6 TOPOGEAPHICAL ANATOMY OF 



deep pectoral muscle. Caudally the space is bounded by the latissimus 

 dorsi and cutaneous muscles, while cranially its limits are not very 

 precise, but merge into the triangular interval that corresponds in 

 position to the supraclavicular fossa on the surface of the body. 



V. AXiLLAEis. — The axillary vein is the largest and most ventral 

 vessel now exposed. It forms the continuation of the brachial vein, 

 and, running to the border of the first rib, ends by joining the jugular 

 vein. Its tributaries are the external thoracic, subscapular, and 

 thoraco-acromial veins. 



A. AXILLARIS. — The axillary artery is a continuation of the sub- 

 clavian, and is arbitrarily considered to begin at the border of the 

 first rib. Crossing the axilla obliquely, it ends on a level with the 

 distal border of the teres major muscle, and is continued onwards in 

 the arm by the brachial artery. The branches of the axillary artery 

 are (1) the omocervical trunk ; (2) the external thoracic artery ; (3) the 

 tho7'aco- acromial artery; and (4) the subscapiolar a^'tery. Only the 

 first two demand examination at this stage of the dissection. 



Teuncus omocervicalis. — The omocervical ^ trunk varies greatly 

 in length. Arising from the axillary close to the border of the first 

 rib, it soon divides into two branches. One of these, the ascending 

 cervical artery (a. cervicalis ascendens), turns into the neck between 

 the omohyoid and brachiocephalic muscles, and need not be followed 

 further by the dissector of the limb. 



The other branch of the omocervical trunk is the transverse sca])ular 

 artery (a. transversa scapulae), which lies at first under brachiocephalic 

 and deep pectoral (prescapular part) muscles. It soon gains the lateral 

 pectoral groove, where it has already been found between the brachio- 

 cephalic and superficial pectoral (clavicular part). 



A. THOEACiGA EXTERNA. — The external thoracic artery leaves the 

 caudal border of the axillary close to the first rib. Coursing in a 

 caudal direction along the deep face of the deep pectoral muscle, it 

 supplies this as well as the overlying superficial pectoral. 



V. THOEACiCA EXTERNA. — The so-called external thoracic vein is 

 not, strictly speaking, a satellite of the artery of the same name, 

 though a small branch of the artery may be found alongside the vein 

 in the later part of its course. Beginning underneath the skin in 

 the region of the flank, the vein pierces the cutaneous muscle and 

 gains the lateral border of the deep pectoral muscle, where it is 

 related to the caudal pectoral nerve. Gaining the axilla, where it 

 is often joined by thoracodorsal vein, it generally ends by opening 

 into the axillary vein, but may terminate in the brachial. 



