THE CEREBRUM 



437 



posing it is continuous with the thin white layer (alveus) which 

 is spread over the surface of the hippocampus. The fimbria 

 has two free surfaces superior and inferior \ a sharp, free medial 

 border, which lies immediately above the fascia dentata, and 

 below the chorioidal fissure ; and a lateral border, attached to 

 the hippocampus at its junction with the fascia dentata. It 

 consists of the white fibres of the alveus, which assume a 

 longitudinal direction at the margin of union of the hippo- 

 campus and the fascia dentata, and ascend to become the 



Pes hippocampi 

 Hippocampus 

 Anterior collateral eminence 



Trigonum collaterale \ 

 Calcar avis 



Posterior horn 

 Bulb of cornu 



FIG. 171. Dissection to show the Posterior and Inferior Cornua of the 

 "Lateral Ventricle. 



corresponding crus of the fornix (see p. 442). It lies between 

 the chorioid fissure and the fascia dentata (Fig. 171). 

 Anteriorly, it runs into the recurved extremity of the uncus ; 

 and postero- superiorly, as already stated, it becomes con- 

 tinuous with crus of the fornix. 



Chorioid Fissure of the Cerebrum. When the pia mater 

 in the region of the hippocampal gyrus and the fascia dentata 

 is removed from the surface of the brain, the chorioid plexus 

 in the interior of the inferior horn of the lateral ventricle is some- 

 times withdrawn with it, and a fissure then appears between the 

 fimbria and the roof of the ventricular horn. That fissure is 

 III 28 a 



