NERVOUS SYSTEM. VERTEBRATA. 401 



part of its extent, and from its apex a deep cleft extends 

 on to the mesial surface of the hemisphere. The depth of 

 this cleft (which we may call the ramus parieto-occipitalis 

 sulci intraparietalis) is expressed by its length on the 

 mesial surface (fig. 238, x) . 



The parieto-occipital sulcus is swept, as it were, into 

 the mesial part of this great cleft *. It emerges near the 

 ventral extremity of the latter, and fuses with one of the 

 two "compensatory" sulci. Thus a V-shaped sulcus is 

 produced which is parallel to the calcarine sulcus and the 

 upper part of the retrocalcarine. 



At a superficial glance the Simian sulcus seems to join 

 the posterior limb of the V-shaped intraparietal sulcus. 

 But on separating the lips of the sulci it will be seen that 

 the shallow Affenspalte lies entirely behind the deep intra- 

 parietal. In fact the r6le (which is assumed by the 

 Affenspalte in many CercopithecidaB) of relieving the 

 tension of the expanding occipital regions is fulfilled by 

 the operculation of the posterior lip of the ramus parieto- 

 occipitalis sulci intraparietalis, rather than by that of the 

 Simian sulcus. 



The Affenspalte becomes much deeper, and its posterior 

 lip slightly opercular in its lateral part. On the left 

 hemisphere it (superficially) joins the inferior occipital 

 sulcus, the upper lip of which is also operculated. On the 

 right hemisphere the Simian sulcus is much more poorly 

 developed, but its posterior lip is operculated in its whole 

 extent. It is separated from the inferior occipital sulcus 

 by a wide interval, and not merely by a narrow submerged 

 gyrus, as on the left side. 



There is a T-shaped calcarine complex. The long col- 

 lateral sulcus is superficially joined to the retrocalcarine 

 sulcus (fig. 238, SULC. P. CALC.). 



The superior limiting sulcus of the insula (the supra- 

 sylvian sulcus of other mammals) emerges anteriorly from 



* The parieto-occipital sulcus of Human Anatomy really consists of two 

 separate sulci (corresponding to those just referred to as ramus parieto- 

 occipitalis of the intraparietal and the parieto-occipital sulcus) submerged 

 in the one cleft as in this case, but the dorsal sulcus does not join the intra- 

 Darietal as it does in this brain. 



VOL. II. ^ D 





