NERVOUS SYSTEM. VERTEBRATA. 419 



D. 624. The brain of a Malbrouck Guenon (CercopitJiecus cyno- 

 surus) : the left hemisphere has been detached. 



Both brains conform precisely to the typical arrange- 

 ment. O.C. 1338 E^. 



D. 625. The brain of a Yellow Baboon (Papio babuin),(<s): 

 the left hemisphere has been separated. 



This is a very much larger brain than that of any of the 

 Primates yet considered. The cerebral hemispheres are 

 also proportionately longer than in the other genera. 



In accordance with its greater extent, the surface of the 

 hemispheres is more richly furrowed than in the smaller 

 Cercopithecidse, but its pattern is essentially the same. 



The Sylvian fissure is separated from the parallel sulcns 

 throughout by a wide exposed gyrus. The parallel sulcus 

 is prolonged far beyond the Sylvian, and its apex is 

 encircled by the ramus horizontalis of the intraparietal 

 sulcus. The latter splits and forms a transverse occipital 

 sulcus, but, unlike the condition found in the Apes hitherto 

 considered, the mesial limb of the transverse occipital cuts 

 deeply into the mesial wall of the hemisphere, so that it 

 represents (functionally) the sulcus of Macacus (vide 

 supra}. Such being the case, it is not surprising to find 

 that the parieto-occipital sulcus (which in a superficial view 

 of the left hemisphere seems to join the intraparietal 

 element) cuts into the anterior wall (and not the posterior, 

 as in the higher Oebidse and in the Macaques) of the 

 intraparietal ramus. On the right side the parieto-occipital 

 sulcus lies wholly in front of the ramus intraparietalis. On 

 both sides the former sulcus appears to join the calcarine, 

 but a submerged gyrus separates them *. 



There is a well-developed occipital operculum, which has 

 been partially removed on the right side in order to expose 

 the transverse occipital sulcus. No proper operculum is 

 formed by the upper lip of the horizontal inferior occipital 

 sulcus. 



Three horizontal sulci, representing the transverse 



* By parieto-occipital sulcus is meant that labelled y in Macacus, which, 

 as explained above, does not strictly represent the parieto-occipital sulcus o 



Human Anatomy. 



2fi 2 



