24- THE KUE SEALS OF THE PKIBILOF ISLANDS. 



the Sylvian extends in a dorso-caudal direction, Inclining somewhat toward the verti- 

 cal. Apparently it terminates in a fork, but when the walls of the fissure are divari- 

 cated it is seen that the cephalic or anterior branch is really another fissure, which, 

 after its, superficial union with the Sylvian, becomes a submerged fissure lying just 

 beneath the surface in its cephalic wall and running parallel with it to the base of the 

 brain, but not actually connecting either with the Sylvian or with the rhinal. The 

 Sylvian, on account of the subflssural complication, appears to be a larger fissure than 

 it re'ally is. 



In a former paper' attention was called to the fact that this vertical fissure (super- 

 ficial vertical branch of the Sylvian) had been mistaken for the true Sylvian. Both 

 fissures are well marked and can not be ignored ; but it is an unusual circumstance for 

 the Sylvian to assume a strictly vertical position in the adult, and there would, more- 

 over, remain a fissure in the usual situation of the Sylvian unaccounted for. In my 

 former paper I designated this vertical fissure as the anterior of the Felidw, and found 

 at a later date, while consulting Krueg's article,^ that he questioningly represents a 

 similar fissure by the same name in Fhoca vitulina. Gallorhinus, while showing this 

 fissure similarly situated, instead of elucidating the complications seems rather to.add 

 to them and to suggest a probable doubt as to the correctness of the homology with the 

 anterior fissure. Indeed, the conditions are strongly suggestive of its being nothing 

 more than the frontal portion of the supersylvian fissure. An examination of the 

 brains of certain bears tends to illuminate this view. In the family Ursidw, as in the 

 Ganidce, the supersylvian forms a complete arch, the caudal portion being known as 

 the posterior supersylvian (Krueg), or postsylviau (Owen). The frontal portion of 

 this arch varies in its distance from the Sylvian. Occasionally the frontal and caudal 

 portions are about equally distant, but when there is any difference in this distance 

 it appears that the frontal portion approaches more closely to the Sylvian than does 

 the caudal. In JJrsus Q,rctos, or the brown bear, Krueg figures the frontal portion 

 of the supersylvian as approximating very closely to the Sylvian. The condition in 

 GallorJdnus might be considered as a stage just beyond this. In the brown bear the 

 frontal portion of the supersylvian is still visible upon the lateral surface close to 

 the Sylvian. In the case of the seal it has passed over the brink, so to speak, and 

 is no longer visible its entire length on the lateral surface. The following diagrams 

 will illustrate the conditions more clearly : 



Bear. 



Seal. 



A diagrammatic representation of the relation of the Sylvian and supersylvian fissures in the bear and seal, as if seen in 

 section. Prss., presupersylvian ; Syl., Sylvian fissure. 



At the bottom of the Sylvian fissure lies the insula, presenting but a slight degree 

 of development. There is a suggestion of a circuminsular fissure, but in other respects 



' 1896, P. A. Fish : A note on the Cerebral Fisauration of the Seal (Phoca vitulina). Jour. Comp. 

 JSTeurol., VI, 15-19. 



= 1880, J. Krueg: Ueber die Furohen auf der Grosshiroriude der zonoplacentalen Siiugethiere, 

 Zeit. f. wiss. Zoologie, XXXIII, 595-672, 5 plates. 



