436 C. JUDSON HEKRICK 



their positions being indicated in the median dissection of the 

 brain shown in Fish's fig. 3 by projections of the choroid plexus 

 which lie within them. 



In Amphiuma (Muraenopsis) the pars ventro-medialis is also 

 feebly developed (Osborn, '83). There is no septum ependymale, 

 the brain being greatly flattened dorso-ventrally. This brings 

 the ventral border of the pars dorso-medialis far ventrad (fig. 23). 

 A small precommissural body is seen around the ventro-medial 

 angle of the lateral ventricle. The dorso-medial and dorso-lateral 

 parts are separated by a deep ependymal groove, while the boun- 

 dary between the two ventral parts is not so clearly marked. 



The 10 mm. larva of Diemyctylus viridescens (Mrs. Gage, '93) 

 in the matters here under discussion is very similar to the 17 mm. 

 larva of Amblystoma, and the adult Diemyctylus to the adult 

 Amblystoma. 



In the brain of the adult Plethodon glutinosus the figures of 

 Dodds ('07) show relations of the walls of the hemisphere which 

 .are similar in essential points to those of adult Amblystoma. 



In none of the species which I have hitherto described do the 

 cells of the nucleus medianus septi extend dorsally above the 

 interventricular foramen. 



Through the kindness of Dr. J. B. Johnston I have examined 

 sections of the brain Cryptobranchus and find the relations very 

 similar to those of Necturus. The nucleus medianus septi is 

 larger than in Amblystoma and extends for a short distance back- 

 ward dorsally of the interventricular foramen. 



I have studied the conditions in adult Necturus and in larvae, 

 the latter from specimens in the Harvard Embryological Collec- 

 tion. Kingsbury ('95) has given an excellent series of figures of 

 the adult brain, and comparison of these with the preceding figures 

 of adult Amblystoma will render a detailed discussion of the con- 

 ditions in Necturus unnecessary. 



In adult Necturus the septum ependymale has become massive 

 except for a very short remnant immediately rostral to the inter- 

 ventricular foramen. The nucleus medianus septi is moderately 

 developed in the ventro-median part of the hemisphere. As we 

 approach the lamina terminalis, it is divided into a ventral and a 



