138 Anatomy of the Rabbit. 



**The axillary vein (v. axillaris) begins at the medial side of the 

 humerus and crosses the axillary fossa to the first rib whence it is con- 

 tinued as the subclavian. It receives the lateral thoracic and sub- 

 scapular veins, which accompany the corresponding arteries, and also 

 the cephalic vein (p. 143), which reaches the medial side of the shoulder 

 from the anterior surface of the arm by passing between the teres 

 major and subscapular muscles near the neck of the scapula. 



***The brachial plexus (plexus brachialis) is the network of nerves 

 formed from the ansae of the ventral rami of the posterior five cervical 

 and first thoracic spinal nerves. The cervical ansae also take part in 

 the formation of the more general cervical plexus embracing all nerves 

 of the cervical series. The strands of the brachial plexus cross the 

 axillary fossa and at the medial surface of the humerus are largely re- 

 placed by the three chief trunks of the free extremity, the radial, median, 

 and ulnar nerves (p. 143). The suprascapular nerve (n. suprascapularis) 

 is a large nerve formed from the fifth cervical ansa; it enters the muscle 

 in the region of the neck of the scapula and passing around the 

 superior border of the bone is distributed to the supraspinatus and 

 infraspinatus muscles. The subscapular nerves (nn. subscapulares), 

 arising from the sixth and seventh ansae, are distributed to the subsca- 

 pular, teres major, and latissimus dorsi muscles. 



The axillary lymph glands (lymphoglandulae axillares) are pink or 

 brownish bodies lying in the fat of the axillary fossa. 



4. Muscles arising from the pectoral girdle and inserted on the 

 humerus. These muscles act on the humerus through the shoulder- 

 joint, and except for the unimportant difference in origin are similar to 

 those of Group 2. 



The course of the cephalic vein (p. 143) should be traced before 

 separating the muscles of the front of the forearm. 



Note the supraspinous and infraspinous fasciae covering the corres- 

 ponding portions of the lateral surface of the shoulder. 



(a) The deltoideus. Origin: Lateral portion of the clavicle and 

 the cleidohumeral ligament. Insertion: Anterior surface of 

 the humerus in its distal third. The muscle is a continuation 

 of the basioclavicularis. 



(b) The abductor brachii superior. Origin : The acromion. In- 

 sertion : Distal portion of the humeral spine. 



(c) The abductor brachii inferior. Origin: Infraspinous fascia. 

 The end of the muscle forms a curved line over the dorsal 

 portion of the infraspinatus, leaving only a small triangular 

 portion of the latter exposed. Insertion: The distal portion 

 of the muscle passes beneath the metacromion, which also 

 serves as a point of attachment, and is replaced on the lateral 

 surface of the humerus, beneath the abductor brachii superior, 

 by the long thin tendon, through which it is inserted. 



The abductores are also considered as sesond and third portions of 

 the deltoideus. 



