84 BULLETIN OF THE LABORATORIES 



of the absence of the callosum, they may serve as a type for compari- 

 son. Beginning at a region cephalad of the union of the two hemi- 

 spheres (Plate A, Fig. 3.) we observe that the cortex at the splenial 

 fissure becomes very narrow and dense and the cells acquire much the 

 appearance of those of the hippocampus. The outer neuroglia layer is 

 thickened and the peripheral fibre zone is collected in small tracts. 

 These tracts, some of the fibres of which may represent the mesal 

 olfactory tract, are thus described in my notes. "A tract which 

 arises ventro-mesal near the crus of the olfactory (exact locality inde- 

 terminate) passes caudo-dorsad within the cortex. The several small 

 bundles emerge into the neuroglia zone and before the formation of a 

 deep splenial fissure have attained a position dorsad to it. Thence 

 they pass caudad and are carried entad by the deepening of the 

 fissure and are last seen in the region of the anterior commissure ap- 

 parently terminating in cells of the uncinate gyrus." 



Entad, a strong tract derived from the cells of this region passes 

 meso-ventrad of the tract mentioned, is separated from the corpus stri- 

 atum by a spur of the ventricle, and is filled with thickly scattered cells. 

 An oblique band of cells passes from the ventricle ventrad toward the 

 meson and seems a continuation of the irregular chain of cell-clusters 

 characteristic of the pseudo-cortex of the ventral region. On the oth- 

 er side of the ventricle opposite the dorsal end of this cell-series is the 

 cephalic branch of the anterior commissure. The limits of the gyrus 

 fornicatus and uncinatus are more or less arbitrarily determined in 

 mammalia. Ranney considers the posterior margin or splenium of 

 the callosum the point where the former passes into the latter. In the 

 present case, however, there being no such guide, we are forced to de- 

 pend upon morphological modifications of the organs themselves. 

 The gyrus fornicatus arises cephalad by the fold induced by the sple- 

 nial fissure already described. It may be traced cephalad nearly to the 

 olfactory. The uncinate gyrus is a second fold which appears as the 

 two hemispheres fuse. (Plate A, Fig. 4.) The free dorsal margin is 

 outwardly folded and at the same time ''faulted" by being slid some- 

 what laterad as if by the agency of the thalamus wedged between the 

 hemispheres. The fornicate and uncinate gyri are curved in opposite 

 senses and related to each other somewhat as are tiles on a roof. In 

 speaking of the uncinate gyrus as the free portion of the median cor- 

 tex it must be understood in a limited sense, for the mesal margin 

 passes into the plexus and tela and ultimately forms the connection 



