366 ABRAM T. KERR 



THE THORACODORSAL NERVE 



The thoracodorsal (middle or long subscapular) nerve is usually 

 described as arising from the posterior fasciculus of the plexus. 



In my series of 161 satisfactory records for this nerve it arises 

 singly from the posterior fasciculus in 93 instances or 57.76 

 per cent (fig. 2). In 2 of these the posterior fasciculus receives 

 no fibers from the first thoracic nerve. In 4 of the above, in 

 addition to its origin from the posterior fasciculus, the nerve 

 has a second root, coming from the dorsal division of the caudal 

 trunk in 2, from the dorsal division of the intermediate trunk in 

 one, and from the posterior fasciculus itself in one. 



In 7 cases the nerve arises from thie posterior fasciculus by a 

 stem common to it and the axillary subscapular nerve. In 9 

 plexuses the nerve arises from the radial nerve which in 5 of 

 these is one of the terminal divisions of the posterior fasciculus 

 and in 3 others the radial nerve is formed by a branch from 

 the trunk produced by the union of the dorsal divisions of the 

 cephalic and intermediate trunks after giving off the axillary 

 nerve joining the dorsal division of the caudal trunk. In another 

 case the radial nerve from which the thoracodorsal arises is formed 

 by a branch from the dorsal division of the cephalic trunk, after 

 giving off the axillary nerve, joining the cord formed by the 

 union of the dorsal division of the intermediate trunk and a 

 dorsal branch of the eighth cervical and joined by a branch from 

 the caudal trunk (fig. 28). 



In 9 plexuses the nerve arises from the axillary nerve. In 8 

 of these this is one of the terminal divisions of the posterior 

 fasciculus (fig. 17). In the other case the axillary nerve comes 

 from the trunk formed by the union of the dorsal branches of the 

 cephalic and intermediate trunks but the thoracodorsal nerve 

 receives almost immediately after its origin from the axillary a 

 branch from the dorsal division of the caudal trunk. 



The thoracodorsal nerve arises either directly or indirectly 

 from the posterior fasciculus of the plexus in 113 plexuses, or in 

 70.19 per cent. 



In 18 instances the thoracodorsal nerve arises from the cord 

 formed by the union of the dorsal divisions of the cephalic and 



