448 THE BRAIN 



The most projecting part is called the pulvinar. But the 

 posterior end of the thalamus shows another prominence, 

 which is situated below and to the lateral side of the pulvinar. 

 It is oval in form, and receives the name of the corpus 

 geniculatum laterale. 



The anterior two-thirds of the medial surfaces of the two 

 thalami are placed very close together, and are covered not 

 only with the lining ependyma of the third ventricle, but also 

 with a moderately thick layer of grey matter continuous with 

 the grey matter which surrounds the aquaeductus cerebri 

 (Sylvius). A band of grey matter, termed the massa intermedia, 

 crosses the third ventricle and joins the two thalami together. 



Corpus Pineale. The pineal body is a small body of a 

 darkish colour, and about the size of a cherry-stone, which is 

 placed on the dorsal aspect of the mesencephalon between 

 the posterior extremities of the two thalami (Figs. 176, 179). 

 It occupies the depression between the two superior colliculi of 

 the quadrigeminal lamina, and is shaped like a fir-cone. Its 

 base, which is directed forwards, is attached by means of a 

 hollow stalk or peduncle. The stalk is separated into a 

 dorsal and a ventral part by a continuation into it of a pointed 

 recess of the cavity of the third ventricle. The dorsal part 

 of the stalk becomes continuous, on each thalamus, with the 

 tsenia thalami, and through it pass the fibres of the habenular 

 commissure ; the ventral part is folded round a narrow but 

 conspicuous cord-like band of white fibres (posterior commissure} 

 which crosses the median plane immediately below the base of 

 the pineal body. 



Commissura Anterior Cerebri. In the anterior part of the 

 cleft between the two thalami, and immediately anterior to 

 the columns of the fornix, a round bundle of white fibres 

 will be seen crossing the median plane (Figs. 177, 173). It 

 is the anterior commissure. It is very much larger than the 

 posterior commissure, and will be afterwards followed towards 

 the temporal lobe, in which the greater part of it ends. 



Ventriculus Tertius. The third ventricle is the name 

 given to the deep, narrow cleft between the two thalami. It 

 is deeper anteriorly than posteriorly, and extends from the 

 pineal body posteriorly to the anterior commissure and lamina 

 terminalis anteriorly. Its floor is formed by the parts already 

 studied within the interpeduncular fossa on the base of the 

 brain, viz., the tuber cinereum, the corpora mamillaria, and 



