OF DENISON UNIVERSITY. 70 



position, and the superficial one spreads over the whc-le pyriform lobe. 



The next section (Fig. 8, Plate II,) taken behind the chiasm shows 

 the optic tracts collected on either side of the now distinct thalamus and 

 separated by the infundibuhim. The olfactory tract crosses the nar- 

 row third ventricle by a sudden curvature via the anterior commissure 

 which seems to be a genuine commissure of the olfactory and adjacent 

 sensory tracts. 



An important tract now first a]3pears. It consists of fibres passing 

 obliquely dorsad behind and ventrad to the commissure. Neither 

 upper nor ventral terminus appears in this section, but the fibres can 

 be traced ventro-laterad and caudad to form the descending tracts of 

 the fornix, as already seen in longitudinal sections, and cephalad and 

 dorsad until they unite the so called fornix nuclei of both sides by a 

 strong decussational band near the ventro-caudad border of the cal- 

 losum. We can not determine whether there is absolute continuity be- 

 tween all these fibres and the commissure of the hippocampus. The 

 latter is certainly chiefly made up of the fibres from the fornix, but it 

 also apjjears that some of the fibres from the hippocamjius are truly 

 commissural while, on the other hand, some at least of the fornix fibres 

 appear to terminate in the gray matter of the fornix nucleus or body. 



The farther course of the descending tract of the fornix has been 

 given above. We do not find evidence of the absolute continuity of 

 the fibres of this tract with those of the fasciculus of Viccj d'.Xzyr or 

 ascending fornix tract of Ferrier. 



The body or nucleus of the fornix adheres to the inferi<jr surface 

 of the corpus callosum, but there is no evidence of organic connection. 



Plate ,1, Fig. 8, illustrates a section near the front of the corpus 

 callosum. The fornix body has already become distinct from the 

 corpus striatum. The central tract of the olfactory nerve lies ventrad 

 and slightly dorsad from the line e, the external tract being near b. 



Plate II, Fig. 8, represents a section at the anterior commissure 

 The prominences of the fornix body are here cjuadrangular and medi- 

 anly give rise to tracts which pass caudad to the commissure. The 

 optic tract appears near the median line above i. IMate I\'. l'"ig. i. 

 exhibits the relations of the tracts descending from the fornix mu leus. 

 In sections immediately following, a very broad band of fibres con- 

 nects these two prominences and their extension also unites the ventral 

 surfaces of the hipjjocampus. Tnis belt of fibres has suffered the 

 same involution that the substance of the hii)i)ocampus has, and in 



