Part 71

a. =A. tibialis recurrens.=--Immediately after passing through the interosseous membrane the anterior tibial sends a small artery proximad to the knee-joint.

b. =Rami musculares.=--Numerous short branches throughout the course of the artery, to the muscles about it.

c. =Ramus superficialis.=--A larger branch leaves the lateral surface of the artery about one-third the distance from the knee to the ankle and passes along with the superficial peroneal nerve, at first beneath M. peroneus longus, then superficially. It passes onto the dorsal surface of the foot and becomes connected with terminal branches of =A. saphena=.

d. =A. tarsea medialis.=--This arises from the tibialis anterior just distad of the transverse ligament through which it passes at the ankle, passes over the medial surface of the astragalus, and is distributed to the ligaments about the ankle-joint. It anastomoses with the plantar branch of A. saphena.

e. =A. metatarsea.=--The metatarsal artery passes laterad from the tibialis anterior at the distal boundary of the tarsus, on the dorsal surface of the foot. It sends branches distad in the intervals between the third and fourth and the fourth and fifth metatarsals.

The distal branches (Fig. 128) of the tibialis anterior have been described in the general description of the artery.

THE VEINS. VENÆ.

=Venæ pulmonales. The Pulmonary Veins.=

The pulmonary veins follow in the lungs the course of the bronchi. They enter the left auricle in three groups (Fig. 116, page 276). The first of these (i) comes from the anterior and middle lobes of the right side, the second (h) from the corresponding lobes of the left side, and the third (g) from the terminal lobes of both sides. Each group is composed of two or three veins and opens into a sinus or extension of the auricle. The sinuses are from their position dextral (i), sinistral (h), and dorsal (g).

=The Veins of the Body.=

The veins of the body may be classified into three main groups: (1) the veins of the heart; (2) the superior vena cava and its branches; (3) the inferior vena cava and its branches. The portal system of veins will be considered with the inferior vena cava.

1. Veins of the Heart.

The veins of the heart consist of one large vein, the =vena cordis magna=, and a number of small veins.

=Vena cordis magna= (Fig. 118, 3).--This arises as a number of scattered branches on the surface of both ventricles. These unite to form two main trunks. One of these, on the ventral side of the heart, marks externally the septum between the two ventricles. It passes beneath the left auricular appendage, then turns to the left and passes along the sulcus coronarius to the dorsal side of the heart. Here it unites with the second main trunk which ramifies over the surface of the left ventricle. Arriving at the base of the right auricle it enters this by the coronary sinus, which lies just beneath the opening of the inferior vena cava.

In addition to the vena cordis magna and its branches there are a number of small veins, especially in the wall of the right ventricle. These enter the right auricle by a number of small separate openings along the sulcus coronarius.

2. =Vena cava superior= (Fig. 129, b).

The superior vena cava is the great vein returning the blood from the head, fore-limb, and cranial part of the trunk. It extends from the level of the first rib on the right side of the vertebral column to the right auricle. Its caudal end lies dorsad of the aortic arch. Opposite the right rib it is formed by the junction of the two innominate veins (m).

Branches of the superior vena cava:

1. =V. azygos= (d).--The first branch of the superior vena cava is the azygos vein, which enters the vena cava on the right side a centimeter or less craniad of the root of the right lung. It is formed in the abdominal cavity by the confluence of two or three small veins, which collect the blood from the muscles of the dorsal wall of the abdomen. The small median trunk thus formed enters the thoracic cavity between the crura of the diaphragm and lies on the ventral surface of the centra of the thoracic vertebræ, slightly to the right of the middle line. The azygos receives the =intercostal= veins (n), which correspond to the intercostal arteries and have the same course and distribution. In the caudal part of the thoracic cavity the intercostals enter the azygos separately, but the intercostals of the cranial intercostal spaces usually unite two or three together and enter the azygos by one or more common trunks. The azygos also receives =bronchial= and =œsophageal= veins, corresponding to the similarly named arteries.

a, aorta; b, vena cava superior; c, vena cava inferior; d, V. azygos; e, A. subclavia dextra; f, A. mammaria interna; g, V. mammaria interna; h, costocervical axis; i, united trunk of vertebral and costocervical veins; j, A. and V. axillaris; k, V. jugularis externa; l, V. jugularis interna; m, the two innominate veins; n, intercostal arteries and veins; o, thyrocervical axis. 1, heart; 2, trachea; 3, œsophagus; I-XI, cut ends of the first eleven ribs.]

2. =V. mammaria interna= (g).--The internal mammary veins follow the corresponding arteries. The two veins unite to form a common trunk which, after receiving a branch from the cranial part of the sternum, enters the vena cava opposite the third rib.

3. =Vv. anonymæ= (Fig. 129, m; Fig. 115, p).--The innominate veins unite opposite the first intercostal space to form the vena cava superior. Each extends from the cranial end of the vena cava superior craniolaterad to a point a short distance craniad of the first rib and is there formed by the union of the =external jugular= (Fig. 129, k) and =subclavian= (j) veins. The innominate vein has the following branches:

A and B. =Vv. vertebralis= and =costocervicalis= (i).--The vertebral and costocervical veins unite to form a single trunk which enters the innominate about opposite the first rib. These two veins follow the corresponding arteries. (Sometimes the vertebral and costocervical veins enter the innominate separately, and in other cases one or more of the components of the costocervical veins (e.g., the transversa colli) may enter the axillary vein. In other cases the entire common trunk of the vertebralis and costocervicalis may enter the superior vena cava directly.)

C. =V. subclavia.=--The subclavian vein enters the innominate at about the level of the first rib. Outside of the thorax it is called the axillary vein (j); this comes from the arm.

SUPERFICIAL ARTERIES, VEINS, AND NERVES ON THE EXTENSOR SIDE OF THE ARM AND DORSUM OF THE HAND.

a, V. cephalica; b, V. mediana cubiti; c, V. cephalica antibrachii; d, A. collateralis radialis superior; e, Aa. and Vv. digitales dorsales; f, A. radialis; g, superficial radial nerve; h, N. musculocutaneus; i, N. cutaneus medialis.]

=Veins of the Arm.=--The blood is returned from the arm by two systems of veins,--a deep and a superficial system.

The deep system is composed of veins which correspond to the branches of the axillary artery, follow in general the same course, and receive the same names (Fig. 122). They unite to form the axillary vein. The brachial vein does not pass with the brachial artery through the supracondyloid foramen.