502 THE BRAIN 



venes between the thalamus and the caudate nucleus and 

 contains the vena terminalis and the stria terminalis. On 

 the medial side, the superior surface of the thalamus is 

 separated, in its anterior half, from the medial surface by a 

 sharp edge, or prominent ledge, of the ependyma of the 

 third ventricle. This is called the tcenia thalami, and the 

 ridge which it forms is accentuated by the fact that subjacent 

 to it there lies a longitudinal strand of fibres called the stria 

 medullaris. A short distance anterior to the pineal body the 

 tsenia lies upon the upper border of a raised white band, the 

 habenula. 



The habenula divides posteriorly into two parts, one of which becomes 

 continuous with the pineal body, whilst the other passes across to the 

 opposite habenula, through the habenular commissure^ which lies anterior 

 to the pineal stalk. 



Between the habenula medially and the upper quadrigeminal 

 body posteriorly, lies a small triangular depressed area, the 

 trigonum habenulcz. 



The ^superior surface of the thalamus is slightly convex, 

 and is of a whitish colour owing to the presence of a thin 

 superficial coating of nerve fibres (stratum zonale). It is 

 divided into two areas by a faint oblique groove which 

 begins near the anterior extremity of the thalamus, and ex- 

 tends obliquely, laterally and posteriorly. This sulcus corre- 

 sponds to the free lateral edge of the fornix. The two areas 

 thus mapped out are very differently related to the ventricles 

 of the brain. The lateral area includes the anterior extremity 

 of the thalamus, and forms a part of the floor of the lateral 

 ventricle ; it is covered with ependyma, and overlapped by 

 the chorioid plexus. The medial area intervenes between 

 the lateral and third ventricles of the brain, and takes no 

 part in the formation of the walls of either. It is covered 

 with the tela chorioidea, above which is the fornix. It 

 includes the posterior extremity of the thalamus. 



The anterior extremity of the thalamus, called the anterior 

 tubercle, is rounded and prominent. It projects into the 

 lateral ventricle, lies postero-lateral to the free portion of the 

 column of the fornix, and bounds the interventricular foramen 

 posteriorly. 



The posterior extremity of the thalamus is very prominent, 

 and projects posteriorly over the mesencephalon (Fig. 206). 

 This projecting part is called the pulvinar. But the posterior 



