94 THE VOYAGE OF H.M.S. CHALLENGER. 



the inner aspect of the crura cerebri. The fourth nerves had been torn away in the 

 removal of the brain. The hypophysis or pituitary body was situated behind the optic 

 commissure and between the third pair of nerves. It was about the size of a small hazel 

 nut and small on its surface, though a shallow depression on each side indicated a 

 division into an anterior and a posterior lobe. It was hollowed out internally into a 

 cavity continuous with the infundibulum. On raising the pituitary body the tuber 

 cinereum was seen surrounding the base of the infundibulum. The crura cerebri were 

 short and flattened on the ventral surface. 



Convolutions and Sulci. — In entering on a description of the sulci and convolutions 

 of the brain, either of the Carnivora or of the suborder Pinnipedia, one of the difficulties 

 experienced by the anatomist is the selection of the terms to be employed. The literature 

 of the carnivorous brain is extensive, more especially in recent years ; and as many 

 authors have employed their own terms without much reference to the nomenclature 

 adopted by other writers, it is sometimes difficult to decide which name should be 

 selected in description. After some consideration I have thought it advisable not to 

 limit myself to the terminology of any single anatomist, but to select from the writings 

 of various authors such of the names as seemed to be most appropriate. 



Each hemisphere of the cerebrum of the Elephant Seal was rich in convolutions and 

 intermediate sulci. 



The Sylvian fissure, fissure of Sylvius (s). This was the largest sulcus, and com- 

 menced on the base of the brain in the Sylvian fossa, situated in the region of the 

 locus perforatus anticus. It passed almost transversely outwards to the side of the 

 hemisphere, and was then continued upwards and backwards for 32 mm. on the side of 

 the right hemisphere, but not so far on the left, and from it an offshoot ascended almost 

 vertically for 13 mm. The suprasylvian fissure sprang out of it, and seemed as if it were 

 an anterior branch of bifurcation. 



The Crucial fissure (Leuret), fissura cruciata (c). 1 This fissure was not visible in the 

 norma verticalis, for it was situated so far forward that the brain had to be looked at 

 from the front in order to see it, so that it corresponded with Leuret's description of its 

 position in the brain of the common Seal. In the Elephant Seal it extended at first 

 obliquely and then almost transversely outwards for 30 mm. from the mesial longi- 

 tudinal fissure. It formed a well-marked feature in this region of the brain, and a large 

 sigmoid gyrus (sgc) was bent around its outer end. 



Bounded above and in front by the crucial fissure, and behind by the basal part of 

 the Sylvian fissure and fossa and the locus perforatus anticus, was a well-defined area on 

 the hemisphere, which rested on the sphenoid and frontal bones where they formed 

 the roof of the orbit. This supraorbital area 2 obviously corresponded in position to 

 the orbital surface of the frontal lobe in the human brain, and like it was subdivided 



1 Frontal fissure, Owen. 2 Supraorbital convolution, Leuret ; Orbital convolution, Langley. 



