262 THE LOWER PRIMATES 



have connections with the lower portions of the neuraxis. They provide a 

 series of reflex ares which participate in the balancmg function. That this 

 function is primarily the concern of the lower segments of the brain below the 

 cliencephalon and endbrain seems clear on the basis of ontogenesis. It may be 

 held with a fair degree of certainty that the reflex arcs made possible through 

 the vestibular nuclei of the oblongata, perhaps supplemented by influences 

 from the midbrain, are sufiicient for a considerable period of tmie m early 

 life to carry on the reflex activities involved in the balancing reaction. 



CONNECTIONS OF THE VESTIBULAR NUCLEI 



The several connections of the vestibular nuclei become ol considerable 

 importance in this relation. These nuclei, as already indicated, are primarily 

 connected by afferent fibers with the proprioceptors of the internal ear, 

 including the saccule, the utricle and the semicircular canals. The nuclei have 

 connection with the vermis of the cerebellum through the corpus juxtaresti- 

 forme, also with the midbrain, particularly the oculomotor nuclei. 



COMPARATIVE DIMENSIONS OF DEITERs' AND SCHWALBe's AREA 

 IN THE LOWER PRIMATES 



Conclusions based on comparative dimensions of Deiters' and 

 Schwalbe's nuclei respectively indicate that the function of balancing and 

 maintaining the optimum physiological posture in all of the primates is 

 essentially the same in efleetiveness. Deiters' nucleus throughout the primate 

 series manifests strikingly constant dimensions. It presents a maximum 

 variation in its planimetric coefficients of less than 7 per cent, while its 

 variation in its longitudinal coefficients does not exceed 4 per cent. In the 

 case of Schwalbe's nucleus apparently the same constancy obtains in so far 

 as the planimetric coefficient is concerned, although in the comparative 

 longitudinal measurements of the nucleus a variational range of 6 per cent 



