THE FORE-BRAIN OR PROSENCEPHALON 



815 



Sphincter pupillse and Ciliaris muscles. Other fibers have been described as 



I 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 

 ind a pair of lateral walls. 



Optic nerve 

 Crossed fibers 

 Uncrossed fibers 



Optic chiasma 



Optic tract 

 Commissure of Gfudden 



Pulvinar 



Lateral geniculate body 

 Superior colliculus 

 Medial geniculate body 



Nucleus of oculomotor nerve 

 Nucleus of trochlear nerve 

 Nucleus of abducent nerve 





Cortex of occipital lobes 

 FIQ. 722. Scheme showing central connections of the optic nerves and optic tracts. 



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 epithe- 

 lial 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 



