374 THE INTERMEDIATE PRIMATES 



nuclear masses there is complete correspondence in all species thus far 

 considered, from which it must be apparent that a definite principle of 

 structural design regulates the manner in which this series of nuclei is laid 

 down in the brain stem. 



Beginning at the caudal extremity of the oblongata are the nuclei for 

 discriminative sensibility in the tail, leg and arm; immediately succeeding 

 them in the next higher lc\els are the nuclear relay stations receiving 

 impulses from the proprioceptors of the internal ear in the interest of the 

 balancing function. Thus a superposed series of nuclei in the dorsal lield of 

 the oblongata in the form of a long column makes provision for the primary 

 relay of all sensory impulses arising in the proprioceptors of the body. This 

 is not merely of generic significance, for its long antecedent history in the 

 vertebrates makes it a matter of phyletic moment. 



Lateral to Deiters' nucleus, forming the extreme lateral structure of the 

 cross section, is an elevation on the surface of the axis, the tubcrculum 

 acusticum (Tub), into which enter some of the fibers of the cochlear divi- 

 sion oi the eighth nerve (N8). This elevation forms a relay station in the 

 pathway of hearing, so that in the tuberculum acusticum and the two vestibu- 

 lar nuclei at this level, the chiet receiving stations for the eighth nerve appear. 

 Interposed between the tuberculum acusticum and Deiters' nucleus is a 

 dense oval bundle of fibers constituting the restiform body ( ICP). 



A4ention should be made of the large size of the vestibular area, inas- 

 much as this element of the brain stem causes a pronounced elevation in 

 the lloor of the fourth ventricle. Furthermore, the large dimensions of the 

 vestibular complex in macacus indicate to what extent the balancing func- 

 tion is necessary in this animal. 



Another feature at this level is the inferior olivary nucleus (10) con- 

 nected with which are the two accessory olivary nuclei. Attention is 

 especially called to the clear-cut boundaries of the inferior olivary nucleus 



