464 THE INTERMEDIATE PRIMATES 



considered as definitely influenced by the possession of a prehensile tail. The 

 substantiation of this view in regard to the nucleus of GoII presents far fewer 

 difficulties than is the case with the nucleus of Burdach, yet the wider 

 range of motor performance made possil^le by the prehensile tail may be 

 urged as the basis of greater manual freedom and hence an increase in the 

 volume of afferent influx from the upper extremity. 



IV. The Vestibular Nuclei and Their Relation to 

 THE Balancing Mechanism 



The functional capacity of the balancing mechanism in the intermediate 

 primates, particularly as indicated by the nucleus of Deiters, appears most 

 prominent in the giblaon. This observation is borne out by the facts recorded 

 in connection with the surface markings of the oblongata in which the large 

 protuberances on the floor of the fourth ventricle occasioned by the vestib- 

 ular area were noted (p. 420). This preeminence of the gibbon in the index of 

 its balancing mechanism is undoubtedl}^ due to the adjustments necessary 

 in its arboreal locomotion. The differences in these three species with refer- 

 ence to the triangular nucleus of Schwalbe are not great. It is probable that 

 all three of these animals have nearly the same balancing problems to meet 

 in then" locomotion and station, which thus places their balancing mecha- 

 nism about on a par. The coeflicients of the vestibular areas in the macacus, 

 baboon and gibbon are given in the appended tabulation: 



Coefficients of Deiters' Area in the Intermediate Primates 



