l6o JOURNAI. OK CoMPARATlVK NeUHOLOGY. 



point in front of the foramen of Monro in the sturgeon brain, 

 shows that a cavity clothed by tela choridea (or pallium) 

 extends cephalad along the dorso-mesal surface of each olfac- 

 tory lobe. This cavity is of great morphological importance; 

 part of its walls are modified to form a plexus, and it comes 

 into direct communication with the aula. The surface of the 

 lobe bordering is, like other ventricular surfaces, covered 

 with epithelium. The cellular structure is also unlike that 

 of the remainder of the lobe. It seems unqestionable that 

 this space is homologous with the cavity of the lateral ven- 

 tricle, which is not roofed over with nervous matter, but has 

 merely the tela or pallium. These two ventricles become con- 

 fluent cephalad to the openings of the olfactory lobes, but a 

 partial division, by a depending loop corresponding to the 

 dorso-mesal walls of the mantle, may be traced back of that 

 point. From the ventral extension of these median walls 

 two arms, forming with them an irregular inverted Y, pass 

 laterad nearly to the ectal thickened walls of the hemisphere, 

 shutting off a median aula from the lateral ventricles, with 

 which the former is connected by large portae. It is from 

 the ventricles thus bounded, and not from the median cham- 

 ber, that the olfactory aqueduct springs. 



The development of nervous matter in the cerebrum 

 is greater relatively in the gars, therefore the membranous 

 portion of the mantle is greater in Scaphirhynchus. In Lepi- 

 dosteus the ventricle gives oft^ two spurs in the median por- 

 tion delimiting a body somewhat resembling the corpus len- 

 ticulare of the striatum. The posterior cornu sweeps back 

 of the crura and then circumscribes the ventral and ectal 

 portions of the cerebrum, finally meeting the dorsal exten- 

 sion of the ventricle, enclosing a large occipito-basal lobe 

 much as in reptilia. The extent of the ventricle may be most 



combined with the hemispheres of the br.iin ; .tiuI although I h.ive not discovered in the 

 species examined by me the ventricles in those bodies described by Wilder, yet I do not 

 doubt that in other species they may exist." 



