210 Anatomy of the Rabbit. 



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

 nerves formed from the ventral rami of the posterior five cervical 

 and first thoracic spinal nerves. The cervical nerves 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 replaced by the three chief trunks of the tree extremity, 

 the radial, median, and ulnar nerves. These nerves are formed 

 principally from the eighth cervical, but adjacent nerves also 

 contribute, especially a large bundle which enters the radial from 

 the seventh cervical, from which combined trunk the stout sub- 

 scapular nerves are given off to the corresponding muscle. A 

 suprascapular nerve, formed chiefly from the sixth cervical, 

 passes to the anterior border of the scapula, entering the supra- 

 spinatus muscle. 



By dividing the axillary nerves and vessels and the two parts of the serratus 

 anterior muscle, the limb may be removed from the body. 



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. 216) should be traced before 

 separating the muscles of the front of the forearm. 



Note the supraspinous and infraspinous fasciae cover- 

 ing the corresponding portions of the lateral surface of the 

 shoulder. 



(a) The cleidohumeralis. 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, but represents the 

 brachial part of the brachiocephalic muscle, which, in 

 many mammals with reduced clavicle, extends from the 

 mastoid portion of the skull to the front of the arm. The 

 cervical part is the cleidomastoideus. 



