FISHES. 43 



saturated with a fatty matter mostly in a fluid state. In younger 

 fishes, however, the brain is relatively larger, and fills the cranial 

 cavity in a greater degree than in older individuals. 



In breadth the brain exceeds the spinal cord but slightly, is 

 flat and elongate, and consists of eight lobes partly in pairs, partly 

 unpaired, lying behind one another. The unpaired part that lies in 

 front of the medulla oblongata above the fourth ventricle, corresponds 

 to the lesser brain or cerebellum; and, however various the opinions 

 of different writers on other points, here there is the most perfect 

 agreement. Internally this part is hollow, for the fourth ventricle 

 at its upper part extends into it. In front of this cerebral mass lie 

 two convex bodies, hollow internally, which in bony fishes consti- 

 tute the largest division of the brain, whilst in the cartilaginous they 

 are smaller. CAMPER, CUVIER, and amongst the latest writers 

 GOTTSCHE, compare these parts with the hemispheres of the larger 

 brain (cerebrum), whilst others place them on a par with the corpora 

 quadrigemina of man ; HALLER regarded them as the thalami ner- 

 vorum opticorum. In the bony fishes there lie in the interior of 

 these parts and behind, two or four small round tubercles of grey 

 substance, which are wanting in cartilaginous fishes. In these last 

 the two convex bodies are also smaller, and in front of them lies an 

 unpaired hollow eminence, open above (lobus ventriculi tertii), which 

 in the bony fishes does not appear as a distinct part. The anterior 

 division of the brain in the osseous fishes is formed of two conical 

 parts, not hollow internally, united by a commissure; from this 

 division arise the long olfactory nerves (the first pair of nerves), 

 issuing from the inferior surface, but fortified in most bony fishes by 

 a swelling at the anterior extremity of these lobes, or by two such 

 in Murcena. In the Plagiostomes these anterior lobes, broad and 

 hollow within, are united with one another. On the inferior 

 surface of the brain the hypophysis or glandula pituitaria, some- 

 times attached to a long pedicle, is seen, near to which on each side 

 lies an oval or kidney-shaped eminence (the lobi inferiores, the 

 tubercula reniformia of HALLER 1 ). 



1 The origins of the optic nerves pass along the outside of these parts, and the third 

 pair of nerves springs from their posterior margin. They are usually compared to the 

 corpora candicantia of the brain of mammals, to which notion, however, well-founded 

 objections have been raised by CuviEB. It were more prudent to regard them, with 

 GOTTSCHE, as special parts peculiar to the brain of fishes. 



