BRAIN OF HAIR SEAL. 27 



splenium on the ventral aspect, and it apparently terminates in a wide fork or else 

 enters a fissure passing at right angles to its own course. Sounding the fissure at 

 this point gives some indication of a shallow separating the dorsal branch of the 

 fork. Following the appearances designated by Krueg in his diagrams of the condi- 

 tions found in some of the carnivora, the splenial proper includes the ventral branch 

 of the fork, while the dorsal branch may represent what he calls the postsplenial. 

 On the left hemicerebrum the splenial fissure penetrates the hemicerebral margin and 

 appears for a short distance on the dorsal surface. A smaller but well-defined fissure 

 lies in front of the splenial. On the left side it cuts the dorsal margin. For the 

 present we may designate it as the presplenial fissure. It corresponds very well with 

 the fissure which Kiikenthal lias called fissura sublimica anterior. 



The marginal or sapersplenial just passes the meso- ventral margin of the hemi- 

 cerebrum about 10 millimeters caudad of the splenial. It extends approximately 

 parallel with it to the dorsal mslrgin, which it cuts, and on the right hemicerebrum 

 extends on the dorsal surface for about 15 millimeters. On the left hemicerebrum 

 the fissure branches just at the margin. The main portion, however, continues 

 laterocephalad for about 20 millimeters. In the gyre between the splenial and 

 marginal fissures a well-represented secondary fissure is seen. 



A well-defined but unnamed fissure lies on the meso- ventral surface. It arises at 

 the caudal margin atid proceeds in an angular course toward the ventral end of the 

 splenial; it then swerves laterocephalad and terminates not far from the postrhiiial. 

 Its position corresponds approximately to the collateral fissure in the human brain. 

 This tentorial surface of the cerebrum has numerous secondary fissures and 

 branchings, some of which seem large enough to merit special mention. One such 

 inconstant fissure, lying parallel with the postsplenial, suggests a similarity to the 

 occipital. It cuts the hemicerebral margin slightly, and the relation of the lateral 

 fissure at this point suggests in a way the paroccipital of man. This occurs on the 

 left hemicerebrum. On the right the postsplenial has much the same appearance. 



At the cephalic end of the mesal surface beyond the genu of the callosum there 

 are two pretty well marked fissures. The one nearest the callosum corresponds to 

 the genualis of Krueg; part of falcial, Owen; or falcial. Wilder. On each 

 hemicerebrum this fissure cuts the dorsal margin slightly. Tlie other and more 

 slightly developed fissure lies nearer to the olfactory bulb. It does not reach the 

 dorsal margin, but extends farther in the ventral direction. This fissure corresponds 

 to the rostralis of Krueg; part of falcial, Owen; or subfalcial, Wilder, 



PHOCA VITULINA. 



The frontal portion of the cerebrum is more foreshortened than in Gallorhinus, 

 and there is therefore a slightly different arrangement of corresponding fissures 

 in that region. One of the most striking differences is the olfactory portion of the 

 brain. In Gallorhinus it is the larger, the olfactory bulb is of considerable size, the 

 cms is correspondingly wide and lies flush with the mesal surface. In Phoca the bulb 

 is relatively smaller and the cms has atrophied to scarcely more than a pedicle; it lies 

 deeply imbedded in the olfactory flsSure; it is removed 6 to 8 millimeters from the 

 mesal surface by a portion of the cortex which projects fully 5 millimeters beyond 

 the cms. 



The precribmm (anterior perforated space) is well developed and shows with 

 greater distinctness than in Gallorhinus. 



