2l8 



THE NERVOUS SYSTEM 



fibers in return. Especially in its ventral subdivision it receives all of the as- 

 cending sensory tracts from the tegmentum of the mesencephalon, as well as 

 fibers from the brachium conjunct! vum and red nucleus. It is much more richly 

 supplied throughout with myelinated fibers than are the other nuclei of the thala- 

 mus. 



The lateral nucleus is subdivided into a dorsal portion, the lateral nucleus 

 proper, and a ventral part, better known as the ventral nucleus of the thalamus. 

 Within the latter are two well-defined nuclear masses. The more medial of 



Tunis umlclrcula 



Corfus gtniatlatitm lattrale 



Gyrus dentalus 



Fig. 157. Frontal section through the human pons, basis pedunculi, thalamus and adjacent 

 structures. Weigert method. (Villiger-Piersol.) 



the two is known as the nucleus centralis (nucleus globosus or centrum media- 

 num) and is surrounded by a well-defined capsule of myelinated fibers (Fig. 157). 

 Ventrolateral to this is the well-defined nucleus arcuatus, which because of its 

 shape is also called the nucleus semilunaris. The pulvinar is a very large mass 

 which forms the most caudal part of the thalamus and is usually considered as 

 a part of the lateral nucleus. 



Function. The medial and anterior thalamic nuclei are closely associated in 

 function and from a phylogenetic point of view represent the older part of the 

 thalamus. They serve as centers for the more primitive thalamic correlations 



