PAPIO C^'NOCEPHALUS 317 



lesions in and experimental disturbances of the two nuclear structures pro- 

 duce definite disturbances in equilibration. These two nuclei, therefore, have 

 been accepted as the principal relay stations for transmission of impulses 

 necessary to the iiiaintenance of the proper balance oi the body. They thus 

 become of primary importance in relation to the balancing mechanism. 

 Their size and general relations with reference to the rest of the section fur- 

 nish some conception of the degree of balancing function necessary to the 

 animal in order to maintain its equilibratory adjustments. 



The dimensions of the vestibular nuclei in the baboon indicate that its 

 balancing requirements have not increased materially o\er those of the 

 lower primates; in fact, the numerical estimation of the area occupied by 

 these structures would show the vestibular nuclei to be somewhat smaller 

 than in any of the species already considered. This may be due to the fact 

 that the baboon carries on its life for the most part upon the ground, and with 

 the exception of a few species is not a tree-living animal. It has not acquired 

 the erect posture, and hence has placed no further obligations upon the 

 balancing mechanism due to maintaining equilibrium on two feet. 



In the extreme lateral region of the medulla oblongata is a portion of 

 the enlargement forming the tuberculum acusticum (Tub) into which enter 

 libers from the cochlear division of the eighth nerve. Immediately mesial to 

 these fibers are some vestibular fibers w'hich take origin in the propriocep- 

 tors of the vestibule of the internal ear. These fibers pass inward and back- 

 ward; some of them lateral to the descending tract of the fifth nerve, some of 

 them actually penetrating this bundle to reach the nucleus of Deiters 

 (ND). Situated between the tuberculum acusticum (Tub) and Deiters' 

 nucleus (ND) is the large oval bundle of densely compacted neurons 

 comprising the restiform body (ICP). In this bundle are assembled 

 the ascending libers from the spinal cord and oblongata on their way 

 to the cerebellum. The libers arise from several dilferent sources and 



