914 THE VASCULAE SYSTEM. 



thoracic nerves, and terminate in the subcutaneous tissues and skin of the middle portion of the 

 anterior abdominal wall. 



(iii.) Xiphoid, a small branch which crosses the front of the xiphoid process to anastomose 

 with its fellow of the opposite side. It supplies the adjacent muscles and skin. 



(iv.) Hepatic branches of small size pass backwards in the falciform ligament to the liver, 

 where they anastomose with branches of the hepatic artery. 



(4) Truncus Costocervicalis. The costo-cervical trunk (Fig. *761) springs 

 from the posterior aspect of the second part of the subclavian artery on the right 

 side and from the first part on the left side. It runs upwards and backwards, 

 over the apex of the pleural sac, to the neck of the first rib, where it divides 

 into superior intercostal and deep cervical branches. 



Branches. (a) Arteria Cervicalis Profunda The deep cervical branch sometimes 

 arises from the subclavian artery directly ; but more commonly it springs from the costo- 

 cervical trunk at the upper border of the neck of the first rib. It runs backwards, to the 

 back of the neck, passing between the first thoracic and last cervical nerves, and between 

 the transverse process of the last cervical vertebra and the neck of the first rib. In the 

 back of the neck it ascends, between the semispinalis capitis (O.T. complexus) and the 

 sernispinalis cervicis muscles and it terminates by anastomosing with the descending branch 

 of the occipital artery. It anastomoses also with branches of the ascending cervical and 

 vertebral arteries, supplies the adjacent muscles, and sends a spinal branch, through the 

 intervertebral foramen between the last cervical and the first thoracic vertebra, into the 

 vertebral canal ; this branch anastomoses with the spinal branches of the vertebral and 

 intercostal arteries. 



(6) Arteria Intercostalis Suprema. The superior intercostal branch descends, anterior 

 to the neck of the first rib, between the first thoracic nerve laterally and the first thoracic 

 ganglion of the sympathetic trunk medially and, at the lower border of the neck -of the rib, 

 it gives off the posterior intercostal artery of the first space ; then, after crossing anterior 

 to the neck of the second rib, it becomes the posterior intercostal artery of the second inter- 

 costal space. The first two posterior intercostal arteries, which are respectively a branch 

 and the continuation of the superior intercostal artery, run laterally, each in its own space, 

 lying first between the pleura and the posterior intercostal membrane, and then between 

 the internal and external intercostal muscles. Their branches terminate by anastomosing 

 with anterior intercostal branches of the internal mammary artery. Each gives off 

 muscular branches to the intercostal muscles, a nutrient branch to the rib below which 

 it lies, and a collateral branch which runs along the lower border of the corresponding space. 



ARTERIA AXILLARIS. 



The axillary artery, which lies in the axillary space, is the direct continuation 

 of the subclavian artery, and it becomes the brachial artery. 



It commences at the external border of the first rib, at the apex of the axillary 

 space. It passes distally, with a lateral inclination, along the lateral wall of the 

 space, i.e. to the medial side of the shoulder-joint and the humerus, to the lowei 

 border of the teres major, where it becomes the brachial artery. A line drawi 

 from the middle of the clavicle to the medial border of the prominence of th< 

 coracobrachialis muscle, when the arm is abducted until it is at right angles witl 

 the side, indicates the position and direction of the artery. 



The position and direction, however, and to a certain extent the relations o 

 the axillary artery, are modified by changes in the position of the uppe 

 extremity. With the arm hanging by the side the axillary artery describes ; 

 curve with the concavity directed downwards and medially, and the vein is to it 

 medial side. When the arm is at right angles with the side, the axillary arter 

 is almost straight; it lies closer to the lateral wall of the axilla, and the veil 

 overlaps it antero- medially. When the arm is raised above the level of th 

 shoulder the axillary artery is curved over the head of the humerus, with th 

 convexity of the curve below, and the vein lies still more in front of it. 



For descriptive purposes the artery is divided into three parts : the first pai 

 lies above, the second behind, and the third part below the pectoralis minor. 



Though it is the usual custom to describe three parts of the axillary arter 

 a division which is of practical interest in so far as it emphasises the fact thc r 

 the axillary artery is surgically accessible above the pectoralis minor, it is to I 



