810 



NEUROLOGY 





Structure. The thalamus consists chiefly of gray substance, but its upper sur- 

 face is covered by a layer of white substance, named the stratum zonale, and r;s 

 lateral surface by a similar layer termed the lateral medullary lamina. Its gray 

 substance is incompletely subdivided into three parts anterior, medial, and lateral 

 by a white layer, the medial medullary lamina. The anterior part comprises the 

 anterior tubercle, the medial part lies next the lateral wall of the third ventricle 

 while the lateral and largest part is interposed between the medullary laminae 

 and includes the pulvinar. The lateral part is traversed by numerous fibers which 

 radiate from the thalamus into the internal capsule, and pass through the latter 

 to the cerebral cortex. These three parts are built up of numerous nuclei, the 

 connections of many of which are imperfectly known. 



Thalamus 



Caudate nucleus 



Internal capsule 

 Globus pallidus 

 Putamen 

 Claustrum 

 Insula, 



Corpus callosum 



Lateral ventricle 



Choroid plexus 



Fornix 



Third ventricle 

 Medial medullary lamina 



Intermediate mass 



Third ventricle 



Optic tract 





Amygdaloid nucleus 

 FIG. 718. Coronal section of brain through intermediate mass of third ventricle. 



Connections. The thalamus may be regarded as a large ganglionic mass in which 

 the ascending tracts of the tegmentum and a considerable proportion of the fibers 

 of the optic tract end, and from the cells of which numerous fibers (thalamocortical) 

 take origin, and radiate to almost every part of the cerebral cortex. The lemniscus, 

 together with the other longitudinal strands of the tegmentum, enters its ventral 

 part: the thalamomammillary fasciculus (bundle of Vicq d'Azyr), from the corpus 

 mammillare, enters in its anterior tubercle, while many of the fibers of the optic 

 tract terminate in its posterior end. The thalamus also receives numerous fibers 

 (corticothalamic) from the cells of the cerebral cortex. The fibers that arise from 



