CHAP. IV] THE GENERAL ANATOMY OF THE CERCOPITHECIDAE 143 



In studying the peripheral nerves of the Cercopithecidae, we 

 encounter again evidence (as in the Lemurs) of a tendency to 

 the mode of the limb-plexuses to be " post-fixed " as compared 

 with the usual human type. [When comparable nerves in two 

 plexuses do not leave the cord at the same level, the plexus in 

 which this level is further from the brain is " post-fixed " as 

 contrasted with the other.] The tendency mentioned above will 

 be realized best by considering some actual results of dissections. 



Fig. 89. Communications between the upper thoracic nerves and the Sympathetic 

 cord in (A) Cynocephalus mormon, a representative of the Cercopithecidae, and (B) 

 a Lemur. In (A), the second thoracic nerve (Th'2) is seen to divide, and the upper 

 branch of division joins the Brachial plexus. (From dissections by W. L. H. D.) 



The brachial plexus in a series of primate animals has provided 

 information which may be tabulated as follows : 

 Plexus brachialis. 

 I. Nervus axillaris : Segmental derivation in terms of cervical 

 nerves. 



Man : C 5 (or C 4> C 5 ). (Harris 1 .) 



Cercopithecidae: C 6 , C 7 . (Kohlbrugge 2 .) 

 (and Lemurs). 

 1 J. A. P., July, 1904. 2 Xon. Ak. van )Vct. Amsterdam, 1897. 



