Herrick, Morphology of Brain of Bony Fishes. 347 



"If we assume that the sensory peripheral fibres termi- 

 nate in free branches in ckisters of gray matter, and that 

 from the cells of such niduli new nerve fibres arise and con- 

 duct the excitement centrad, the conditions for determining 

 central tracts and centres are satisfied." 



In 1854 Kolliker described the olfactory fibres of the ox 

 and sheep as tubes with nucleated contents. 



The above view, which is theorectlcally so probable, 

 receives considerable confirmation from the facts to be pre- 

 sented, as well as a partial new interpretation. 



A glance at Fig. i, Plate XXIV, will show that the radix 

 lateralis passes directly and without interruption to a special 

 caudo-ventrad projection of the cerebrum, already identified 

 upon topographical grounds as the homologue of the hippo- 

 campus (see previous paper of this series). There the fibres 

 end near a special zone of cells. Entad of this specific homo- 

 logue of the hippocampal cells a tract of non-medullated 

 fibres seems to arise, which passes cephalo-ventrad and 

 crosses to the opposite side immediately caudad of the callo- 

 sum. This fibre tract can be nothing else than a rudimentary 

 hippocampal commissure, together with the fornix. That 

 the latter structure is included is shown by the fact that a 

 small branch passes to a bifid cellular mass projecting into 

 the ventricle from the caudo-ventrad aspect of the callosum; 

 in other words, an unmistakable homologue of the body of 

 the fornix. To complete the identification, we think we 

 find a small tract extending from the latter to the thalamus. 

 The unmeduilated nature of the fibres makes the study 

 diflicult. 



The radix mesalis pursues an altogether different course. 

 After entering the post-rhinalic region of the cerebrum, this 

 cylindrical bundle passes caudo-mesad, and, after dividing 

 into a number of smaller tracts, forms a part of the pra^com- 

 missural system. Nevertheless, this band is distinct from 

 both the true praecommissura and the axial commissure or 

 decussation beneath it. 



