472 PHYSIOLOGICAL si: KM 



always) separated from the parallel (postsylvian) sulcus, but nuuu-r..u> 

 fragmentary sulci, and a backwardly-directed hook at the upper CM id 

 of the suprasylvian (Sylvian) sulcus, or a forwardly-directed hook to 

 the postsylvian (parallel) sulcus, serve to remind us of the old link 

 between these two sulci, which has been broken. 



The lower end of the suprasylvian sulcus in the Lemurs overlaps 

 the upper part of a pseudosylvian sulcus (of the feline type), the gyrus 

 between the two sulci becomes submerged, and the resulting sulcus 

 we now call the " Sylvian fissure." The lower end of the supra- 

 sylviau sulcus can be seen in many Prosimian hemispheres emerging 

 from the front of the " Sylvian complex " a short distance above the 

 rhinal fissure. 



In the Apes the submerged area increases in extent and is culled 

 the " insula." It is hidden by two opercula ; and a comparison of a 

 large series of Ape-brains seems to clearly demonstrate that the dorsal 

 limiting sulcus of the insula is no other than the suprasylvian 

 sulcus. 



In no brain does this sulcus extend so far (in the ventral direction) 

 as the rhinal fissure. In many of the larger Apes it emerges slightly 

 and cuts into the anterior lip of the Sylvian fissure. In 7///AA//V.N-. 

 Simia, and the Antliropopitlieci it extends forward upon the surface 

 so as almost to reach the fronto-orbital sulcus. 



The early history of the latter sulcus is not satisfactorily known. 

 It is present in an exceedingly well-developed condition in all the 

 Simiidac, and in a less obtrusive form in many of the larger Ape* 

 but, on the other hand, it is absent in many of the Cebido) and Cer- 

 copithecida). Such being the case, it is very surprising to sometimes 

 find in the Lemurs a small sulcus, which can be no other than the 

 fronto-orbital. It is impossible to say with any degree of probability 

 whether this sulcus is represented beyond the limits of the Primates. 

 The diagonal sulcus of the Carnivora, Ungulata, Edentata (JtrnttttjHts, 

 Myiinecophaya) occupies a position analogous to that of the fronto- 

 orbital in the Primates. 



In the Anthropoid Apes there is a pronounced tendency for the 

 anterior lip of this (fronto-orbital) sulcus to become opereular and 

 to extend backward over the insula, the anterior limit of which is 

 marked out by the sulcus itself. 



This process of operculation may be carried very far even in /////(/- 

 fxttes, Simia, and Anthrojiopilhecus ir<>!/!<I ii/< s \ ;md in one specimen of 

 Anihropopitliecus gorilla (D. 056) a very close though spurious imita- 

 tion of the human condition of this re-ion i.s attained. 



In the human brain thia process of open ulat inn :<n.r,ill\ 1 ,ids to 



