NERVOUS SYSTEM. VERTEBRATA. 175 



mammals, the hippocampus extends forward as a large 

 arcuate bulging upon the mesial wall of the ventricle ; 

 this proceeds above the cerebral commissures, and reaches 

 a point near the cephalic extremity of the hemisphere. 



[Similar dissections have been made in brains of Erin- 

 aceus (vide infra, D. 230) and Lepus (vide infra, D. 264) in 

 order to demonstrate the difference between the Meta- and 

 Eutheria in regard to this feature.] 



The anterior extremity of this great hippocampal arc is 

 narrower than the more caudal part, and tapers to a 

 rounded extremity. The inferior or caudal extremity is 

 large and plump, and does not taper. In the Monotremes, 

 which are the only other mammals possessing this hippo- 

 campal arc in its undisturbed simplicity, its caudal portion 



CUT SURFACE 

 - OF THE 

 PALLIUM. 



is relatively small, and tapers to a point. In regnrd to 

 these features, the Marsupial approaches much more nearly 

 to the Eutherian plan than does the Monotreme. 



Upon close examination of the ventricular surface of the 

 hippocampus a series of oblique fibres (alveus) may be seen 

 proceeding from the hippocampus to form a fringe-like 

 band at its concave margin. This is thefimbria or forniy, 

 and is here seen in its most simple form. 



Elliot Smith, Journal of Anat. & Phys., vol. xxxii. 

 1897, p. 30. 



D. 211. The two cerebral hemispheres and thev left half of the 

 brain-stem and cerebellum of a Black-faced Kangaroo 

 (Macropits giganteus, var. melanops). 



Above the large elliptical ventral commissure, note the 

 elongated, horizontally-placed, U-shaped dorsal (hippo- 

 campal) commissure, the shape of which is characteristic of 



