PISCES. 



BRAIN. In an osseous fish, as the cod, the anterior lobes of the brain are small ; 

 the optic lobes are much larger. The ventricle is continued from the anterior lobes ; it 

 passes under a commissure between the optic lobes into them, and under the cere- 

 bellum to the calamus scriptorius. The ventricular cords on its floor are not so 

 distinct as in the skate. The cerebellum consists principally of a middle lobe, the 

 anterior point of which extends into the ventricle of the optic lobes : it has a very 

 small ventricle. At the base the anterior lobes are again partly seen, and the small 

 olfactory nerves proceeding from them. The pituitary gland is also seen, and the large 

 mammillary eminences ; and behind these is the continuation of the oblong medulla, 

 which is very slightly different from the spinal cord. In a cartilaginous fish, as the 

 skate, there are similar parts ; but the anterior lobes of the brain are much larger than 

 in the cod, in proportion to the optic lobes ; the ventricular cords are more distinct. 

 The cerebellum is larger ; it has a larger ventricle. At the base the large anterior 

 lobes of the brain are again seen, and smaller mammillary eminences. The oblong 

 medulla and spinal cord are not very different from the same in the cod except in 

 size. In the cod the small olfactory nerve proceeds from a small anterior lobe, and 

 forms a bulb or ganglion over the nose, from which nerves pass to the membranous 

 plaits ; in the skate it is larger, and proceeds from a much larger lobe : it forms a 

 larger ganglion, and its termination is similar. In the cod the optic nerve is larger, 

 and proceeds from the optic lobe and mammillary eminence, and decussates its fellow 

 after its origin ; in the skate it is similar, but smaller, and does not decussate its fellow, 



