Notes upon the Brain of the Alligator. 145 



ventricle is concave toward the surface, and separates a thick por- 

 tion of the mantle, corresponding in some respects to the anterior 

 portion of the amnions horn. Its cellular elements resemble those 

 of the adjacent parts of the axillary lobe. 



A very noticeable layer of large flask-cells occupies the median 

 part of the median mantle segment. These cells, corresponding 

 to cerebro-sensory cells of higher animals, have their apical proc- 

 esses almost uniformly peripheral, and from the basal blunt 

 extremity fibres can be traced to a union with the tract along the 

 ventricle. The course of the apex fibres can not be traced because 

 of the obliquity of the cell axis. As the layer is traced to the dor- 

 sal surface, cells of the other type suddenly appear. These multi- 

 polar pyramids are somewhat larger, have peripheral apex-processes, 

 but are apparently directed in a direction contrary to the previous 

 set, as determined by focusing. This type of cell-structure extends 

 entirely around the mantle, the cells becoming parallel to the sur- 

 face in the thinner portions (some doubt remains as to the existence 

 of lateral flask-cells). The superficial part of the mantle is occupied 

 by fibre tracts, apparently extending longitudinally. Near the 

 ventral surface are gathered great masses of small multipolar 

 angular cells, which were supposed to be related to the .olfactory 

 fibres in some way. 



Passing to the thalamus portion of this section (Plate VIII. , 

 Fig. 9,) we notice that at this point the peduncular fibres diverge 

 into the hemispheres, the ventral column passing directly forward 

 and seeming to afford outlet for the motor cells of the dorsal sur- 

 face. The upper or descending tracts radiate largely to the axial 

 lobes. A pair of median prominences from the peduncles here 

 arise to meet the descending median portion of the mantle, as best 

 seen in longitudinal section (Plate VIII., Figs. 10, 100.; Plate IX., 

 Fig. 8). 



A large number of fibres collect in the thalamus from the basal 

 parts of the prosencephalon ; these cross the peduncular bundles 

 (Plate VIII., Figs. 10, 100., tr. t.). The fibres of the taenia thalami 

 (t. th.) begin to collect to form a bundle just exterior to the pedun- 

 cular tracts. This bundle passes backward (Plate IX., Fig. 9,) 

 and crosses to the thalamus (Plate XV., Figs. 4, 5 and 7) 

 and ascends the latero-frontal aspect of the thalamus to the region 

 of the superior commissure (Plate VIII., Figs. 11-16). The source 

 in the cerebrum of this tract has not been made out with certainty, 



