398 TEOF. G. ELLIOT S^riTII ON THE 



sulcus on tlie mesial surface (with wliicli at present we are not concerned) and tlie 

 Sylvian fissure on the outer surface. It might reasonahly be assumed therefore that, 

 if the sulcus usually called " Sylvian fissure" in the Carnivora were correctly so-called, it 

 would be the most constant and most precocious furrow^ on tlie outer aspect of the 

 neopallium. But this is not so. For if the developmental history of the neopallial sulci 

 be studied in any Carnivore *, it will be found that several sulci, such as the suprasylvian 

 and corona], make their appearance long before the pseudosylvian sulcus. Then, again, 

 if the brain be studied in the whole assemblage of Carnivores, it will be found that the 

 suprasylvian, coronal, and lateral sulci exhibit far greater stability and maintain their 

 characteristic features with far greater constancy than does the pseudosylvian sulcus. 

 And in the more generalized and primitive Viverridai the latter becomes very imperfect 

 and inconstant, and even at times disappears entirely. Occasionally the same 

 phenomenon occurs in some of the other Carnivores: I have seen the pseudosylvian 

 sulcus of the Cat reduced to very diminutive proportions, and the ectosylvian sulci 

 deepened to compensate. It is clear, therefore, that the so-called "Sylvian fissure" of 

 the Carnivora is not the morphologically stable and precocious furrow which we should 

 expect if it were the true representative of the similarly-named feature of the brain in 

 the Primates. Moreover, the nature of this false Sylvian furrow varies considerably 

 within the limits of the Carnivora. In the iEluroidea, as for example in the Cat's brain, 

 the lips of the pseudosylvian sulcus are formed by the first arcuate gyrus of Leuret, i. e. 

 the strij) of neopallium Avhicli is bounded peripherally by the ectosylvian sulci. In the 

 Arctoidea (as was long ago demonstrated by Sir William Turner, and recently confirmed 

 by Holl and the writer [Catalogue of Royal College of Surgeons t]), the w'hole of the first 

 arcuate gyrus is buried in the false Sylvian furrow, so that the lips of the latter are 

 formed not by the first (as in the Jilluroidea) but by the second arcuate gyrus of Leuret, 

 -/. e. by the area bounded peripherally by the suprasylvian and postsylvian furrows. 

 And in the Pinnipedia (as I have recently shown in the above-quoted Catalogue, p. 2S6) 

 the whole of the anterior limb of the second arcuate gyrus tends to become buried in the 

 great cleft-like so-called " Sylvian fissure," so that in many Seals the anterior lip of the 

 furrow is formed by the third arcuate gyrus of Leuret. And if a series of Carnivores be 

 examined, all intermediate stages will be found between these extreme types. 



Moreover, it has been show'n by Holl %, who has so admirably demonstrated the real 

 nature of the so-called "Sylvian fissure" in Carnivores and Ungulates, that the 

 claustrum also extends beyond the area depressed in the pseudosylvian sulcus, even in 

 the Arctoidea ; so that, if anyone is inclined to attach importance to this structure as an 

 indication of the extent of the insula (or area submerged in the Sylvian fissure), it is 

 ol)vious that the pseudosylvian sulcus of Carnivores is in no sense homologous with the 

 true Sylvian fissure of the Primates. 



By far the most precocious and most stable sulcus on the lateral aspect of the 

 neopallium in the Carnivora is the suprasylvian (/. e., the furrow which most writers 



* I have examined embryonic brains of the Cat, Dog, and Bear, and have confirmed the teaching of Krueg 

 (Zeitsch. f. wissenseh. ZooL Bd. xxxiii.) iu this matter. 



t VoL ii. (2nd ed. VM'2) p. 277, fig. 154, % Arch. f. Anat. u. Bhys., Auat. Abth. 1899 and 1900. 



