6o Journal of Comparative Neurology, 



joins the tentorium there is an extension of this osseous tissue 

 in a vertical direction into the falx, a circumstance which cer- 

 tainly is not common in the majority of other animals but has 

 been noted by Turner in Macrorhhms. 



Terminology . With the existing uncertainties relating to the 

 homology of the fissures of the brains of the carnivora and that 

 of the human species, much confusion has resulted in the pre- 

 sent nomenclature. Some have made a direct homology, 

 others have proposed a fissural type solely and only for the 

 lower forms, while still others have blended the two and some 

 have utilized a system of names devised by themselves. On the 

 lateral surface of the various fissured brain types there is at least 

 one fissure — the Sylvian — which is quite constantly present, and 

 on the mesal surface, the hippocampal fissure. 



In the matter of nomenclature no attempt has been made 

 to follow the law of priority, but those fissural names, whether 

 of old or recent date which seemed most appropriate concern- 

 ing position and relation, have been adopted, and, with perhaps 

 but one or two exceptions, no new names have been introduced. 

 It has been the purpose to use an intrinsic terminology and to 

 substitute for the sometimes indefinite terms, anterior, poster- 

 ior, superior and inferior, terms of more universal applicability, 

 cephalic, caudal, dorsal and ventral. For cephalic and caudal 

 Professor Wilder has recently suggested praeal and postal as 

 equivalents, and for cephalad and caudad, praead and postad. 



Where certain of the fissures or gyres have been submerged 

 for a portion or the whole of their course, they have been des- 

 ignated as such, or the equivalent terms, subfissure or subgyre 

 proposed by Wilder, have been used. 



In the study of fissures mere surface appearances are not 

 accepted as final. A fissural entity is not always easy to define. 

 The best apparent guide is the relative depth throughout the 

 course of the fissure. We may commonly assume that the 

 greatest depth is at about the middle of its length and that it 

 becomes gradually shallow toward each end until it reaches the 

 surface. Such a simple condition, however, does not usually 

 exist. One fissure may join the end of another, giving the ap- 



