236 ELEMENTS OF MAMMALIAN ANATOMY 



branch to the first thoracic nerve, is continued as the main part 

 of the muscuh)spiral nerve. 



The first thoracic nerve gives first a large branch to the mus- 

 culospiral nerve, a second small branch to the anterior thoracic, 

 and a third branch forming the internal cutaneous nerve supply- 

 ing the skin of the arm and forearm on the caudal aspect. The 

 main portion of the first thoracic nerve then continues as the 

 main part of the ulnar nerve. 



The nerves of the forelimb are five in number (Fig. 114) : the 

 external cutaneous or musculo-cutaneous, the internal cuta- 

 neous, the musculospiral, the median, and the ulnar. The 

 external cutaneous arises from the sixth and seventh cervical 

 nerves and passes distad along the caudal aspect to the biceps 

 to the cranial aspect of the forearm, where it becomes subcutane- 

 ous. It supplies the biceps and coracoid muscles and the skin 

 of the forearm. The internal cutaneous arises from the first 

 thoracic and passes along the ventral side of the arm, becoming 

 subcutaneous just proximad of the elbow, where it is distributed 

 to the skin of the arm and forearm on the cadual and ventral 

 aspects. 



The musculospiral (radialis) arises from the seventh and 

 eighth cervical and first thoracic nerves. It is the largest 

 component of the brachial plexus. It winds obliquely around 

 the humerus to the cranial aspect, where it divides into two 

 branches, the radial and the posterior interosseous. The 

 superficial radial nerve is the smaller and becomes subcutaneous 

 near the elbow, and passes along the radial region. The 

 posterior (dorsal) interosseous proceeds along the dorsal aspect 

 of the forearm to the wrist, where it divides into branches 

 supplying the digits. 



The median nerve arises from the seventh and eighth cervical 

 and first thoracic. It follows the course of the brachial artery, 

 passing through the supracondylar forearm to the elbow, where 

 it passes beneath the pronator teres to the carpal region, and 

 supplies the first, second, and third digits. It also supplies the 

 pronator teres and flexor muscles of the forearm. 



