114 KANSAS UNIVERSITY SCIENCE BULLETIN. 



infundibulum and posteriorly into the optic lobes. A slender 

 cavity also extends back into the pineal region. (Fig. 10.) 

 The walls of the optic thalami are relatively thick. 



The optic ventricles are continuations of the third ventricle 

 into the optic lobes. They correspond in shape to the rounded 

 external lines of the optic lobes. 



The cavity occupying the medulla, the fourth ventricle 

 (fig. 9, 4V), is joined dorsally to the union of the third and 

 optic ventricles. A plexus extends into it from the base of the 

 cerebellum and from the side walls, partially dividing it from 

 the cavity of the cerebellum. (Fig. 9, P; fig. 5, P.) The pos- 

 terior wall of the cerebellum is extremely thin, and it seems 

 that a great deal of readjustment takes place at this point as 

 the embryo passes into the adult condition. 



At the base of the cerebellum the fourth ventricle opens to 

 the exterior in the fossa rhomboidalis. (Fig. 9, I ; fig 5, I.) 

 The spinal canal joins the posterior end of the fourth ventricle. 



The cavity of the hypophysis is horizontally disk-shaped, 

 and in this stage is not connected with the main cavity of the 

 brain. 



The pineal apparatus also contains a cavity which does not 

 connect with the main cavity of the brain. It is peculiar in 

 having a very irregular shape and in possessing a number of 

 blind pockets, which may be seen in the diagrams of both the 

 vertical and horizontal planes. 



CRANIAL NERVES. 



The cranial nerves with their points of attachment and their 

 extensions as far as modeled are shown in the plates, so that 

 little more need be said concerning them. 



The crossing of the nerve tracts in the optic chiasma is 

 shown in a series of drawings (fig. 12) and a diagram rep- 

 resenting the mode of crossing of the nerves is also repre- 

 sented (fig. 13). The chiasma of Eumeces is almost iden- 

 tical in its mode of crossing with Lacerta, the European lizard. 



COMPARISON OF THE ADULT AND EMBRYONIC BRAIN. 



A glance at the shape of the embryonic brain shows that a 

 great many changes must take place in its shape as well as in 

 its size before it reaches the adult condition. (Figs. 14 and 15.) 

 The most evident changes are shown in fig. 15 by arrows. 

 The tendency of the whole brain is to assume a longer axis. 



