THE DIENCEPHALON. 



II2I 



main hold good for the other nuclei, although the lateral nucleus is particularly- 

 rich in fibres, and therefore of a paler tint, on account of its close relations to the 

 internal capsule and the tegmentum of the cerebral peduncle. 



The mesial nucleus lies between the central gray matter of the ventricular 

 wall and the internal medullary lamina, and is separated by the latter from the lateral 

 nucleus. Its caudal end is bordered internally by the ganglion habenulae, and, behind, 

 by the pulvinar. The anterior nucleus, the smallest of the three, is a wedge-shaped 

 mass, whose rounded base looks forward and corresponds to the anterior tubercle, 

 and whose apex is directed backward and lies between the front ends of the mesial 

 and lateral nuclei, separated from these by the internal medullary lamina, which 

 divides into two diverging levels that embrace the anterior nucleus. In addition to 

 its contribution of radiating fibres which take part in the production of the thalamic 

 radiation, the anterior nucleus contains a compact bundle of fibres traceable into the 

 mammillary body on the base of the brain. These are the constituents of the mam- 

 millo-thalamic tract, or bioidle of Vicq (V Azy7', by which a large part of the fibres 



Fig. 968. 



Fornix 

 Choroid plexii'. 

 I ateral ventricle 



Stratum zonale 

 Caudate inn.lcu'^ 

 Genu of internal capsule 

 Thalamus, mesial nucleus 



Thalamus, lateral 

 nucleus 



Gyrus callosus 



Cingulum 



Corpus callosum 



Striate vein 



Internal capsule 



Putamen 



Caudate nucleus 



Taenia semicircularis 



Internal medullary 

 lamina 



External medul 

 ' lary lamina 



Mammillo- 

 thalamic tract 



Globus pallidus 



Anterior pillars of fornl^./ 



Lamina cinerea 



Anterior commissure 



1,-,-i- Putamen 



i 



""^ Globus pallidus 



' « 1- ■'''S^Thalamo-tegmental 

 '^^ ^"^"^ 



^®**^ Olfactory fibres 



Oblique frontal section through thalamus and anterior commissure ; Weigert-Pal staining. X %• 



Preparation by Professor Spiller. 



coursing within the anterior pillar of the fornix are carried to the thalamus (page 

 1 159). The entire ventral part of the thalamus is occupied by an illy-defined mass 

 of gray matter, known as the ventral nucleus, which lacks sharp definition from 

 the overlying nuclei and in fact is continuous with the lateral nucleus. The ventral 

 nucleus presents a differentiation into the nucleus centralis of Luys, which occupies 

 a mesial position and appears round in section (Fig. 970), and receives fibres from 

 the red nucleus and the posterior commissure, and the nucleus arciformis, which 

 lies ventro-lateral to the preceding nucleus and is crescentic in outline. The ventral 

 nucleus is of importance, not only because it receives the great sensory paths, but also 

 on account of its phylogenetic rank, since, according to Edinger, it, together with the 

 ganglion habenulae, represents the oldest of the thalamic nuclei and is found through- 

 out the vertebrate series. 



Connections of the Thalamus. — Broadly considered, the thalamus may be 

 regarded as a great ganglionic internode interposed in the corticipetal paths around 

 whose cells most of the constituents of the important secondary paths conveying 

 afferent impulses from the spinal cord, the brain-stem and the cerebellum end. 



7f 



