NERVOUS SYSTEM. VERTEBRATA. 475 



little importance. Not unfrequently this sulcus joins a small anterior 

 rhinal fissure thus completing the resemblance to the junction of the 

 " presylvian " sulcus with the rhinal in the Carnivora and others. 



The coronal sulcus of the non-Primate mammals may be represented 

 in the inferior frontal and the inferior precentral sulci of Mun. < MI. 

 of the earliest sulci to make its appearance in the developing Carnivore 

 and Ungulate brain is the coronal. In the Carnivores it often joins 

 the lateral sulcus, in many Ungulates it is linked to the suprasylvian, 

 in the Pig-family it is united with the intercalary sulcus. In ihe 

 Primates the so-called sulcus rectus exhibits a similar precocity, and 

 occupies a position not unlike that of the coronal in the Ungulates 

 and the primitive Viverrine Carnivores. It becomes split up in the 

 Cebidaa and Cercopithecidae into two parts, the sulcus rectus (gttutn 

 stricto) and the sulcus arcuatus. The former develops into the 

 inferior frontal and the latter into the inferior precentral sulcus. 



The problem of the exact interpretation of the central (Rolando's) 

 sulcus presents many difficulties. There can be no doubt whatever as 

 to the homology of the mammalian lateral with the intraparietal sulciw 

 of the Primates, and the interpretation of the ansate as the ramus 

 postcentralis superior is almost as sure. We find in the Carnivora and 

 the Primates respectively a deep and important sulcus bearing the 

 same relations to the ansate and lateral sulci. In the former we call it 

 <* crucial " and in the latter " central " ; the solution thus naturally 

 suggested is that the central sulcus of the Primates represents the 

 crucial sulcus of the Carnivora. Such a view has often been pro- 

 pounded before, and has in several instances been discarded for no 

 valid reason. Thus it has been urged (with a singular disregard for 

 the facts of the case) that the crucial sulcus "belongs to the mesial 

 wall," in spite of the patent evidence afforded by the Arctoid Carnivora 

 that when the crucial sulcus becomes dissociated from the intercalary 

 sulcus it often lies wliolly on the dorsal surface of the hemisphere 

 (see the brain of the Bears, the Glutton, and in fact most 'of the 

 Arctoidea). 



If we study the forms assumed by the crucial sulcus in the large 

 Carnivores (such as the Bears and Seals) and by the central sulcus 

 in the large Apes (Simiidaj), we cannot fail to be struck witl 

 striking parallelism, which could only be produced by the operation 

 of similar factors in the two cases. Moreover, the earliest phases 

 the development of the central sulcus in the Lemurs are similar to tk 

 first rudiments of the crucial sulcus in the Viverrida). 



Physiological evidence (which, however, in such matters is notori- 

 misleading) does riot altogether support such an homology. In the 



