Bawden, Nose and Jacobsoris Organ. 127 



ical deviation in its course, while the fibres of radix mesalis aris- 

 ing from the median aspect of the pero pass dorsad of the cal- 

 losum when the latter is present as striae Lancisii to the hippo- 

 campus, and in the absence of the callosum (opossum) directly 

 dorsad to the gyrus fornicatus. Into and through the anterior 

 commissure and thence possibly to the hippocampus pass also 

 the fibres of the third bundle, the radix entalis. This is the 

 bundle which arises from the pes proper and in no case appears 

 to enter into connection with the olfactory cells. 



In the lower types, as the fish, there is only a rudiment 

 which can be homologized with hippocampus of the higher 

 forms. This homology has been traced by following the course 

 of the radix lateralis as it passes in the fish to this point. In 

 the higher types this is seen to be more distinct, while in rep- 

 tiles the typical folds of the hippocampal gyre begin to assume 

 their characteristic complexity. In mammals this folding be- 

 comes exceedingly complex, thus making the tracing of the 

 fibres from the olfactory lobe very difficult. The lobe in the 

 occital region of the cerebrum in the brain of reptiles which 

 contains the undoubted homologue of the hippocampus is called 

 by Edinger the ammon cortex. A comparison of the reptiles 

 with the opossum and rodents in general shows that the only 

 difference lies in the extreme complexity of the relations in the 

 higher types which obscures the homology. The problem now 

 is to trace the three radices back to the hippocampal region in 

 all these types and completely homologize these different parts ; 

 to explain the relative position of these bundles, accounting for 

 their migration and perversion by determining, among other 

 things, at just what point lies the evolutionary front of the head. 

 Another point of interest is the fact that recent investigators 

 have shown that the first centres of the olfactory nerve lie in the 

 pero of the bulb, and that from this point there migrate inward 

 nerve filaments which come into connection with out-going 

 fibres from the cortical centres. Thus the fibres connecting 

 the bulb with the cortex acquire a new significance and may be 

 homologized with the projection or irradiation fibres of the op- 

 tic centres which connect with the occipital cortex. 



