THE THIRD VENTRICLE AND INTER-BRAIN. 127 



inferior horn. It covers the cushion-like projection (the pulvi- 

 nar) of the thalamus, which forms a small part of both roof and 

 inner wall. Behind, it is attached to the cms of the fornix, from 

 which it extends forward to the stria terminalis. The epithelium 

 covers the chorioidal -fissure except at the lower part, where there 

 is a small cleft which forms a communication between the horn 

 and the anterior subarachnoid space. Through the chorioidal 

 fissure a fold of pia mater projects toward the ventricle, and 

 pushing the epithelium before it into the horn, forms the chorioid 

 plexus (Figs. 35 and 36). Bounding this part of the chorioidal 

 fissure below and behind, there is a serrated free border of cortex 

 called the dentate fascia. The dentate fascia (Figs. 38, 42 and 62) 

 folds medially in front of the hippocampal fissure and with the 

 hippocampus, the gyrus hippocampi and the eminentia collateralis 

 forms an S-shaped fold of the cortex. The S-shape is perfect 

 in the left hemisphere, when the anterior segment of a coronal 

 section is viewed from behind. The top of the letter is the dentate 

 fascia; the superior curve is the hippocampus, produced by the 

 hippocampal fissure; the lower convexity is the gyrus hippo- 

 campi; the lower concavity, open toward the ventricle, is 

 the groove between the hippocampus and the eminentia col- 

 lateralis. 



THE THIRD VENTRICLE AND INTER-BRAIN. 



(Ventriculus Tertius and Diencephalon.} 



The inter-brain (diencephalon) is median in position (Figs. 

 27, 28, 29, 30 and 40). It is situated beneath the fornix and the 

 layer of epithelium extending from the border of the fornix to the 

 stria terminalis. The chorioid tela of the third ventricle only 

 intervenes between them. Laterally, it is bounded by the superior 

 laminae of the internal capsules. The ventricle of the inter-brain 

 is the third in number. The third ventricle, therefore, is located 

 in the median plane; and is at a lower level than the ventricles 

 of the hemispheres. Through the interventricular foramina, 

 its anterior part (the aula) communicates with each lateral ventri- 

 cle, and the cerebral aqueduct connects it, behind, with the fourth 

 ventricle (Figs. 17 and 41). The third ventricle is fissure-like. 



