292 Susanna Phelps Gage 



acipenser and amia. In figure 93 is a representation of the 

 position and length of these folds as seen from the meson. 

 It is proposed to call these depressions, sidci, in analogy with 

 the term sulcus of Monro which is considered as a feature 

 of great morphological significance, and to differentiate these 

 endymal depressions from the fissiires of the ectal surface. 

 To a ridge between two sulci the term lophius, Gr. \6^o<i, 

 ridge, is proposed. " Rautenlippe " is ill adapted to English 

 and French, while furrow and ridge are not capable of univer- 

 sal application. 



In man. His has recognized that one sulcus, the sulcus of 

 Monro, has a morphological significance, indicating the bound- 

 ary in the cephalic region between the dorsal and ventral 

 zones (34). In the present investigation it has become evi- 

 dent that not only this and those of the metencephal but also 

 other sulci in the cephalic parts of the brain may be looked 

 upon as occurring at definite places with definite relations in 

 the three forms studied. In the region of the metencephal the 

 sulci are most clearly defined. In the larval diemyctylus the 

 mesen-and diencephal show sulci clearly. In the adult some of 

 these have become nearly obliterated on the endymal surface 

 but can be clearly seen in section by the bulging of the cine- 

 rea (p. 275). In lamprey the endymal surface is not much 

 thrown into folds and the cinerea is not clearly defined as in 

 the diemyctylus, but from definite points the cinerea is seen 

 to be continuous with the endyma, the cells, so to speak, 

 streaming off in definite channels. In the amia the sulci ap- 

 pear, but the indefinite arrangement of the cells does not as 

 yet help in the solution of the question. 



It is hoped soon to make a comparative study of these sulci 

 in different forms and to bring them into correlation, but cer- 

 tain of them are now definite enough to be used in the follow- 

 ing discussion. 



MESENCEPHAIy. 



The lobes of the mesencephal in the urodeles unite by a 

 broad band and form a slight depression, at least in diemycty- 

 lus, upon the dorsimeson (Fig. 24). In fishes, reptiles, etc., 



