132 Cincinnati Society of Natural History. 



tudinally-perpendicularly. From these the effort was made to spa- 

 tially reconstruct the several organs and trace the course of tracts. 

 The accompanying drawings are nearly all made with the aid of the 

 camera lucida, and the effort was made to exhibit only what 

 appears in the actual section studied, and to copy, as far as consist- 

 ent with the small size of the reproductions, the appearance of the 

 section. Thus, instead of generalizing tracts or representing 

 nuclei by a few exaggerated cells, the attempt was made to present 

 as nearly as could be the texture seen with the power used. No 

 liberty has been taken with the outline of sections, so that where 

 they were somewhat oblique the lack of symmetry was faithfully 

 copied. 



In no class of vertebrates is our knowledge so limited as in the 

 Reptilia, and, for this reason, the writer labors under some dis- 

 advantage. It can not be hoped that the entire range of literature 

 has been examined, though great effort was made to secure all 

 important memoirs. 



We have a very accurate description of the topography and 

 external form of the alligator brain by Rueckhard.* 



It will, therefore, be unnecessary to go into details of this sort. 

 The difference in age between our specimens and those of Rueck- 

 hard may account for discrepancies. The reader is referred to the 

 figures of the entire brain on Plate VII for details. 



I. — Gross Anatomy. 



1. The Rhinencephalo7i. The olfactory portion of the fore-brain, 

 in this stage, projects beyond the hemispheres by about the com- 

 bined length of the hemispheres and optic lobes, and forms a 

 double, clavate body. The two lobes, though closely appressed, 

 are quite distinct. The lumen of the crura olfactoriais continuous 

 with the cerebral as well as the rhinencephalic ventricle, and, 

 indeed, there is no sharp line of demarkation. The minute struc- 

 ture differs but slightly from that of mammals. 



Wiedersheim says (Comp. Anat., p. 146) " Olfactory lobes seem 

 to be absent in crocodiles only," a statement evidently based on 

 hasty observation. 



2. Prosencephalon, as seen from above, is broadly oval, and is 

 somewhat emarginate behind for the reception of the optic lobes. 

 A cross section near the front of the hemispheres shows the greatest 



*Rabl-Rueckhard, " Das Centralnerven-system des Alligators," Zeit- 

 schriftfuer wissenschaftliche Zoologie, Bd. XXX, p. 336, 1878. 



