The origin of the Corpus callosum, a contrib. upon the cerebral comm. etc. 531 



Jahrb. Band XIL pag. 223 — 251) are now fully elucidated and 

 much new information has been gained. In the brain of Tropido- 

 notus, the common snake of England, I happened upon the very 



Transverse section of the brain of Rana esculeuta, 

 through the cerebral commissures. 



condition of the cerebral commissures in the Reptilia which I an- 

 ticipated would be found viz : a completely developed anterior com- 

 missure, as well as descending tracts, in connection with the corpus 

 callosum, which probably represent the fornix. 



Ophidia. 



In Tropidonotus natrix the cerebral hemispheres are broad 

 and deep. They taper rapidly forwards and pass into the long nar- 

 row olfactory lobes. The lamina termiualis extends obliquely u})- 

 wards and is proportionally of greater vertical extent than in the 

 chelonia. The cerebral commissures are not compressed into a single 

 bundle in the median line as in the chelonia but traverse the la- 

 mina terminalis in three distinct groups placed above each other. 

 The two lower bundles represent the divisions of the anterior 

 commissure (figs. 20 and 21). Their distribution, as seen in 

 horizontal sections, corresponds with the typical development of 

 this commissure, as observed in the mammalia. This brain however 

 presents two exceptions to the usual relations of this commissure, 

 in that, first, the two parts are quite distinct in the median line, 

 and, second, the pars temporalis is dorsal to the pars olfactoria. 

 Fig. 21 is an oblique section in which the two divisions lie in the 

 same plane. The pars temporalis is composed of fine fibres and 

 arches upwards and backwards around the cortex of the temporal 

 lobe, its fibres passing inwards to the adjacent cell layer. The pars 



