Herrick, Btain of Certain Reptiles. 131 



ad of the post-commissure. The niduli in this case simply re- 

 main undifferentiated from the ventricular gray, though potential- 

 ly and functionally present. (Plate XVIII.) 



TJie diencepJialon and mese7icephalon of Utodela constitute 

 one continuous segment interrupted only by the post-commis- 

 sure. It is probable that the most diagrammatic representation 

 of the segments in question could be secured by generalizing 

 the relations as they exist in Menopoma or Necturus, which are 

 essentially similar. The drawings and descriptions of Osborn 

 have made us sufficiently familiar with the external form and 

 general relations. It will be desirable, however, to examine a 

 series of horizontal sections beginning from the dorson in order 

 to get a comprehensive view of the structures. 



The most dorsal section shows three structures ; i. The 

 preparaphysis (often mistaken for the epiphysis) consisting of an 

 enormous expansion of the preplexus dorsad of the aula. It is 

 composed of a large irregular central chamber with complicated 

 peripheral diverticles of a tubular or irregular character around 

 which blood vessels anastomose. The form is, in general, nearly 

 spherical. 2. The post-paraphysis or " polster " — a dorsal ex- 

 pansion of the third ventricle with irregular projections ectad 

 and entad. The diplexus is a derivative of this system. 3. 

 Immediately caudad of this, but separated from it by the supra- 

 and habena-commissures is the epiphysis, which consists of an 

 irregular aggregate of vesicles connected with the third ventricle 

 by a narrow opening. The supra-commissure system consists 

 of two distinct bundles, a small cephalic and dorsal and a larger 

 caudal and ventral bundle, a small branch to the epiphysis from 

 the former was doubtfully identified (parietal nerve.) The ven- 

 tro-caudal bundle passes laterad of the smaller commissure and 

 comes to lie ectad and cephalad of it, forming the main body of 

 the commissure, while the supra-commissure proper continues 

 directly ventrad, forming (?) a part of the optic system. (?) Fig. 

 I, Plate XVIII, illustrates these conditions. Fig. 2 is the re- 

 gion of the supra-commissure, showing the several tracts. From 

 the habena as well as what seems to be the locality of Meynert's 



