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 free 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. 
