84 Anatomy of the Nervous System 



intermediate mass or soft commissure {massa intermedia, corn- 

 mi ssura mollis, commissura media thalami) (Pis. XVIII.-XX.). 



In the rat and other lower mammals the central gray 

 matter is more largely developed than in man, containing a 

 number of distinct nuclei and having the area of fusion in 

 the intermediate mass extended so as to obliterate a large 

 part of the third ventricle. The chief median mass of cells 

 is given the name of nucleus reuniens {nucleus rhomboidalis) 

 (Pis. XIX., XX.), though Winkler and Potter confine this 

 term to one of the cell-groups which can be distinguished in it. 



Lateral and ventral to the foregoing portions of the 

 thalamus, we observe an extensive region which is a more 

 recent acquisition, from the phylogenetic standpoint. This 

 is the ventro-lateral group of nuclei, which is related in 

 development to the cerebral cortex, its general function 

 being that of an antechamber to the latter, particularly for 

 general somatic sensory impulses. It is divisible into two 

 main parts, ventral and lateral, in each of which a number 

 of nuclei are to be found. The term lateral nucleus is fre- 

 quently used to include both parts, i.e., the whole ventro- 

 lateral group, but will not be employed in that sense here. 



In the human brain, the ventral nucleus {nucleus ventralis 

 thalami) contains, besides other gray matter, two centres 

 which are very clearly defined in Weigert sections. These 

 are a rather large, round mass, the nucleus centralis or medial 

 centre of Luys {centrum medianum, 7iucleus glohosus thaliami),^ 

 and a curved body just ventral to this, the nucleus arcuatus 

 or nucleus semilunaris {corpus patellare). These, however, 

 do not stand out in the same distinct way in the brains of 

 lower mammals, and the homologies seem not to be certain 

 in many cases. Like the anterior and medial group, the 

 ventral nucleus is not most highly developed in the highest 

 mammals, and it is quite large in the rat (Pis. XVHI.-XX.) 



The ventral nucleus receives most of the terminals of the 



^This is included by Kappers in the medial nucleus. 



