THE BRAIN 129 



Internal surface : forms lateral wall of 3rd ventricle, and is 

 covered by ependyma. 



Anterior extremity (anterior tubercle) : posterior boundary 

 of foramen of Monro. 



The pineal body is a cone-shaped body placed at the back 

 of the 3rd ventricle, and overlying the superior quadrigeminal 

 bodies. The 3rd ventricle projects backwards into its base or 

 peduncle (pineal recess), which is thus divided into a dorsal 

 part, connecting the pineal body on each side with the optic 

 thalamus, and a ventral part, connecting it with the posterior 

 commissure. 



The posterior perforated spot is a depression containing 

 grey matter placed at the base of the brain, in the angle of 

 divergence of the crura. It is bounded by the corpora albi- 

 cantia in front, and by the pons behind. The anterior part 

 corresponds to the under portion of the floor of the 3rd ven- 

 tricle, and is perforated for bloodvessels to the optic thalami. 



The corpora albicantia are two small whitish bodies, placed 

 in front of the posterior perforated spot and behind the tuber 

 cinereum. They consist of grey matter covered with white 

 fibres, derived from the anterior pillars of the fornix. 



The tuber cinereum is an eminence of grey matter, situated 

 in front of the corpora albicantia, and extending forwards to 

 the optic tract. From its centre a tubular conical process of 

 grey matter, the infundibulum, passes downwards and forwards 

 to the posterior lobe of the pituitary body. 



The pituitary body is a reddish-grey vascular mass lying in 

 the sella turcica. It consists of two lobes, the anterior being 

 the larger. 



The optic commissure or chiasma is the union of the two 

 optic tracts, and is placed in the middle line just in front of 

 the tuber cinereum. From the anterior part the two optic 

 nerves proceed. 



Decussation of the nerve fibres. When the fibres of the tract 

 reach the commissure, they pass across for the most part to 

 form the optic nerve of the opposite side, but a few pass 

 directly into the nerve of the same side. The posterior fibres 

 of the chiasma are described as simply passing between the 

 two inner geniculate bodies. 



The lamina cinerea is a layer of grey matter lying above 

 the optic commissure, and passing from the extremity of the 

 corpus callosum backwards to the tuber cinereum ; laterally 

 it is connected with the grey matter of the anterior perforated 

 spot, which lies under the anterior end of the corpus callosum 

 and is pierced by vessels. 



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