Fish, Brain of the Fur Seal. 6i 



pearance at the surface of a long continuous fissure. By 

 separating its walls or "sounding" its depth the true state of 

 affairs is easily perceived. The presence of a shallow whether 

 it be near or at a distance from the end of a fissure would seem 

 to indicate that at some time during development this shallow 

 has been or will be represented at the surface and separate two 

 independent fissures. 



CALLORHINUS URSINUS. 



Cranial N^en'es. The cranial nerve roots of Callorhinus are 

 well developed and need no special comment. In the case of 

 the optic nerves we do not find the X-shaped chiasma as in 

 Phoca, but the nerves run parallel to each other for a short 

 distance from the chiasma before diverging toward the eyes. 



The third pair or oculomotor nerves have a straight lateral 

 direction from their apparent origins, but at the lateral border 

 • of the hypophysis they bend abruptly upon themselves and 

 proceed cephalad forming a very distinct right angle. 



The olfactory lobes are fairly well developed. 



Fissures. No special mention will be made of the gyres 

 (convolutions). These are naturally formed b}^ the fissural de- 

 pressions and it is believed that a careful description of these 

 furrows will by implication include that of the gyres sufficiently 

 for our present purpose. 



The olfactory fissure is completely hidden by the olfactory 

 crus and bulb ; when these are removed a shallow fissure is ap- 

 parent which becomes deeper toward the base of the lobe. 



Forming the lateral boundry of the olfactory lobe is the 

 rhinal fissure which passes in a caudo-lateral direction to the 

 Sylvian. An apparent continuation of the rhinal from the Syl- 

 vian is known as the post-rhinal fissure. It extends in a meso- 

 caudal direction for a centimeter and a half, stopping just short 

 of the cleft between the cerebrum and the cerebellum. A care- 

 ful examination of the postrhinal shows that it has no connec- 

 tion whatever with the rhinal but is continuous, superficially at 

 least, with a subfissure (postica ?) lying in the caudal wall of the 

 Sylvian. 



