Humphrey, Brain of the Snapping Turtle. 107 



trace the fibers of the precommissure to their distribution. The 

 dorsal bundle extends cephalo-dorsad in a curved course. 

 When about the level of the dorsal margin it divides, one large 

 branch turns sharply caudad, passes near the dorsal margin of 

 the porta and is distributed to the caudo-mesal cortex of the 

 cerebrum. I consider this to be the homologue of the commis- 

 sura cornu ammonis of Osborn and in all probability it is a part 

 of the callosum. Its distribution is as shown by Osborn in 

 Emys Enropca (59, Fig. 18). The cephalic branch of the 

 commissure spreads out over the mesal cortex, and is the hom- 

 ologue of the callosum of Herrick (Fig. 36.) 



Similar relations exist in the brain of Chelone and Chtys- 

 eniys. In the latter the common bundle projects more sharply 

 into the aula at the meson and is almost freed from the terma. 

 In Chelone the common bundle was placed farther ventrad than 

 in other forms observed (Fig. 7.) The presence of descending 

 fornix tracts was not proven although in Chelydra there is evi- 

 dence of their presence. The prosencephal of reptiles has been 

 so thoroughly studied of late by Edinger, Herrick, Meyer and 

 others, that I have made no attempt at the almost hopeless task 

 of adding to the knowledge of that interesting region. 



Summary. 



1. The brain of Chelydra is probably the most simple of 

 the Reptilia. While it approximates the Amphibia in external 

 simplicity, internally it contains representatives of nearly every 

 structure of the higher types of brains. 



2. The sulci of the metencephal are formed by the apposi- 

 tion of cylindrical fiber columns and owe their depth and loca- 

 tion to the position of the columns. 



3. The metacoele is continued caudad of its union with the 

 myeloccele and dorsal furrow and is demarcated from them with 

 unusual clearness. 



4. A distinct pocket exists in the metatela in the region of 

 the metapore of some other animals. This pocket is extremely 

 thin-walled in the late embryo and the possibility exists that a 



