HYLOBATES HOOLOCK, THE GIBBON 427 



the author. The repetition would be wholly objectionable and out of place 

 were it not for one compelling argument which seems to make it justifiable. 

 To recognize the morphological consistency, the unity of structural design, 

 in the relation of so many intricate parts should suffice to dispel all doubts 

 concerning the close generic association of these animals. This unity is like- 

 wise convincing as to that iniluence which, working through the primate 

 stock, has employed the same fundamental pattern to establish such condi- 

 tions as result in progressively more efficient neural mechanisms and in 

 better behavioral adjustments. 



LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLIVE (FIGS. 201, 202) 



Here the most conspicuous feature is the appearance of the inferior 

 olivary nucleus (10). This structure here presents its full degree of devel- 

 opment in the gibbon. Certain features of it are to be contrasted with 

 the homologous structure in the lower primates. It has gained considerably 

 in its general dimensions, both transversely and longitudinally. But its real 

 increase in prominence is due to its more convoluted configuration character- 

 istic of the human and humanoid structure. In connection wTth it are its two 

 accessory olives (VO, DO). The central gray matter occupies a position 

 immediately beneath the floor of the fourth ventricle. In its most mesial 

 portion it contains the nucleus of the twelfth nerve (Nhy), whose emergent 

 fibers (N12) pass from the nucleus and make their way ventrolaterally 

 toward the inferior olive. Lateral to the nucleus hypoglossus, and separated 

 from it by the sulcus limitans in the central gray matter, is the dorsal 

 nucleus of the pneumogastric nerve (Nvd), some entering fibers of which 

 may be discerned approaching this nuclear collection. Immediately adjacent 

 and lateral to the dorsal nucleus of the tenth nerve is a dense collection of 

 medullated fibers constituting the fasciculus solitarius surrounded by the 

 nucleus of this fasciculus (Nfs). Ventral to the fasciculus solitarius is the 



