PLATE 1 



EXPLANATION OF FIGUKES 



The reference letters for all figures are found on page 513. It is impossible 

 to portray all the topography of the region around the foramen interventriculare 

 by means of drawings. For aid in orientation, the position of the principal 

 landmarks is indicated on the models as follows: the taenia fornicis by a line of 

 dashes; the velum transversum by a line of crosses; the taenia thalami by dots; 

 and the di-telencephalic groove by dots and dashes alternating. The cross 

 sections will also aid. On figures 22 and 23 the positions of the sections are 

 indicated by arrows. Since the models are tilted, the arrows indicate accurately 

 only the points where the sections cross the lateral telencephalic plexus. 



20 Median view of the fore brain of a 5.1 mm. embryo of Chrysemys marginata. 

 Embryo 1 a. X 50. 



532 



