450 DR. <^- I'- SONNTAG OX THE 



and the {)lexus is formed l)y the fifth ctei'vical to first doisal 

 inchisive. 



Tlie fourth nerve communicates witli tlie fiftli and becomes the 

 suprnscapular nerve, and the phrenic nerve arises from the 

 junction of the fourth and communicating branches. Filainents 

 may run from the communicating twigs from the cervical plexus 

 to suprascapular and pln-enic nerves. In Macaciis rhesus, 

 according to Brooks (1), the large fourth cervical gives a branch 

 which joins the smnll fifth cervical just as the latter gives off the 

 phrenic nerve. In Homo the phrenic nerve receives definite fibres 

 from the third, fourth, and fifth cervical nerves, and the supra- 

 scapular nerve arises from the fifth and sixth cervicals. 



The fifth, sixth, and seventh nerves quickly divide into anterior 

 and posterior divisions, but the eighth does not divide. So there 



Text-fimire 23. 



The hracliial plexus. The three small fibres running up from C.it are known in 

 the text as C.C.P. The two small twigs attached to the median nerve are the 

 anterior thoracics. C: communicating nerves; C.B : coraco-brachialis ; B.B : 

 biceps : B.A.B : brachialis anticus ; R.N : radial nerve ; P.I : posterior inter- 

 osseous nerve. 



is no trace of trunks as seen in Homo, and there is no upper trunk 

 as in Macacus rhesus. 



The anterior division of the fifth nerve gives off the upper and 

 middle subscapular nerves, and unites with the anterior division 

 of the sixth to form the musculo-cutaneous and middle subscapular 

 nerves. In Macacus rhesus two small subscapulars come from the 

 posterior division of the upper trunk (C.v and C.vi). It is 

 possible that the musculo-cutaneous is the only lepresentative of 

 the outer cord of the plexus in Homo. 



The posterior branches of the fifth and sixth nerves can be 

 traced into the musculo-spiral and circumflex nerves, and the 

 musculo-spiral nerve is joined by the anterior division of the 

 seventh. In Macacus rhesus the posterior of the upper trunk 

 unites with a branch of the seventh cervical nerve to form a 



