100 Anatomy of the Nervous System 



The postcommissural hippocampus, i.e., the portion behind 

 and below the corpus callosum, is large and well-developed 

 (Fig. 8, Pis. IV., XV.-XX.). 



The hippocampal formation is divided into two parts, the 

 hippocapipiis proper and the fascia dentata or gyrus dentatus 



Fig. 6 



Diagram of the medial surface of the cerebral hemisphere of the 

 frog, with the primordium hippocampi shaded. From a sketch by Herrick 

 made with sHght modification from a model by Johnston. 



(Pis. IV., XV.-XX.), The hippocampus proper is the larger 

 part, which is folded in at the hippocampal fissure and forms 

 a prominent ridge in the ventricle. The ventricular surface 

 is covered with a layer of white fibres, the alveus, composed 

 of hippocampal projection fibres, and these join a large tract 



Fig. 7 



Diagram of the medial surface of the cerebral hemisphere of a 

 marsupial (opossum), from Johnston; hippocampus solid black; septum 

 shaded, with pallial and basal regions distinguished (see p. 93). 



