21 CENTRAL NERVOUS SYSTEM. 



atively of greater volume, and the upper and middle ventricular walls 

 thinner, in the latter animal. 



In the box turtle, Plate XC. the corpus striatum is seen to be a- 

 bout as large, proportionally, as in saurians. This plate also shows the 

 manner in which the lateral ventricles communicate with the third ven- 

 tricle. The upper and middle walls are thin, and their zone of cells 

 lies nearer the surface of the ventricles than in saurians and ophidians, 

 in this respect resembling batrachians. 



Plate LXXXIX. from a transverse section gopher snake made 

 through the posterior part of the optic chiasm, shows the third ventricle 

 and optic tracts with the cerebral lobe of one side, and its large ventric- 

 ular protuberance ; downward extension of the same, and tendency of 

 the upper wall towards symmetry of curvature. 



The essential structure of the choroid plexus, and its relation to the 

 walls of the ventricles are seen in Plate XCVIII. 



THE OLFACTORY LOBES. 



THE olfactory lobes of the frog, as seen in cross section, may be taken 

 as a fair type of these organs in all the species. The olfactory nerves 

 are underneath the lobes, in this batrachian, Plate XCV. while in 

 the tailed varieties, they are on each side. 



A LATER series will include several species not mentioned in the present 

 work, and an effort will be made to illustrate the minute anatomy of 

 certain parts of the central nervous system, such as the optic thalami 

 and hypophysis cerebri, which, from want of preparations suitable for 

 photography, are now omitted. 



