510 THE HIGHER ANTHROPOIDS 



pyramid is the preolivary sulcus and, somewhat further along the pcripherj^ 

 of the section, a faint indenture marks the postoHvary sulcus. 



The impression created by this level of the brain stem makes more 

 clear the accessions in the dorsal sensory field which particularly affect the 

 column of Burdach. This appears to be related to tlie differentiation of the 

 forearm and hand. The substantia gelatinosa is relatively small, indicating a 

 less voluminous sensory contribution from the head and face than is the case 

 in many of the low er jjrimatcs. 



LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLIVE (fIG. 232) 



Here the large mass of gray matter occupying the ventrolateral portion 

 of the field constitutes the most prominent feature. This is the inferior olivary 

 nucleus (10) which in the orang-outang calls for special comment. In the 

 fu'St place, the size of the structure in proportion to the rest of the cross 

 section has obviously increased, thus indicating that the olivary functions 

 have proportionately acKaneed in their importance to the animal. In addi- 

 tion, there is distinct progress in the degree of eomolution or festooning 

 presented by the saccular wall of the nucleus, a feature which is more 

 particularly in exidence along the dorsolateral and ventromesial portion 

 than in the olivary fundus. A tliiicl feature is the somewhat clearer definition 

 of the nucleus as a whole, m contrast with adjacent structures. In this 

 respect, however, the degree of delinition marking tlu' bouiularii'S of the 

 inferior oli\e in the orang is less decisive than m chimpanzee, in gorilla or 

 in man. 



In view of tlu' function aseribed to the inferior oli\ar\ nucleus in this 

 discussion, it would appear that the orang is endowed \\ith a greater degree 

 of coordination between head, hand and e\ e and of eooixlinat ion of all skilled 

 learned performances than is the case in the lower primates. This is also 

 true to some extent m the comparison with the intermediate primates. 



