468 



PEOF. Q. ELLIOT SMITH ON THE MOEPHOLOGY OF THE 



the little recess will be fovind to be walled on each side by the whole mass of the para- 

 terminal body, a large part of which (05) intervenes between the recessus superior and 

 the ventral margin of the hippocampal formation. [I nse the term " hippocampal 

 formation" here in preference to "fascia dentata," because the latter body is obviously 

 in the process of formation as a specialization of the lower extremity of the hippo- 

 campus.] 



At the dorso-mesial angle of the hemisphere the neopallium will be found in a state of 

 transition. The scattered nerve-cells are becoming collected into a compact column, 

 which is readily recognized ixpon the mesial wall (after comparison with the adult brain) 

 as the layer of pyramidal cells of the hippocampus. This layer of cells is already under- 

 going a lateral bending, but it is a significant fact that only the very slightest furrow 



Fig. 10. 



CM 



Scheme drawn from a coronal section through the brain of a young ErJiidnu, which had been 



stained with lithium carmine. 



has yet made its appearance upon the mesial wall (o). It is hence clear (as Hochstetter 

 has shown) that the supposed furrow called " Bogenfurchc " by Schmidt and " Ammons- 

 furclie " by Mihalkovics, which makes its appearance at a much earlier stage of 

 development, cannot have anything to do with the true hippocampal fissure, which at 

 this late stage is only just beginning to appear. In fact the slight furrow c, Avliich is the 

 first representative of the hippocampal fissure, is really due to the peculiar inrolling of 

 the hippocampal formation which takes place pari passu with the develojjment of the 

 fascia dentata. The latter arises (see fig. 16) as a rapid proliferation of the ventral 

 extremity of the column of cells which elsew'here develops into the layer of pyramidal 

 cells. As these cells increase in number at a rapid rate, the surface area corresponding 

 to them grows much more rapidly than the deeper regions, and becomes bent up into 

 the peculiar pouch-like shape which the fully developed fascia dentata always presents 

 in transverse section in the adult brain. This rapid growth in superficial extent seems 



