176 Journal of Comparative Neurology, 



explanation of plate xxvi. 



Fig. I. Dorsal view of the brain of Philohela minor, x 2. 



Fig. 2. Ventral view of the same. 



Fig. J. Lateral view of the same. 



Fig. 4. Dorsal view of the brain of Hydrochelidon nigra, X 2. 



Fig. 5. Lateral view of the brain of Aquila chryssetos. Natural size. 



Fig. 6. Dorsal view of the same- 



Fig. 7. Dorsal view of the brain of Pelicanus erythorhynchos. Natural 

 size. 



VII. The Callosum and Hippocampal Region in Marsupial 

 AND Lower Brains, with Plates IX and XXVII. 



By C. L. Herrick. 

 In view of the fact that Dr. Ale.xander Hill, in his recent 

 monograph "On the Cerebrum of Ornithorhynchus paradoxus" 

 finds "it quite impossible to gather Professor Herrick's views 

 with regard to the dorsal commissure in DidelpJiys,'' it seems 

 necessary to further define them. After expressing agreement 

 with the position of Osborn, the passage in question runs as fol- 

 lows : ' ' The motor cortex as such is thrown well cephalad, 

 and the fornicate gyrus is carried forward along the mesial sur- 

 face, as may be seen from an inspection of the transverse sec- 

 tions of Plate A. [This Journal, Feb., 1892.] Thus it hap- 

 pens that the caudal portion of the dorsal commissural system 

 is much more highly developed than the cephalic or callosal 

 portion. The latter consists of a few fibres which spring from 

 the anterior prolongation of the sphenoid fissure, if this term 

 may be applied to the fissure which bounds the cephalad con- 

 tinuation of the fornicate gyrus." Although minute discussion 

 of these parts was (and must still remain) reserved for a more 

 opportune time it seems that the morphological conception then 

 held was clearly stated. The belief that the two commissures 

 known as the callosum and hippocampal or fornix commissures 

 are essentially homodynamous and are similarly related to the 

 cephalic and caudal regions respectively is not a new or morpho- 

 logically startling idea. Any one who has followed the devel- 

 opment of the two commissures in the embryo of say the mouse 

 or cat will find it hard to appreciate the difficulties which beset 

 the conception for those who are familiar only with the condi- 



