MORPHOLOGY OF THE BHA]\ IX Till- .MAMMALIA. H :l 



lateral, ansate, and coronal sulci*; the sulcus wliidi I distinqaiislied as "coronal" he 

 regards as the prorean ; and lie agrees with me in the rccogaitiou of liu^ sulcus/ as part 

 of the central sulcus. The latter sidcus is considered by Flatau and Jacobsohuf to 

 represent the superior precentral sulcus, because it occupies a positiou iu relitiou to the 

 intraparietal sulcus analogous to that whii-h is presented iu the ])raiii of Apes. 



I shall discuss first of all the representatiou of these sulci in (he general body of 

 mammals, and then follow the evolution of (he corresjTOnding furrows in the Apes. 



If we follow the example of Ziehen, aud limit our mammalian horizon to such 

 specialized Carnivores as Caii'is and Fhoca, neglecting all the generalized Carnivores and 

 the Ungulates, Edentates, and llodenls, we might perhaps arrive at the same conclusion 

 and regard the sulcus I have called " lateral" as the homologue of the conjoint corono- 

 lateral furrow of many Carnivores. If, however, w^e study the developmental tendencies 

 not only in one or two specialized forms, but in the whole Mammalia (in such a manuer 

 as I have roughly sketched out already), the whole evidence will point to the conclusion 

 that the sulci which I have called "lateral" and "coronal" respectively are in reality 

 the homologues of the sulci of the same names in rirerm, l^rocaria, and all mamniais. 

 In other words, the coronal sulcus, inst(-ul of being represented in the furrow which I 

 have called "lateral," as Ziehen would have us believe, really exists in the Lamurs as 

 the separate sulcus which I have called " coronal." The latter sulcus (Ziehen's r) is 

 regarded by the same writer as tlic houiologue of the prorean. 



The prorean sulcus has a peculiar distril)ution in the mimnnlian series. It is seen in 

 both the Polyprotodont(r/////«e///».<.) and Diprotodout Marsupials (Macropodidae, P/i«s(?o- 

 lomys, and extinct Thylacoleo), in 3[iii-niecoph(i<i(i and Orncfcropiis alone of the Edentata, 

 and reaches the height of its development iu the Carnivora, and especially iu some of the 

 Arctoidea, such as Gulo. If we seek for this sulcus iu the more "■eueralized Carnivora 

 and especially tlie Viverrida:-, no such separate element as the prorean sulcus will be 

 found. In the Viverrida^ the coronal sulcus is prolonged forward so as to take the 

 place, functionally, if not morjihologically, of the prorean sulcus. 



A similar phenomenon occurs in nrost Ungulates, ami in the generalized Hyrax 

 (Procaria) the coronal sulcus extends far forward on to the apex of the hemisjjhere. 

 Much light is thrown upon this perplexing problem by a comparison of the arrangemi^nt 

 of these sidci in certain llodents aud Edentates with that found in other mammals. 



In the Carnivora the coronal is sejjai'ated from the ^^rorean sulcus by a mesial extension 

 of the orbital (presylvianj sidcus. This ])rolongation is certaivdy a purely mechanical 

 phenomenon; i.e., the tension of the growing cortex becomes relieved by the extension 

 of a pre-existing furrow, which in this case is the orbital. In Ori/cteroptis, and some- 

 times in 3Iyrmecophngfi, the mesial prolongation of the orbital is united not only with 

 the prorean but also with the anterior end of the coronal sulcus. In the l)rain of 

 Dolichotis (Rodentia) the orbital sulcus is not prolonged beyond its morphological limits 

 (if such a phrase is permissible), but the corono-proreau complex retains a form which 

 is curiously reminiscent of the united coronary and prorean sulci in Oi-yctei'opiis. This 



* Arcli. f. I'sycliiat. Bd. xxviii. p. iil'l. t llaiiJbucli, p. ITS. 



