THE NERVOUS SYSTEM. 209 



centimeters from their origin (Fig. 47). The manner in 

 which the nerves anastomose varies somewhat, but the fol- 

 lowing will be found approximately correct: 



The sixth cervical nerve gives off a small branch to the 

 rhomboideus and levator anguli muscles of the shoulder, 

 and then divides into two nearly equal branches, one of 

 which supplies the muscles on the lateral aspect of the 

 scapula, and the other joins with the seventh cervical nerve. 

 Small branches from the fifth and sixth cervical nerves 

 unite to form the phrenic nerve supplying the diaphragm. 



The seventh cervical nerve gives off three small branches 

 at about the same point, one of which is the posterior 

 thoracic supplying the serratus magnus muscle, a second 

 helps to form the musculocutaneous, and the third forms 

 part of the median and anterior thoracic. The main por- 

 tion of the seventh cervical unites with the eighth and first 

 thoracic, to form the musculospiral nerve. The circumflex 

 and subscapular branches supplying the deltoid and sub- 

 scapular muscles are also derived from the seventh. 



The eighth cervical nerve, after giving off a small branch 

 to the pectoral muscle, a small twig to the median nerve, 

 and a large branch to the first thoracic nerve, is continued 

 as the main part of the musculospiral nerve. 



The first thoracic nerve gives first a large branch to the 

 musculospiral nerve, a second small branch to the anterior 

 thoracic, and a third branch forming the internal cutaneous 

 nerve supplying 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. 

 105) : the external cutaneous or musculo-cutaneous, the in- 

 ternal cutaneous, the musculospiral, the median, and the ul- 

 nar. The external cutaneous arises from the sixth and 

 seventh cervical nerves and passes distad along the caudal 

 19 



