THE RHINENCEPHALON 



279 



defined zone, the stratum lucidum. Their apical dendrites are directed toward 

 the molecular layer and form the chief constituent of the stratum radiatum. 

 The axons of these cells, after giving off collaterals, enter the alveus. 



The layer of polymorphic cells, also known as the stratum oriens, contains 

 cells of Martinotti, that send their axons into the molecular layer, and still other 

 cells the axons of which enter the alveus. 



The alveus is a thin white stratum which separates the preceding layer from 

 the ventricle. It is continuous, on the one hand, with the white center of the 



Alveus 

 Layer of polymorphic cells 



Layer of pyramidal 

 cells 



Stratum lucidum\ 

 Stratum radia- 

 tum 



. Molecular layer 

 I Stratum lacunosum 

 Tangential fibers 



Lateral ventricle 



Fimbria 



Hippocampus / 



Fascia dentata 



Molecular layer 

 Granule layer 

 Layer of polymorphic cells 



Subictilum 



Fig. 210. Diagram of the structure and connections of the hippocampus. The arrows 

 show the direction of conduction: A, molecular layer, and B, pyramidal cell layer of the subic- 

 ulum; F, hippocampal fissure. (Cajal.) 



hippocampal gyrus, and on the other with the fimbria. Through it the efferent 

 fibers of the hippocampus enter the fimbria and fornix. The fibers of the hippo- 

 campal commissure are also carried in the fimbria and enter the hippocampus 

 through the alveus. 



The fascia dentata also belongs to the archipallium and is closely related to 

 the hippocampus, which it resembles somewhat in the structure of its three 

 strata: the molecular layer, granule layer, and layer of polymorphic cells (Fig. 

 210). The granules may be regarded as modified pyramidal cells of small size, 

 ovoid or fusiform in shape. Each possesses instead of a single apical dendrite 

 'two or three branching processes which extend into the molecular layer. The 



