Herkick, Morphology of Nervous System. 167 



of the cerebrum. These latter are the largest and most 

 characteristic cells of the cerebrum, being fusiform or multi- 

 polar in outline. Without attempting any special hom- 

 ologies of the regions indicated with the lobes already 

 described in the cerebrum of reptiles, it becomes at once 

 obvious that there is a great similarity in the disposition of 

 cellular elements. The cephalo-lateral aspects contain pyram- 

 idal cells, the ventro-median fusiform, while the interior of 

 the axial lobe contains a paraxial aesthesodic variety. It 

 would appear, then, that regions corresponding to the 

 parietal lobes of Sauropsida exist in fish brains. That these 

 regions of pyramidal cells are motor, is farther indicated by 

 the strong tract arising in this neighborhood. 



Caudad to the section just described the thalamus expands, 

 and a pouch of the third ventricle is formed above the chiasm 

 with its opening caudad. At the chiasm the ventral walls of 

 this supra-chiasmic fossa are driven laterad and become filled, 

 next the ventricle, with densely-packed cells. In passing 

 caudad the basal portion of the cerebrum gradually becomes 

 more distinct, until it attains a measure of independence and 

 is finally overarched by a diverticle from the lateral ventricle. 



By reason of its connection with the olfactory, and its 

 position, this lobe may be compared in a general way with 

 the hippocampus. 



The caudal portion of the lateral lobe is circumscribed 

 by a diverticle of the ventricle, and becomes completely 

 homologous with the occipito-basal lobe of reptiles. 



Commissures of the Cerebrum. — The exact equivalence of 

 the commissures of the cerebrum is a matter of much diffi- 

 culty in these fishes where the whole dorsal and median por- 

 tion of the tectum cerebri or mantle portion is apparently 

 represented by the pallium cerebri. Considering, however, 

 that the direction in which the cerebrum has been difter- 

 entiated in higher animals is caudad, and that, in the lower 

 brains, bodies which lie caudad or dorsad in higher verte- 

 brates must be sought dorsad or cephalad, it is not difficult to 



