498 THE HIGHER ANTHROPOIDS 



from the Miniis to the lateral lobes, w hile two paraniediaii sulei interiLipt the 

 eoiirse of the folial sulci on the occipital surface. In their hiteral expansion, 

 the occipital surfaces of the lateral lobes are neither so broad nor so long as in 

 the case of the still higher j^riinates. There is, however, a decided advance in 

 all of these respects as compared with tlu' lower and intermediate [jrnnates. 

 The petroso-ventrieular surface of the cerebellum shows no departure from 

 the conditions obser\ed in the lower forms. A relatixely small lloeeulus 

 occupies the cereliello-pontile angle mto relation \\ith which also enters a 

 large middle cerebellar peduncle. 



THE BRAIN STEM 



The Medulla Oblongata. The brain stem in its oblongatal portion 

 shows distinctive leatures along its ventral surlace. The ventromedial! sul- 

 cus is in relation upon either sidi' with twci elevations lormmg the pyramids 

 which taper at their caudal extremities to a le\ el where interlacing bundles 

 ol the decussation cross the sulcus. A well-delmed pre()li\ary sulcus separates 

 the pyramid Irom a prominent olivary eminence, which latter is in turn 

 separated from the sj^inocerebellar eminence by tlu' postolivary sulcus. 

 An intermediate sulcus indicates the boundary between this latter eminence 

 and the eminentia trigemim. Upon the dorsal surlace both the cuneus and 

 the elava are prominent and separated Irom each otlu'r by the dorsal para- 

 median sulcus. As to relatixc Nolume, the ratio ol the cla\a to the euneus is 

 about one to two, thus indicating Irom surlace markings at least a prej:)onder- 

 anee ol incoming sensory impulses Irom the upper e\tremit\ antl hand. 

 This accords with the failuri' on the part of tin- animal to develop a tail and 

 also w ith the progress which it has made in its maiuial diilerentiation. 



The dorsal aspect ol the oblongata comprises its two characteristic 

 surfaces, the jnlraventricular and the \ (.ntncular. The \entrieular surlace 



