CIRCULATORY SYSTEM. 215 



of their respective arteries. One of them, apart from the others, 

 is connected with the humeral by a separate canal, and makes 

 a curve upon the inner part of the elbow-joint in the direction of 

 the olecranon, and afterwards descends upon the side of that 

 projection along the backs of the flexors, where it becomes 

 superficial, and continues so to its termination at the knee. 

 The others all end by one common trunk in the humeral vein, 

 about its middle. 



The humeral vein, the issue of the union of the anasto- 

 motic branch from the superficial brachial with the radial veins, 

 is a large vessel extending along the inner side of the humerus, 

 in contact with the bone. The humeral artery, which accom- 

 panies this vessel, is at first concealed between the bone and 

 the vein, but higher up the. artery gets in front of the vein. It 

 receives small veins from the joint, and divers others from the 

 muscles around, whose number is indeterminable, and whose 

 course is best learnt by a reference to that of the arteries. It 

 also receives a considerable branch from the triceps. 



The axillary vein is the continuation of the humeral, 

 augmented by the accession of the triceps vein. The axillary 

 artery enters the limb directly opposite to the shoulder-joint, 

 and the vein runs immediately below and in company with it. 

 It follows the future course of the artery, turning along with it 

 around the first rib, to join the vena cava anterior, which it 

 does at the same place that vessel receives the jugular. Its 

 branches are — I. The suhscapidai' vein, one of considerable 

 size accompanying the subscapular artery, receives as it runs 

 along branches from the triceps and subscapulars, correspond- 

 ing to the arteries, and joins either the root of the axillary or 

 the termination of the humeral. 2. The dorsalis scapulcc pur- 

 sues the course of the artery of that name, bi inging blood from 

 the antea and postea spinati, and terminating about midway 

 between the thorax and shoulder. The remaining branches of the 

 axillary come from the parietes of the thorax. They are — r/. 

 The humeral thoracic, comprising two or three veins, correspond- 

 ing to the arteries so called, the original ramifications of which 

 issue from the muscles about the point of the shoulder, h. The 

 external thoracic, a long vein traversing the lower part of the 

 chest, in a horizontal direction, behind the arm. A great por- 

 tion of it runs subcutaneously, and is distinctly traceable in the 

 living animal through the skin ; from which circumstance it has 

 been noticed by horsemen, and named, from its situation, the spur 

 vein. It is originally derived from the abdominal parietes, from 

 the union of two convergent branches which issue from the 

 integuments of the sheath, or, in the female, the mammae: it 



