|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|Sphincter pupillæ and Ciliaris muscles. Other fibers have been described as reaching the cerebellum through the superior peduncle; while others, again, are lost in the pons.|
The Third Ventricle (ventriculus tertius) (Figs. 716, 720).The third ventricle is a median cleft between the two thalami. Behind, it communicates with the fourth ventricle through the cerebral aqueduct, and in front with the lateral ventricles through the interventricular foramen. Somewhat triangular in shape, with the apex directed backward, it has a roof, a floor, an anterior and a posterior boundary and a pair of lateral walls.
FIG. 722 Scheme showing central connections of the optic nerves and optic tracts. (See enlarged image)
| The roof (Fig. 723) is formed by a layer of epithelium, which stretches between the upper edges of the lateral walls of the cavity and is continuous with the epithelial lining of the ventricle. It is covered by and adherent to a fold of pia mater, named the tela chorioidea of the third ventricle, from the under surface of which a pair of vascular fringed processes, the choroid plexuses of the third ventricle, project downward, one on either side of the middle line, and invaginate the epithelial roof into the ventricular cavity.|
| The floor slopes downward and forward and is formed mainly by the structures which constitute the hypothalamus: from before backward these are: the optic