The origin of the Corpus Callosuni, a contrib. upon the Cerebral Coram, etc. 241 



anterior commissure, the fact that the larger division extends forwards, 

 in part at least, into the ventre - lateral region of the mantle seems 

 to place its homology with the pars olfactoria beyond doubt. The 

 discovery of the distinct smaller division {2)t) strengthens this view, 

 as opposed to that of previous authors, as it furnishes a tract which 

 we may homologize much more positively with the pars temporalis. 

 We may now inquire whether the Reptilian brain lends sui)port 

 to these observations upon the Amphibia. 



Clielonia. 



Among the Reptilia I have thus far been able to examine the 

 brains of the chelonia, Emys Europaea and Testudo Grace a. 

 The hemispheres are of a higher type than those of the Amphibia. 

 There is a great development of the brain stem, as in the Saurop- 

 sida generally, while the mantle and especially the inner wall is 

 comparatively thin. The temporal lobe is greatly developed. The 

 olfactory lobes are well distinguished from the hemispheres. 



The position of the cerebral commissure is quite different from 

 that in the Amphibian brain. They unite in an expansion of the 

 lamina terminalis slightly below and in front of the foramen of 

 Monro (fig. 19). This position is practically similar to that of the 

 anterior commissure and corpus callosum in the Monotremes, as far 

 as we can judge from Flower's figures (see woodcut), while the Am- 

 phibian brain, as we have seen, presents merely an advance upon the 

 fish type. The cheloniau brain shows even more clearly than the 

 Amphibian, the distribution of the upper bundle. The lower bundle 

 presents more difficulties. This is partly owing to the peculiar com- 

 position of the brain in which the nerve fibre courses are unlike those 

 either in the Amphibia or the mammalia. 



The upper bundle. As the reptilian brain is of a higher 

 type than the amphibian I anticipated finding the upper ))undle much 

 larger than the lower. As a fact it is scarcely if any larger, the 

 proportion being about 5:4. In the brain of a pigeon fledgeling I 

 found that the lower bundle is both larger and earlier developed 

 than the upper ; from this we may infer that the size of the upper 

 bundle is in proportion to the development of the inner mantle of 

 the hemispheres which in the Chelonia is somewhat reduced and in 

 Aves very strikingly reduced in comparison with the outer wall and 

 brain stem. 



