SUBTHALAMIC TEGMENTAL REGION. 



113 



thalamus is cut off from it by another septum of white matter. The anterior 

 separated part is the anterior nucleus of the thalamus or nucleus of the anterior 

 tubercle (a). It contains comparatively large nerve-cells and from its depth a 

 number of fibres pass downwards and converge to form a well-marked bundle 

 (bundle of Vicq-d 1 Azyr\ which, entering the corpus albicans, forms within that 

 tubercle a sharp bend, and appears to pass upwards again in the wall of the 

 ventricle as the anterior pillar of the fornix. There would seem, however, to be no 

 actual continuity between the two (see pp. 129, 130). The middle commissure 

 unites the mesial nuclei across the third ventricle, and is also continuous below 

 on each side with the grey matter of the cavity. It contains nerve-cells and 

 transversely coursing fibres, but many of the fibres are said to loop backwards 

 near the median plane in place of passing across to the opposite side. 



In the trigonum habenulse is a collection of nerve-cells termed by Meynert 

 the ganglion of the habenula. To it, fibres pass from the peduncle of the pineal 

 body, and from it a bundle of fibres (fasciculus retroflexus, Meynerfs bundle (fig. 



Fig. 84. SECTION OF THE INTER-BRAIN NEAR THE JUNCTION WITH THE MID-BRAIN, SHOWING THE 

 SUBTHALAMIC TEGMENTAL REGION. Magnified about 2 diameters. From a photograph (E. A. S. ). 



The section passes nearly horizontally, so as to cut the fibres of the internal capsule across transversely. 

 It is just above and in front of the corpora mamillaria. 



(., tasnia (attachment of epithelial roof of ventricle) ; r. ///. , ventriculus tertius ; sir., stria pinealis ; 

 Th., thalamus; n.t., mesial nucleus of thalamus; opt., optic fibres passing to pulvinar ; z.i., zona 

 incerta ; c.s., corpus subthalamicum ; c.i., capsula interna ; a. I., ansa lenticularis ; /., anterior pillar 

 of fornix passing backwards towards corpus albicans; V.A., bundle of Vicq d'Azyr, passing upwards 

 and forwards from corpus albicans into thalamus ; x. , white bundle containing a central nucleus of 

 grey matter ( ? the fasciculus retroflexus of Meynert) ; g, g', special groups of nerve-cells, of which ij 

 is the hinder end of the ganglion habenulse. 



84, x) ) passes with a curved course through the tegmentum on the mesial side of 

 the red nucleus towards the place where the cerebral peduncles diverge ; where, 



