injury to the large and small vessels of the lungs. A condition where there is fluid in the pleural cavity as a result of direct or indirect pathological conditions like congestive heart failure, inflammation of the pleura such condition is referred to as hydrothorax. When it becomes infected it will result in pus formation within the pleura cavity a condition known as pyothrorax.  When there is accumulation of lymph within the pleura cavity as a result of rapture to the thoracic duct such condition is known as pylothorax. Accumulation of these substances in the pleural cavity reduces the vital capacity of the lungs.

INTERCOSTAL SPACES

The intercostal space is the space lying between two costae (ribs and their costal cartilages) there are about 11 intercostal space and they contain.

1.                 Intercostal muscles.

2.                 Intercostal nerve, artery, and vein.

3.                 Lymphatic vessel.

INTERCOSTAL MUSCLES:

Are made up of layers:

1.                 An External layer which comprises the external intercostal muscle and membrane.

2.                 A middle layer made up of internal intercostal muscle and its membrane.

3.                 An inner most layer which is made up of innermost intercostal muscle also known as intercostal intimi, the transverse thoracic and the subcostalis muscle.

EXTERNAL INTERCOSTAL MUSCLE

Origin: It arises from the lower border of the rib above and runs downward to be inserted into the upper border of the rib below. The fibers run downward and forward corresponding with the pathway of the movement of the hand into the pocket.

Action: Elevation of the rib.

Nerve Supply: They are supplied by intercoastal nerve 1 – 11 each for each space.

INTERNAL INTERCOSTAL MUSCLE

Arises from the costal groove of the rib above inserted into the upper border of the rib below and its fibers are running diagonally downward and backward in opposite direction to the external intercostal muscle.

Nerve supply: Intercoastal nerve 1 – 11 each nerve for its corresponding space.

Action: it depresses the rib in forceful respiration.

INNERMOST INTERCOSTAL MUSCLE

It is more or less functionally part of the internal intercostal muscle. Its fibers run in the same direction as the fibers of the internal intercostal muscle, and it is separated from the internal intercostal muscle by the intercostal vessels. It arises from the posterior part of the costal groove.

Intercostal vessels lies between the inner most intercostal muscle and internal intercostal muscle.

The inner most intercostal muscle sometimes extends from its space to other spaces. It does not have intercostal membrane. It is only limited to the lateral wall of the thorax.

Subcostalis it cross more than one space, they are much more developed at the upper spaces.

Transverse thoracis muscle, it arises from the posterior surface of the xiphoid process and the posterior surface of the lower part of the body of the sternum It then fans out to be inserted into the 6^th,5^th, 4^th, 3^rd and 2^nd rib, and the corresponding costal cartilage. It is supplied by the T2 – T6 intercostal nerves.

TYPICAL INTERCOSTAL NERVE must have:

1.       Lateral cutaneous nerve which divides into anterior and posterior ramus.

2.       Anterior cutaneous nerve which divides into medial and lateral cutaneous branch.

3.       It must lie within the intercostal space.

4.       It must supply structure within its space.

CLASSIFICATION OF INTERCOSTALNERVE

·        Intercostal nerve 1 and 2 are atypical because they give off a greater branch that forms part of the brachial plexus. They also give off cutaneous contribution to the upper limb. Intercostal nerve two has lateral cutaneous nerve but lack anterior and posterior rami, the lateral cutaneous branch is known as intercostobrachial nerve.

·        Intercostal nerves 3 to 6 are typical intercostal nerves with all the basic features.

·        Intercostal nerves T7 to T11 have all the features of typical intercostal nerve with the exception that they all cross their corresponding spaces to supply the anterior abdominal wall.

A TYPICAL INTERCOSTAL SPACE

This is a space that contains a typical nerve, rib and vertebra. The spaces between the 3^rd – 5^th ribs are typical spaces. Within each space lie one posterior intercostal artery and two anterior intercostal arteries, making 11 posterior intercostal arteries and 22 anterior intercostal arteries in the eleven intercostal spaces.

THE INTRINSIC MUSCLES OF THE HAND

The intrinsic muscles of the hand serve the function of adjusting the hand during gripping and also for carrying out fined skilled movements. There are twenty muscles in the hand, they are as follow:

Thenar eminence:

There are three muscles that form the thenar eminence with a common origin from the flexor retinaculum. The fourth muscle that is related to the thenar muscles is the adductor pollicis which have a different origin. The thenar muscles include: 

ABDUCTOR POLLICI BREVIS

Origin: Flexor retinaculum, tubercle of scaphoid and tubercle of trapezium.

Insertion: Is inserted into the radial side of the base of the proximal phalanx of the thumb. Some fibers are inserted into the dorsal digital expansion.

Nerve Supply: Median nerve

Action: Abduction and medial rotation of the thumb at the metacarpophalangeal joint and carpometacarpal joint. 

FLEXOR POLLICIS BREVIS:

It is related to the ulnar side of abductor pollicis brevis.

Origin: It arises by a superficial head from the flexor retinaculum and the tubercle of trapezium and by a deep head from the trapezoid and capitate, sometimes this head is absent in some individuals.

Insertion: It is inserted in to the radial sesamoid of the thumb and on the radial side of the base of proximal phalanx.

Nerve Supply: Superficial head is supplied by the median nerve and the deep head by the deep branch of ulnar nerve.

Action: Flexion of the thumb at the proximal phalanx.

OPPONENS POLLICIS:

 It lies deep to the flexor pollicis brevis and abductor pollicis brevis muscles.

Origin: It arises from the tubercle of trapezium and flexion retinaculum.

Insertion: Lateral half of the palmar surface of the 1^st metacarpal bone.

Nerve Supply: Median nerve

Action: Opposition of the thumb.

ADDUCTION POLLICIS:

Origin: It arises by means of two heads, an oblique head which arises from the capitate bone and the base of the 2^nd and 3^rd metacarpal bones and a transverse head which arises from the palmar aspect of the 3^rd metacarpal bone.

Insertion: Medial side of the base of the proximal phalanx of the thumb and some fibres are inserted into the dorsal digital expansion.

Nerve Supply: Deep branch of the ulnar nerve (C8T1)

Action: The muscle adducts the thumb from the flexed or abducted position. The movement is forceful in gripping.

HYPOTHENAR EMINENCE

It is the muscles that lie on the ulnar side of the palm similar to the thenar muscle. They are four in number and include:

ABDUCTOR DIGITI MINIMI

This is the most medial of the group.

Origin: It arises from the pisiform bone and the tendon of flexor carpi ulnaris proximally and from the pisohamate ligament distally.

Insertion:  Ulnar side of the base of the proximal phalanx o f the little finger.

Nerve Supply: Deep branch of ulnar nerve.

Action: Abduction of little finger at the metacarpophalangeal joint.

FLEXOR DIGITI MINIMI BREVIS

Origin: Arises from the hook of hamate bone and flexor retinaculum.

Insertion: Ulnar side of the base of the proximal phalanx of the little finger.

Nerve Supply: Deep branch of ulnar nerve (C8 T1).

Action: Flexion of the little finger at the metacarpophalangeal joint.

OPPONENS DIGITI MINIMI

Origin: It arises from the flexor retinaculum and hook of hamate.

Insertion: Medial surface of the shaft of the 5^th metacarpal bone.

Nerve Supply: Deep branch of ulnar nerve (C8 T1).

Action: Flexes of 5^th metacarpal and rotate it laterally.

LUMBRICAL MUSCLES

These are four small muscles that take origin from the tendon of flexor digitorum profundus and passes along the radial side of the corresponding metacarpophalangeal joint on the palmar surface of the deep transverse metacarpal ligament to be inserted by a tendon into the extensor expansion of the dorsum of the medial four digits.

Origin: The 1^st lumbrical arises from the radial side of the tendon for the index finger. The 2^nd lumbrical arises from the radial side of the tendon for the middle finger. The 3^rd lumbrical arises from the contiguous sides of the tendon of the middle and ring finger. The 4^th lumbrical arises from the contiguous side of the tendon for the ring and little finger.

Insertion: The tendons of the 1^st, 2^nd, 3^rd, and 4^th lumbrical pass backward on the radial side of the 2^nd, 3^rd, 4^th, and 5^th metacarpophalangeal joints respectively. They are inserted into the dorsal expansion of the corresponding digits.

Nerve Supply:

1.                 The 1^st and 2^nd lumbrical muscles by the median nerve (C8, T1).

2.                 The 3^rd and 4^th lumbrical muscles by the deep branch of ulnar nerve.

Action: The lumbrical muscles flex the metacarpophalangeal joints and extend the interphalangeal joints of the digit into which they are inserted.

INTEROSSEOUS MUSCLE

They are of two groups, the palmar and dorsal interossei. The former are small and arises from only one metacarpal bone while the latter are large and arise from the adjacent metacarpal bone of the space in which they lie. It is easy to recall the action of the interosseous by a appreciating their format “PAD and DAB”.

PALMAR INTEROSSEI

They are numbered from lateral to medial side.

Origin:

·        The 1^st palmar interosseous muscle arises from the medial side of the base of the 1^st metacarpal bone.

·        The 2^nd palmar interosseous arises from the medial half of the palmar aspect of the shaft  of the 2^nd metacarpal.

·        The 3^rd palmar interosseous arises from the lateral part of the palmar surface of the shaft of the 4^th metacarpal bone.

·        The 4^th palmar interosseous from the lateral part of the palmar aspect of the shaft of the 5^th metacarpal bone.

Insertion: Each muscle is inserted into the dorsal digital expansion of its own digit. It may also be attached to the base of the proximal phalanx of the same digit.

1.                 1^st palmar interosseous muscle inserts into the medial side of the thumb.

2.                 2^nd palmar interosseous muscle inserts into the medial side of the index finger.

3.                 3^rd palmar interosseous muscle inserts into the lateral side of the fourth digit.

4.                 4^th palmar interosseous muscle inserts into the lateral side of the 5^th digit.

The middle finger does not receive the insertion of the palmar interossei.

Nerve Supply: They are all supplied by the deep branch of the ulnar nerve.

Action: They adduct (PAD) the digit to which they are attached toward the middle finger. In addition they flex the digit at the metacarpophalangeal joints and extend it at the interphalangeal joints.

THE DORSAL INTEROSSEI

They are also four in number and placed between the metacarpal bones and are numbered from lateral to medial.

Origin:

i.                    1^st dorsal interosseous muscle arises from the shaft of the 1^st and 2^nd metacarpal.

ii.                  2^nd dorsal interosseous muscle arises from the shaft of the 2^nd and 3^rd metacarpal.

iii.                3^rd dorsal interosseous muscle arises from the shaft of the 3^rd and 4^th metacarpal.

iv.               4^th dorsal interosseous muscle arises from the shaft of the 4^th and 5^th metacarpal.

Insertion: Each muscle is inserted in to the dorsal digital exp of the digits and into the base of the proximal phalanx of the digit.

1^stdorsal interosseous muscle inserts into the lateral side of index finger

2^nd dorsal interosseous muscle inserts into the lateral side of middle finger

3^rd dorsal interosseous muscle inserts into the medial side of middle finger

4^th dorsal interosseous muscle inserts into the medial side of 4^th digit

It should be noted that the middle finger receives two dorsal interossei muscles on either side and that the 1^st and 5^th digit do not receive any insertion.

Action: All dorsal interossei abduct the digit away from the line of the middle finger.

Nerve supply: By the deep branch of the ulnar nerve.

APPLIED ANATOMY

Paralysis of the intrinsic muscle of the hand produces claw hand in which there is hyperextension at the metacarpophalangeal joint and flexion at the interphalangeal joint. The effect is opposite to the action of the lumbricals and interossei.

HAND

The hand is designed purposely, normally universal digit formula 3>4>2>5>1 (for man and apes)

Another digit formula for the whites

3>4=2>5>1    19% Caucasians

3>2>4>5>1>         33% Caucasians

axial line: Pass through the capitate through the metacarpal the 3^rd digit.

PALM

Furrows and ridges increase the surface area and increase the force of gripping. Sebaceous gland is absent but sweat glands are present. Furrow and ridges are arranged into arches whorls.

Palmar aponeurosis it is found in the central part of the palm and is a triangular deep fascia formed due to degeneration of the palmaris longus muscle tendon. It has an apex which is attached to the flexor retinaculum, its base divides into 

F                        our slips.

The intrinsic muscles of the hand serve the function of adjusting the hand during gripping and also for carrying out fined skilled movements. There are twenty muscles in the hand, they are as follow:

Thenar eminence:

There are three muscles that form the thenar eminence with a common origin from the flexor retinaculum. The fourth muscle that is related to the thenar muscles is the adductor pollicis which have a different origin. The thenar muscles include: 

ABDUCTOR POLLICI BREVIS

Origin: Flexor retinaculum, tubercle of scaphoid and tubercle of trapezium.

Insertion: Is inserted into the radial side of the base of the proximal phalanx of the thumb. Some fibers are inserted into the dorsal digital expansion.

Nerve Supply: Median nerve

Action: Abduction and medial rotation of the thumb at the metacarpophalangeal joint and carpometacarpal joint. 

FLEXOR POLLICIS BREVIS:

It is related to the ulnar side of abductor pollicis brevis.

Origin: It arises by a superficial head from the flexor retinaculum and the tubercle of trapezium and by a deep head from the trapezoid and capitate, sometimes this head is absent in some individuals.

Insertion: It is inserted in to the radial sesamoid of the thumb and on the radial side of the base of proximal phalanx.

Nerve Supply: Superficial head is supplied by the median nerve and the deep head by the deep branch of ulnar nerve.

Action: Flexion of the thumb at the proximal phalanx.

OPPONENS POLLICIS:

 It lies deep to the flexor pollicis brevis and abductor pollicis brevis muscles.

Origin: It arises from the tubercle of trapezium and flexion retinaculum.

Insertion: Lateral half of the palmar surface of the 1^st metacarpal bone.

Nerve Supply: Median nerve

Action: Opposition of the thumb.

ADDUCTION POLLICIS:

Origin: It arises by means of two heads, an oblique head which arises from the capitate bone and the base of the 2^nd and 3^rd metacarpal bones and a transverse head which arises from the palmar aspect of the 3^rd metacarpal bone.

Insertion: Medial side of the base of the proximal phalanx of the thumb and some fibres are inserted into the dorsal digital expansion.

Nerve Supply: Deep branch of the ulnar nerve (C8T1)

Action: The muscle adducts the thumb from the flexed or abducted position. The movement is forceful in gripping.

HYPOTHENAR EMINENCE

It is the muscles that lie on the ulnar side of the palm similar to the thenar muscle. They are four in number and include:

ABDUCTOR DIGITI MINIMI

This is the most medial of the group.

Origin: It arises from the pisiform bone and the tendon of flexor carpi ulnaris proximally and from the pisohamate ligament distally.

Insertion:  Ulnar side of the base of the proximal phalanx o f the little finger.

Nerve Supply: Deep branch of ulnar nerve.

Action: Abduction of little finger at the metacarpophalangeal joint.

FLEXOR DIGITI MINIMI BREVIS

Origin: Arises from the hook of hamate bone and flexor retinaculum.

Insertion: Ulnar side of the base of the proximal phalanx of the little finger.

Nerve Supply: Deep branch of ulnar nerve (C8 T1).

Action: Flexion of the little finger at the metacarpophalangeal joint.

OPPONENS DIGITI MINIMI

Origin: It arises from the flexor retinaculum and hook of hamate.

Insertion: Medial surface of the shaft of the 5^th metacarpal bone.

Nerve Supply: Deep branch of ulnar nerve (C8 T1).

Action: Flexes of 5^th metacarpal and rotate it laterally.

LUMBRICAL MUSCLES

These are four small muscles that take origin from the tendon of flexor digitorum profundus and passes along the radial side of the corresponding metacarpophalangeal joint on the palmar surface of the deep transverse metacarpal ligament to be inserted by a tendon into the extensor expansion of the dorsum of the medial four digits.

Origin: The 1^st lumbrical arises from the radial side of the tendon for the index finger. The 2^nd lumbrical arises from the radial side of the tendon for the middle finger. The 3^rd lumbrical arises from the contiguous sides of the tendon of the middle and ring finger. The 4^th lumbrical arises from the contiguous side of the tendon for the ring and little finger.

Insertion: The tendons of the 1^st, 2^nd, 3^rd, and 4^th lumbrical pass backward on the radial side of the 2^nd, 3^rd, 4^th, and 5^th metacarpophalangeal joints respectively. They are inserted into the dorsal expansion of the corresponding digits.

Nerve Supply:

1.                 The 1^st and 2^nd lumbrical muscles by the median nerve (C8, T1).

2.                 The 3^rd and 4^th lumbrical muscles by the deep branch of ulnar nerve.

Action: The lumbrical muscles flex the metacarpophalangeal joints and extend the interphalangeal joints of the digit into which they are inserted.

INTEROSSEOUS MUSCLE

They are of two groups, the palmar and dorsal interossei. The former are small and arises from only one metacarpal bone while the latter are large and arise from the adjacent metacarpal bone of the space in which they lie. It is easy to recall the action of the interosseous by a appreciating their format “PAD and DAB”.

PALMAR INTEROSSEI

They are numbered from lateral to medial side.

Origin:

·        The 1^st palmar interosseous muscle arises from the medial side of the base of the 1^st metacarpal bone.

·        The 2^nd palmar interosseous arises from the medial half of the palmar aspect of the shaft  of the 2^nd metacarpal.

·        The 3^rd palmar interosseous arises from the lateral part of the palmar surface of the shaft of the 4^th metacarpal bone.

·        The 4^th palmar interosseous from the lateral part of the palmar aspect of the shaft of the 5^th metacarpal bone.

Insertion: Each muscle is inserted into the dorsal digital expansion of its own digit. It may also be attached to the base of the proximal phalanx of the same digit.

1.                 1^st palmar interosseous muscle inserts into the medial side of the thumb.

2.                 2^nd palmar interosseous muscle inserts into the medial side of the index finger.

3.                 3^rd palmar interosseous muscle inserts into the lateral side of the fourth digit.

4.                 4^th palmar interosseous muscle inserts into the lateral side of the 5^th digit.

The middle finger does not receive the insertion of the palmar interossei.

Nerve Supply: They are all supplied by the deep branch of the ulnar nerve.

Action: They adduct (PAD) the digit to which they are attached toward the middle finger. In addition they flex the digit at the metacarpophalangeal joints and extend it at the interphalangeal joints.

THE DORSAL INTEROSSEI

They are also four in number and placed between the metacarpal bones and are numbered from lateral to medial.

Origin:

i.                    1^st dorsal interosseous muscle arises from the shaft of the 1^st and 2^nd metacarpal.

ii.                  2^nd dorsal interosseous muscle arises from the shaft of the 2^nd and 3^rd metacarpal.

iii.                3^rd dorsal interosseous muscle arises from the shaft of the 3^rd and 4^th metacarpal.

iv.               4^th dorsal interosseous muscle arises from the shaft of the 4^th and 5^th metacarpal.

Insertion: Each muscle is inserted in to the dorsal digital exp of the digits and into the base of the proximal phalanx of the digit.

1^stdorsal interosseous muscle inserts into the lateral side of index finger

2^nd dorsal interosseous muscle inserts into the lateral side of middle finger

3^rd dorsal interosseous muscle inserts into the medial side of middle finger

4^th dorsal interosseous muscle inserts into the medial side of 4^th digit

It should be noted that the middle finger receives two dorsal interossei muscles on either side and that the 1^st and 5^th digit do not receive any insertion.

Action: All dorsal interossei abduct the digit away from the line of the middle finger.

Nerve supply: By the deep branch of the ulnar nerve.

APPLIED ANATOMY

Paralysis of the intrinsic muscle of the hand produces claw hand in which there is hyperextension at the metacarpophalangeal joint and flexion at the interphalangeal joint. The effect is opposite to the action of the lumbricals and interossei.

HAND

The hand is designed purposely, normally universal digit formula 3>4>2>5>1 (for man and apes)

Another digit formula for the whites

3>4=2>5>1    19% Caucasians

3>2>4>5>1>         33% Caucasians

axial line: Pass through the capitate through the metacarpal the 3^rd digit.

PALM

Furrows and ridges increase the surface area and increase the force of gripping. Sebaceous gland is absent but sweat glands are present. Furrow and ridges are arranged into arches whorls.

Palmar aponeurosis it is found in the central part of the palm and is a triangular deep fascia formed due to degeneration of the palmaris longus muscle tendon. It has an apex which is attached to the flexor retinaculum, its base divides into 

F                        our slips.

The intrinsic muscles of the hand serve the function of adjusting the hand during gripping and also for carrying out fined skilled movements. There are twenty muscles in the hand, they are as follow:

Thenar eminence:

There are three muscles that form the thenar eminence with a common origin from the flexor retinaculum. The fourth muscle that is related to the thenar muscles is the adductor pollicis which have a different origin. The thenar muscles include: 

ABDUCTOR POLLICI BREVIS

Origin: Flexor retinaculum, tubercle of scaphoid and tubercle of trapezium.

Insertion: Is inserted into the radial side of the base of the proximal phalanx of the thumb. Some fibers are inserted into the dorsal digital expansion.

Nerve Supply: Median nerve

Action: Abduction and medial rotation of the thumb at the metacarpophalangeal joint and carpometacarpal joint. 

FLEXOR POLLICIS BREVIS:

It is related to the ulnar side of abductor pollicis brevis.

Origin: It arises by a superficial head from the flexor retinaculum and the tubercle of trapezium and by a deep head from the trapezoid and capitate, sometimes this head is absent in some individuals.

Insertion: It is inserted in to the radial sesamoid of the thumb and on the radial side of the base of proximal phalanx.

Nerve Supply: Superficial head is supplied by the median nerve and the deep head by the deep branch of ulnar nerve.

Action: Flexion of the thumb at the proximal phalanx.

OPPONENS POLLICIS:

 It lies deep to the flexor pollicis brevis and abductor pollicis brevis muscles.

Origin: It arises from the tubercle of trapezium and flexion retinaculum.

Insertion: Lateral half of the palmar surface of the 1^st metacarpal bone.

Nerve Supply: Median nerve

Action: Opposition of the thumb.

ADDUCTION POLLICIS:

Origin: It arises by means of two heads, an oblique head which arises from the capitate bone and the base of the 2^nd and 3^rd metacarpal bones and a transverse head which arises from the palmar aspect of the 3^rd metacarpal bone.

Insertion: Medial side of the base of the proximal phalanx of the thumb and some fibres are inserted into the dorsal digital expansion.

Nerve Supply: Deep branch of the ulnar nerve (C8T1)

Action: The muscle adducts the thumb from the flexed or abducted position. The movement is forceful in gripping.

HYPOTHENAR EMINENCE

It is the muscles that lie on the ulnar side of the palm similar to the thenar muscle. They are four in number and include:

ABDUCTOR DIGITI MINIMI

This is the most medial of the group.

Origin: It arises from the pisiform bone and the tendon of flexor carpi ulnaris proximally and from the pisohamate ligament distally.

Insertion:  Ulnar side of the base of the proximal phalanx o f the little finger.

Nerve Supply: Deep branch of ulnar nerve.

Action: Abduction of little finger at the metacarpophalangeal joint.

FLEXOR DIGITI MINIMI BREVIS

Origin: Arises from the hook of hamate bone and flexor retinaculum.

Insertion: Ulnar side of the base of the proximal phalanx of the little finger.

Nerve Supply: Deep branch of ulnar nerve (C8 T1).

Action: Flexion of the little finger at the metacarpophalangeal joint.

OPPONENS DIGITI MINIMI

Origin: It arises from the flexor retinaculum and hook of hamate.

Insertion: Medial surface of the shaft of the 5^th metacarpal bone.

Nerve Supply: Deep branch of ulnar nerve (C8 T1).

Action: Flexes of 5^th metacarpal and rotate it laterally.

LUMBRICAL MUSCLES

These are four small muscles that take origin from the tendon of flexor digitorum profundus and passes along the radial side of the corresponding metacarpophalangeal joint on the palmar surface of the deep transverse metacarpal ligament to be inserted by a tendon into the extensor expansion of the dorsum of the medial four digits.

Origin: The 1^st lumbrical arises from the radial side of the tendon for the index finger. The 2^nd lumbrical arises from the radial side of the tendon for the middle finger. The 3^rd lumbrical arises from the contiguous sides of the tendon of the middle and ring finger. The 4^th lumbrical arises from the contiguous side of the tendon for the ring and little finger.

Insertion: The tendons of the 1^st, 2^nd, 3^rd, and 4^th lumbrical pass backward on the radial side of the 2^nd, 3^rd, 4^th, and 5^th metacarpophalangeal joints respectively. They are inserted into the dorsal expansion of the corresponding digits.

Nerve Supply:

1.                 The 1^st and 2^nd lumbrical muscles by the median nerve (C8, T1).

2.                 The 3^rd and 4^th lumbrical muscles by the deep branch of ulnar nerve.

Action: The lumbrical muscles flex the metacarpophalangeal joints and extend the interphalangeal joints of the digit into which they are inserted.

INTEROSSEOUS MUSCLE

They are of two groups, the palmar and dorsal interossei. The former are small and arises from only one metacarpal bone while the latter are large and arise from the adjacent metacarpal bone of the space in which they lie. It is easy to recall the action of the interosseous by a appreciating their format “PAD and DAB”.

PALMAR INTEROSSEI

They are numbered from lateral to medial side.

Origin:

·        The 1^st palmar interosseous muscle arises from the medial side of the base of the 1^st metacarpal bone.

·        The 2^nd palmar interosseous arises from the medial half of the palmar aspect of the shaft  of the 2^nd metacarpal.

·        The 3^rd palmar interosseous arises from the lateral part of the palmar surface of the shaft of the 4^th metacarpal bone.

·        The 4^th palmar interosseous from the lateral part of the palmar aspect of the shaft of the 5^th metacarpal bone.

Insertion: Each muscle is inserted into the dorsal digital expansion of its own digit. It may also be attached to the base of the proximal phalanx of the same digit.

1.                 1^st palmar interosseous muscle inserts into the medial side of the thumb.

2.                 2^nd palmar interosseous muscle inserts into the medial side of the index finger.

3.                 3^rd palmar interosseous muscle inserts into the lateral side of the fourth digit.

4.                 4^th palmar interosseous muscle inserts into the lateral side of the 5^th digit.

The middle finger does not receive the insertion of the palmar interossei.

Nerve Supply: They are all supplied by the deep branch of the ulnar nerve.

Action: They adduct (PAD) the digit to which they are attached toward the middle finger. In addition they flex the digit at the metacarpophalangeal joints and extend it at the interphalangeal joints.

THE DORSAL INTEROSSEI

They are also four in number and placed between the metacarpal bones and are numbered from lateral to medial.

Origin:

i.                    1^st dorsal interosseous muscle arises from the shaft of the 1^st and 2^nd metacarpal.

ii.                  2^nd dorsal interosseous muscle arises from the shaft of the 2^nd and 3^rd metacarpal.

iii.                3^rd dorsal interosseous muscle arises from the shaft of the 3^rd and 4^th metacarpal.

iv.               4^th dorsal interosseous muscle arises from the shaft of the 4^th and 5^th metacarpal.

Insertion: Each muscle is inserted in to the dorsal digital exp of the digits and into the base of the proximal phalanx of the digit.

1^stdorsal interosseous muscle inserts into the lateral side of index finger

2^nd dorsal interosseous muscle inserts into the lateral side of middle finger

3^rd dorsal interosseous muscle inserts into the medial side of middle finger

4^th dorsal interosseous muscle inserts into the medial side of 4^th digit

It should be noted that the middle finger receives two dorsal interossei muscles on either side and that the 1^st and 5^th digit do not receive any insertion.

Action: All dorsal interossei abduct the digit away from the line of the middle finger.

Nerve supply: By the deep branch of the ulnar nerve.

APPLIED ANATOMY

Paralysis of the intrinsic muscle of the hand produces claw hand in which there is hyperextension at the metacarpophalangeal joint and flexion at the interphalangeal joint. The effect is opposite to the action of the lumbricals and interossei.

HAND

The hand is designed purposely, normally universal digit formula 3>4>2>5>1 (for man and apes)

Another digit formula for the whites

3>4=2>5>1    19% Caucasians

3>2>4>5>1>         33% Caucasians

axial line: Pass through the capitate through the metacarpal the 3^rd digit.

PALM

Furrows and ridges increase the surface area and increase the force of gripping. Sebaceous gland is absent but sweat glands are present. Furrow and ridges are arranged into arches whorls.

Palmar aponeurosis it is found in the central part of the palm and is a triangular deep fascia formed due to degeneration of the palmaris longus muscle tendon. It has an apex which is attached to the flexor retinaculum, its base divides into 

F                        our slips.