124 THE CEREBRUM. 



Eminentia collateralis (trigonum collaterale), 



Hippocampus, 



Crus of fornix. 

 Inner wall (medial) 



Epithelium (of hemisphere wall) covering 



Pulvinar, 



Chorioid plexus, 



Chorioidal fissure, and 



Dentate fascia. 



The structures in the roof of the inferior horn have been suffi- 

 ciently described. They are easily understood when it is recalled 

 that the roof of the horn is continuous with the outer wall and 

 floor of the central part of the ventricle; the tapetum, the internal 

 capsule (inferior lamina), the cauda, amygdala and the stria 

 terminalis form it. 



Beginning at the trigonum collaterale (Figs. 38 and 39) and 

 extending along the outer border of the floor to the end of the 

 inferior horn there is sometimes a low ridge caused by the collateral 

 fissure. It is the eminentia collateralis, and is present only when 

 the anterior part of the collateral fissure, as well as the middle 

 part, is a complete fissure. The short eminence at the entrance 

 to the inferior horn, called the trigonum collaterale, is constant 

 in its presence; it is produced by the middle division of the col- 

 lateral fissure. In front of this eminence and internal to it is a 

 prominent ridge, the hippocampus, which enlarges downward to 

 a lobulated extremity, called the digitations (digitationes hippo- 

 campi, Fig. 39). The ridge is due to the infolding of the floor 

 over the hippocampal fissure on the medial surface of the cere- 

 brum. The ventricular surface of the hippocampus is formed 

 by a lamina of white matter, the alveus, but the deeper part is 

 cortical matter composed almost entirely of pyramidal cell-bodies. 

 The cms o] the fornix (fimbria hippocampi) rests in the concavity 

 of the hippocampus, where most of its fibers originate, though 

 a small bundle of them passes beyond it to its origin in the uncus. 

 The chorioid epithelium (lamina chorioidea epithelialis) (Figs. 

 118, 62 and 35), -representing the hemisphere wall, forms the 

 floor of the chorioidal fissure and the whole medial wall of the 



