24 JorRXAI. OF COMHARATIVK NEUROLOGY. 



and its fibres are not deeply stained, being perfectly distinct 

 from both the preceding. They pass caudo-laterad and 

 somewhat dorsad to the occipito-basal lobes, forming a 

 tract along the caudad margin of the latter and arching 

 over the peduncular tracts. It is from the lateral portion 

 of this tract that the tracts apparently homologous with the 

 descending pillars of the fornix arise. These fibres doubt- 

 less spring from the occipito-basal lobe and divaricate 

 from the commissure of those lobes and then pass entad to 

 the peduncles in their course to the homologue of the mam- 

 millare. 



It will be seen that the fornix is a much more simple 

 body than in higher vertebrates. Instead of two distinct 

 portions with a cellular mass interposed near the median 

 line, we have a continuous tract on either side from the 

 occipital region to the mammillare. The nature of the 

 tract ascending from the ventro-basal region to beneath the 

 callosum in the alligator is left doubtful. 



The complete differentiation of the commissural system 

 in serpents is no doubt due to the great comparative com- 

 plexity of the brain as a whole, and especially of the oc- 

 cipito-basal lobe and the greater extent of the free occipital 

 cortex. 



It should be added that the above description of the 

 course pursued by the several branches of the anterior com- 

 missure leaves much to be desired as to the exact con- 

 nections in the olfactory. There is. as already stated, a 

 large mass of cortex upon the lateral and dorsal parts of the 

 olfactory crus. It is from this that the strong latero-ventral 

 tract originates, which then passes caudad, laterad, and 

 dorsad beneath the cortex to a point as far caudad .is the 

 termination of the middle pra;commissural tract. There 

 seems to be no direct connection with the last named or 

 the peduncular bundles. It also appears that the cephalad 

 branch of the anterior commissure enters the cortex of the 

 crus rather than the specific olfactory substance. The only 



