He u KICK, Morpliology of Brain of Bony Fishes. zi-\ 



in texture and dilated with fluid. Immediately caudad of the 

 saccus vasculosus a large blood-vessel enters the brain in the 

 median line. This is always present and seems to represent 

 the area perforata posterior of higher brains. The broader 

 end of the cinereum is directed cephalad and is indented in 

 the median line by a deep sinus extending to its centre. This 

 point is the most ventral projection of the cinereum, and 

 from it the infundibulum passes out into the hypophysis. 

 This appendage is slightly ovoid, with the larger end 

 directed cephalad, 4.5 mm. long by 3.5 mm. wide and high. 

 The stipe is filiform, slightly thicker at the base and attached 

 to the body of the hypophysis at a point about one-fourth of 

 the distance from the caudal end of the latter. The hypo- 

 physis is solid, and of a uniform texture. 



Mesencephalon. — The portion of each optic lobe which is 

 exposed is ovoid, with the larger end directed cephalad and 

 the long axis passing obliquely dorso-caudad. The two 

 lobes are widely divaricated by the cerebellum. The roof of 

 the mesencephalon is depressed, thin, and devoid of cellular 

 elements, except internally in the tori longitudinales 

 ("fornix" of authors) adjacent to the ventricle. The 

 mesencephalon does not reach the ventral surface of the 

 brain at any point. In this region, cephalad, that surface is 

 entirely occupied by the hypoaria, while the portion caudad 

 of the hypoaria is to be considered a forward extension of the 

 medulla, as in higher animals. 



Epencephalon. — In this group of fishes the cerebellum is 

 the most characteristic feature. It consists of two major 

 divisions, one external and one internal. Both are well 

 developed, the former to an unusual degree. The whole mass 

 of the first division is folded upon itself at an angle of 90°, 

 thrust cephalad, and closely appressed to the subjacent optic 

 lobes and hemispheres. The entire extent of the fourth 

 ventricle is thus exposed, in striking contrast to the brains of 

 most other fishes. As viewed from above, the cerebellum is 

 nearly rectangular, with a lateral expansion caudad, and it 



