MOT^PllOLOGY or Till' BRA IX IX THE MA^nfAlJA. 405 



happens in the Mammalia as a \vh()l('. Next in order follows tlie post sylvian snlcns, 

 again as in other mammals. And iinally, Ili(> most variable I'ro^iniian tx'atnres — the 

 postlateral, diagonal, and cnicial lurrows— ar(> exactly tliose wliiuh coine next ia the 

 order of frequency imiong mammals in general. 



The homologies thus suggested are so revolutionary and so opposed to all the current 

 teaching, that it is necessary to submit each sulcus seriatim to the closest scrutiny in the 

 light of all the comparative evidence available, either in the facts of direct observation 

 or in the writings of other anatomists. At the same time, it will be cjiivenient to extend 

 the range of comparative studies and Include the Apes and Man. 



The Morphology of the Sylvian Fissure. 



The Sylvian fissure is found in its complete and typical form only in tlie human brain. 

 The p)erij)heral lips of three sulci become opercular and appi-oach until they meet : the 

 peculiar pattern thus formed upon the surface by the meeting of these labia is commonly 

 called the Sylvian fissure. 



The region which becomes overlapped by the oporcula is called the insula E/Cilii and 

 is bounded by three sulci — the inferior, superior, and anterior limiting sulci. If the 

 human brain be compared with a sufficiently complete series of brains of Primates, it 

 will become so obvious as to amount to an absolute demonstration that tlie inferior 

 (morjjhologically posterior) limiting sulcus represents the pseudosylvian, the superior 

 limiting sulcus the suprasylvian, and the anterior limiting sulcus the diagonal sulcus, 

 respectively, of the Lemurs and other mammals. 



It has been clearly shown by Marchaud * and Cunningham f that the anterior limiting 

 sulcus of the island of Reil is the liomologue of the fronto-orbital sulcus of the 

 ^Vnthropoid Apes. If anyone is disposed to dispute this contention and follow the lead 

 of Herve, Eberstaller, Waldeyer, and Giacomini (among others), a glance at the series of 

 brains of Anthropoid Apes, and especially those of the Gorilla, in the Museum of the 

 Royal College of Surgeons will convince him of liis error J. The anterior limiting sulcus 

 of the insula is cei'tainly the homologue of the fronto-orbital sulcus of the Apes. The 

 latter is best developed in the genera Aiithropopithemts, Simia, and Ili/lobates, but is 

 constantly found in a less well-developed condition in Scmuopilhecus, Papio, and 

 frequently in other genera of Old-World Apes and sometimes also in the larger members 

 of the family Cebidtc. 



In the Hapalid:e and the smaller Cebidoe, and sometimes also in tlie smaller Cerco- 

 pithecidae, this sulcus is absent. It is therefore interesting to note its presence in many 

 individuals of the genus Lemur as well as in some of the Indrisintc. Undue importance 

 nmst not, however, be attached to tiiis fact, because the fronto-orbital sulcus of the 

 Lemurs and Ajies is almost certainly the homologue of the diagonal sulcus of the 

 Carnivora, Ungulata, and Edentata. 



* "Die Morphologic des Stirnlappens uiid der Insel dor Aiitliropomorplien,"' Jena, 1^:);3, pp. 91 et sc'i (Arbeiteii 

 aus d. patholog. Inst, zu Marburg, Bd. ii.). 



t " The Insular District in the Cerebrum of the Anthropoid Ape.s," Journ. of Anat, and Phys. vol. xxxi. pp. 1 cl sc'i. 

 t See especial!}- specimen D. G58, Coll. Surg. Catalogue, p. -io'J. 



