DORSAL VENTRICULAR RIDGE 



495 



Fill, '.i CMirysiMiiys I'lnl.ryo of 17 iiiiii. Medial view of a iiiodol of tlu" rinlit 

 hemisphere. The narrowing of the interventricular foramen seems to have 

 taken place from above downward on account of the expansion of the hippo- 

 campus and general jiallium. The white area labelled r.h., is the cut surface of 

 thcprimordium hippocam])! in the median plane. The thin portion of the medial 

 hemis))here wall which will form the choroicF fissure and plexus is l)ounded hy a 

 white line. 



rig. 4 Same model as figure 3, with the thalanuis. hippocampus antl primor- 

 dium hijipocampi removed. The lateral wall of the ventricle shows the dorsal 

 ridge hounded ijelow hy the deep middle ventricular groove as described in the 

 text. The dorsal groove is shallow. There is no evident boundary between the 

 dorsal ridge and the pallial thickening at the rostral end. 



Fig. 5 Chrysemys, 28 mm. Lateral view of a model of the right hemisphere. 

 Note the great elongation of the pj-riform lobe in the caudal pole as compared 

 with the condition in figure 1. With regard to the exposure of the corpus striatum 

 on the lateral surface, compare figures 1 and 5 with the figures in '15 b. 



THE JOURNAL OF COMPARATIVE NECROLOGY, VOL. 26, NO. 5 



