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Anterior tibial artery Extensor

(7) The lateral anterior malleolar branch, more constant and larger than the medial, passes laterally, posterior to the extensor digitorum longus and peronæus tertius, towards the lateral malleolus. It anastomoses with the perforating branch of the peroneal artery and with the tarsal artery, and supplies the ankle-joint and the adjacent articulations.

Dorsalis Pedis Artery.—The dorsal artery of the foot is the direct continuation of the anterior tibial; it commences opposite the front of the ankle-joint, and extends to the posterior extremity of the first interosseous space, where it

Perohaus brevis divides into the first dorsal Extensor digitorum

hallucis metatarsal and the pro

longus

longus funda branch.

Tibialis anterior It is covered super

Anterior peroneal

artery ficially by skin and fascia, Lateral malleolar

malleolar artery

artery including the cruciate ligament, and it is crossed, just before it reaches the first interosseous space, by the tendon of the extensor hallucis brevis. It rests upon the anterior Extensor

Dorsalis pedis digitorum ligament of the ankle, the

artery brevis head of the talus, the talonavicular ligament, the Tarsal artery dorsum of the navicular bone, and the dorsal naviculo-cuneiform and the inter-cuneiform ligaments between the first

ist dorsal and second cuneiform artery

metatarsal

artery bones. On its lateral side is the medial terminal Dorsal

inetatarsal branch of the deep peronæal nerve (O.T. anterior tibial), which intervenes between it and the extensor digitorum brevis and most medial tendon of the extensor digitorum longus. On its medial side it is in relation with the tendon of the extensor hallucis longus. Two venæ comites, one on each side, accompany the artery.

Branches. — On the Fig. 784.—THE DORSALIS PEDIS ARTERY AND ITS BRANCHES. dorsum of the foot the dorsalis pedis artery gives off cutaneous branches, lateral and medial tarsal branches, the arcuate branch, and the first dorsal metatarsal and the profunda branch.

(1) Cutaneous branches, two or three in number, are distributed to the skin on the dorsum and medial side of the foot; they anastomose with branches of the medial plantar artery.

(2) The tarsal branches, medial and lateral.—The medial tarsal branches are small vessels given off from the medial side of the artery. They pass to the medial border of the foot and anastomose with branches of the medial plantar artery. The lateral tarsa) branch is given off opposite the head of the talus ; it runs laterally, deep to the extensor hallucis brevis and the extensor digitorum brevis, supplying those muscles and the tarsal joints, and it anastomoses with the perforating branch of the peroneal, the arcuate, and lateral plantar arteries, and with the lateral malleolar artery.

[graphic]

which it goes.

(3) The arcuate artery arises opposite the first cuneiform bone. It runs laterally, on the bases of the metatarsal bones, deep to the long and short extensor tendons, supplies the extensor hallucis brevis and the extensor digitorum brevis, and anastomoses with branches of the lateral tarsal and lateral plantar arteries. It gives off three dorsal metatarsal arteries, second, third, and fourth, which run forwards on the muscles which occupy the three lateral interosseous spaces to the clefts of the toes, where each divides into two dorsal digital branches for the adjacent sides of the toes bounding the cleft to

The lateral side of the little toe receives a branch from the most lateral dorsal metatarsal artery. Each dorsal metatarsal artery gives off a posterior perforating branch, which passes through the posterior part of the intermetatarsal space, between the heads of the dorsal interosseous muscle, to anastomose with the plantar arch, and an anterior perforating branch, which passes through the anterior part of the space to anastomose with the corresponding plantar metatarsal artery.

(4) The first dorsal metatarsal artery is continued forwards from the dorsal artery of the foot, and runs on the dorsal surface of the first dorsal interosseous muscle. It ends by dividing into dorsal digital branches for the adjacent sides of the first and second toes. Before it divides it usually gives off a dorsal digital branch which passes, deep to the tendon of the extensor hallucis, to the medial side of the great toe.

(5) The profunda branch passes through the posterior end of the first intermetatarsal space, between the two heads of the first dorsal interosseous muscle, to the plantar aspect of the foot, where it unites with the lateral plantar artery and completes the plantar arch. As it unites with the lateral plantar artery it gives off the first plantar metatarsal artery (0.T. arteria magna hallucis), which passes forwards, along the first intermetatarsal space, to the base of the first interdigital cleft, where it divides into plantar digital arterie for the adjacent sides of the great and second toes; before it divides it gives off a plantar digital artery to the medial side of the great toe.

VENÆ.

Veins commence at the terminations of the capillaries. They converge towards the heart, and unite with one another to form larger and still larger vessels, until, finally, seven large trunks are formed which open into the atria of the heart. Three of the trunks, the superior vena cava, the inferior vena cava, and the coronary sinus, belong to the systemic circulation; they contain venous blood, and open into the right atrium. The remaining four, the pulmonary veins, belong to the pulmonary circulation; they return oxygenated blood from the lungs, and open into the left atrium.

In addition to the systemic and pulmonary veins, there is also a third group of veins, constituting the portal system, in which blood from the abdominal part of the alimentary canal, and from the spleen and pancreas, is conveyed to the liver. The portal system is further peculiar in that it both begins and ends in capillaries From its terminal capillaries in the liver the hepatic veins arise, and as these open into the inferior vena cava the blood of the portal system is finally poured into the general systemic circulation. The hepatic veins also receive blood supplied to the liver by the hepatic arteries.

VENÆ PULMONALES.

The terminal pulmonary veins (Figs. 750 and 757), two on each side, open into the left atrium of the heart. Their tributaries arise in capillary plexuses in the walls of the pulmonary alveoli. By the union of the smaller veins larger vessels are formed which run along the anterior aspects of the bronchial tubes, and, uniting together, ultimately form a single efferent vessel in each lobe, which passes into the root of the lung. Thus there are five main pulmonary veins, but, immediately after entering the root of the lung, the vessels from the upper and middle lobes of the right lung join together, and so only four terminal pulmonary veins open into the left atrium of the heart. Neither the main stems nor their tributaries possess valves.

Relations. In the root of the lung the upper pulmonary vein, on each side, lies below and in front of the pulmonary artery. The lower pulmonary vein, op each

side, is in the lowest part of the root, and it is in a plane posterior to that in which the upper

vein lies. On the right side the upper pulmonary vein passes behind to the superior vena cava, and the lower passes behind the right atrium. They both terminate in the upper and posterior part of the left atrium close to the interatrial septum.

On the left side both upper and lower pulmonary veins cross anterior to the descending aorta, and they terminate in the upper and posterior part of the left atrium near its left border.

All four pulmonary veins perforate the fibrous layer of the pericardium, and receive partial coverings of the serous layer before they enter the atrium.

SYSTEMIC VEINS.

The systemic veins return blood to the right atrium of the heart through the superior vena cava, the inferior vena cava, and the coronary sinus. The two firstnamed receive blood from the veins of the body and limbs and from most of the abdominal and pelvic viscera. The coronary sinus receives blood from the veins of the walls of the heart alone.

General Arrangement.—The veins of the body wall and limbs form two groups -(1) the superficial veins; (2) the deep veins.

The superficial veins lie in the superficial fascia; they commence in the capillaries of the skin and subcutaneous tissues, and are very numerous. They frequently anastomose with one another, and they also communicate with the deep veins, in which, after piercing the deep fascia, they terminate. They may or may not accompany superficial arteries.

The deep veins accompany arteries, and are known as vence comites. The large arteries have only one accompanying vein, but with the medium-sized and small arteries there are usually two venæ comites, which anastomose freely with each other by short transverse branches of communication.

Visceral veins usually accompany the arteries which supply viscera in the head, neck, thorax, and abdomen. As a rule there is only one vein with each visceral artery, and, with the exception of those which enter into the formation of the portal system, they terminate in the deep systemic veins.

SINUS CORONARIUS ET VENÆ CORDIS. The coronary sinus (Fig. 750) is a short, but relatively wide, venous trunk which receives the majority of the veins of the heart. It lies in the inferior 1 portion of the coronary sulcus, between the left atrium and the left ventricle, and it is covered superficially by some of the muscular fibres of the atrium.

It terminates in the lower and posterior part of the right atrium, between the orifice of the inferior vena cava on the right, and the right atrio-ventricular orifice anteriorly; an imperfect valve, consisting of one cusp, called the valve of the coronary sinus (Thebesius), is situated at the right margin of the opening of the sinus into the atrium.

The apertures of the tributaries of the coronary sinus, except those of the great and small cardiac veins, are not provided with valves, and the valves of the two veins mentioned are often incompetent.

Tributaries.-(1) The great cardiac vein (Fig. 754) commences at the apex of the heart. It ascends, in the anterior interventricular sulcus, to the coronary sulcus; it then turns to the left, and, passing round the left margin of the heart, into the inferior part of the coronary sulcus, terminates in the left extremity of the coronary sinus. It receives tributaries from the walls of both ventricles and from the wall of the left atrium. It receives also the left marginal vein ; that vein commences at the lower extremity of the left margin of the heart, along which it ascends to its termination.

(2) The small cardiac vein is very variable; as a rule it commences at the inferior margin of the heart and passes to the right to the coronary sulcus in which it turns to the left, on the inferior surface of the heart, and terminates in the right extremity of the coronary sinus. It receives tributaries from the walls of the right atrium and the right ventricle.

(3) The oblique vein of the left atrium (Marshall) (Fig. 750) is a small venous channel which descends obliquely, on the posterior wall of the left atrium, and terminates in the coronary sinus. Its orifice is not provided with a valve. It is of special interest, inasmuch as it represents the left superior vena cava of some other mammals, and is developed from the left duct of Cuvier.

(4) The inferior cardiac vein of the left ventricle runs along the inferior surface of the left ventricle and ends in the coronary sinus.

(5) The middle cardiac vein commences at the apex of the heart, and, passing posteriorly, in the inferior interventricular sulcus, terminates in the coronary sinus near its right extremity. It receives tributaries from the inferior parts of the walls of both ventricles.

Veins of the Heart which do not end in the Coronary Sinus.--(a) The anterior cardiac veins are two or three small vessels which ascend on the anterior wall of the right ventricle to the coronary sulcus, where they either end in the right atrium or terminate in the small cardiac vein. (6) The venæ minimæ cordis.—A number of small veins, which commence in the substance of the walls of the heart and terminate directly in its cavities, principally in the atria ; some few, however, open into the ventricles.

VENA CAVA SUPERIOR AND ITS TRIBUTARIES.

The superior vena cava (Figs. 756 and 757) returns the blood from the head and neck, the upper extremities, the thoracic wall

, and a portion of the upper part of the wall of the abdomen. It is formed, at the lower border of the first right costal cartilage, by the union of the two innominate veins, and it descends, with a slight convexity to the right, to the level of the third right costal cartilage, where it opens into the upper and posterior part of the right atrium. It is about 75 mm. (three inches) long; in the lower half of its extent it is enclosed within the fibrous layer of the pericardium, and it is covered in front and on each side by the serous layer.

Relations. It is overlapped anteriorly by the margins of the right lung and pleural sac and by the ascending aorta. The lung and pleura intervene between it and the second and third costal cartilages, the internal intercostal muscles in the first and second intercostal spaces, and the internal mammary vessels. It is in relation posteriorly with the right margin of the trachea, the right vagus nerve, the vena azygos, which opens into it at right angles, the right bronchus, the right pulmonary artery, and the upper right pulmonary vein. On its left side are the ascending portion of the aorta, and the commencement of the innominate artery, whilst on the right side it is in close relation with the right pleura, the phrenic nerve and the pericardiaco-phrenic (O.T. comes nervi phrenici) vessels intervening.

Tributaries.-In addition to the two innominate veins, by the union of which it is formed, the superior vena cava receives only one large tributary, viz., the vena azygos ; but several small pericardial and mediastinal veins open into it

VENA AZYGOS AND ITS TRIBUTARIES. The vena azygos (O.T. vena azygos major) (Fig. 798) commences either from the posterior aspect of the inferior vena cava, at the level of the right renal vein, or as the direct upward continuation, of an anastomosing channel which connects together the lumbar veins of the right side, and which is known as the right ascending lumbar vein. It ascends through the aortic orifice of the diaphragm, and is continued upwards through the posterior mediastinum. In the upper part of its course, it first passes posterior to the root of the right lung, and then arches anteriorly, above the root, to its termination in the posterior part of the superior vena cava, immediately before the latter vessel pierces the pericardium and at the level of the second costal cartilage. It frequently possesses imperfect valves.

Relations.--In the abdomen it lies on the anterior surfaces of the bodies of the upper lumbar vertebræ, posterior to the right crus of the diaphragm and the inferior vena cava, and to the right side of the cisterna chyli.

In the thorax it lies on the anterior surfaces of the bodies of the lower eight thoracic verte bræ, the intervening fibro-cartilages, and the anterior longitudinal ligament; and anterior to

the right aortic intercostal arteries. In the lower part of the posterior mediastinum the right pleura and lung lie anterior to it; at a higher level it is overlapped by the right margin of the wsophagus, and immediately before its termination it is crossed by the root of the right lung.

On its left side it is in relation, in the greater part of its extent, with the thoracic duct and, as it arches anteriorly over the root of the lung, with the right vagus nerve and the trachea. About the level of the eighth thoracic vertebra it receives the accessory hemiazygos vein, whilst at the level of the ninth thoracic vertebra the hemiazygos vein opens into it.

In addition to the two veins last mentioned it receives the right posterior intercostal veins, except that from the first space but including the right superior intercostal vein, the right subcostal vein, and, through the ascending lumbar vein, the upper right lumbar veins. It also receives the right bronchial veins and some small æsophageal, pericardial, and mediastinal tributaries.

Tributaries. — (1) The vena hemiazygos accessoria (0.T. vena azygos minor superior) is formed by the union of the fourth, fifth, sixth, seventh and eighth left posterior intercostal veins. It lies on the left sides of the bodies of the fifth, sixth, and seventh thoracic vertebræ, and the corresponding intercostal arteries. It crosses the vertebral column, from left to right, opposite the body of the eighth thoracic vertebra, passing posterior to the aorta, æsophagus, and thoracic duct; and it terminates either in the vena azygos or in the vena hemiazygos. In addition to its intercostal tributaries it receives the left bronchial veins, and some small posterior mediastinal veins, and it communicates with the left superior intercostal vein.

(2) The vena hemiazygos commences in the epigastric region of the abdomen. At its origin it is connected either with the left ascending lumbar vein or with the left renal vein. After piercing the left crus of the diaphragm it ascends, on the left sides of the bodies of the lower thoracic vertebræ, and, opposite the eighth or ninth thoracic vertebra, it turns to the right, crosses the front of the vertebral column, posterior to the aorta, esophagus, and thoracic duct, and terminates in the vena azygos. As it ascends, on the bodies of the vertebræ, it lies lateral to the aorta, and medial to the roots of the splanchnic nerves, and anterior to the lower left intercostal arteries. Through the left ascending lumbar vein it receives blood from the upper lumbar veins of the left side; the left subcostal vein, the lower three posterior intercostal veins, and small mediastinal tributaries also terminate in it.

(3) The bronchial veins do not quite correspond to the bronchial arteries, and they are not found on the walls of the smallest bronchi. On each side the tributaries run, anterior or posterior to the bronchial tubes to reach the root of the lung, where they unite, as a rule, into two small trunks; those of the right side open into the vena azygos, and those of the left into the accessory hemiazygos vein, or into the left superior intercostal vein.

On both sides they are joined by tracheal and posterior mediastinal veins. Some few small bronchial veins, including most of those from the smaller tubes, open into the pulmonary veins.

(4) Venæ Intercostales.—There are two sets of intercostal veins, the anterior and the posterior.

The anterior intercostal veins are tributaries of the internal mammary or of the musculo-phrenic veins, and are described with those vessels (pp. 962, 963).

The posterior intercostal veins (Fig. 798) are eleven in number on each side. A single vein runs in each intercostal space ; it is situated in the costal groove, above the corresponding artery.

On the right side the posterior intercostal vein of the first space accompanies the superior intercostal artery across the front of the neck of the first rib, and terminates in the vertebral or innominate vein. The second, third, and fourth posterior intercostal

veins of the right side unite together to form a common trunk, the right superior - intercostal vein, which terminates by joining the vena azygos.

The fifth to the eleventh posterior intercostal veins of the right side open separately into the vena azygos.

On the left side the first posterior intercostal vein follows a course similar to that taken by the corresponding vein on the right side, and terminates in the left vertebral or innominate vein. The second, third, and sometimes the fourth posterior intercostal veins of the left side unite to form the left superior intercostal vein, which runs from behind forwards along the left or anterior aspect of the aortic arch. It passes obliquely between the left vagus and phrenic nerves, crosses the root of the left subclavian artery, and ends in the lower border of the left innominate vein. The fifth, sixth, seventh, and eighth, and sometimes the fourth posterior intercostal veins of the left side terminate in the accessory hemiazygos vein, and the ninth, tenth, and eleventh end in the hemiazygos vein

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