ANATOMY OF THE DRILL. 



451 



trunk which divides into middle subscapular and circumflex. The 

 musculo-spiral nerve is formed by the posterior division of the 

 conjoined fifth and sixth, the posterior division of the seventh, 

 and the posterior division of the conjoined eighth cervical and first 

 dorsal nerves as in Homo. 



The posterior division of the seventh and the whole of the 

 eighth cervical nerves fuse to form a trunk which divides into 

 median and ulnar nerves. The median has externally only a 

 single head of origin, so it dit.ers from those of Macacus rhesus 

 and Homo, in which two were seen. 



Text-figure 24. 



The lumbo-sacral plexus. S.G. and I.G : superior and inferior gluteal nerves ; 

 Q.F : to quadratus femoris ; G.S : great sciatic ; Sy : sympathetic. 



The long subscapular werfe arises from the back of the musculo- 

 spiral nerve as in some examples of Macacus rhesus (1). And 

 Brooks points out that, although its origin may vary considerably, 

 it is always related in some way to the musculo-spiral. 



The nerves to the pectoral muscles arise from the median nerve, 

 but they may simply run through the latter for a considerable 

 distance. 



In my opinion the musculo- cutaneous nerve represents the 

 outer cord in the human plexus, the posterior cord is represented 

 by the separated circumflex and musculo-spiral nerves, and the 

 inner cord is the band which divides into median and ulnar 

 nerves. It is, however, diflScult to explain how the median and 



