414 



THE PINEAL ORGAN 



posterior commissure, which lie respectively in its superior and inferior 

 peduncles. The body lies in the groove between the superior colliculi 

 of the quadrigeminal plate, and the apex is directed backwards and 

 slightly downwards. The organ receives a partial covering of pia mater, 

 which is derived from the lower layer of the tela choroidea or velum 

 interpositum. The anterior third or half of its upper surface is covered 

 by the layer of ependyma which forms the floor of the dorsal diverticulum 

 or suprapineal recess. This is continuous with the ependyma lining the 



Fig. 278. — Transverse Section of a Brain containing a Tumour of the 



Pineal Organ. 



cavity of the third ventricle, and is reflected anteriorly over the superior 

 commissure and into the pineal recess. The roof of the superior pineal 

 recess is continuous with that of the third ventricle, and has numerous 

 choroidal villi hanging downwards from it and resting on the upper 

 surface of the pineal body. The posterior two-thirds or half of the upper 

 surface is covered by the lower layer of the tela choroidea which is firmly 

 adherent to its capsule. It is in close relation with the great cerebral 

 vein which separates it from the corpus callosum and commissural fibres 

 of the fornix. The splenium projects backwards beyond the apex of the 

 pineal body. The nerve-fibres of the splenium course outward and 



