2l8 THE CEREBRUM. 



The nucleus hypothalamicus (Luysi) (Figs. 30 and 42) is a 

 pigmented bi-convex mass of gray matter placed ventro-lateral 

 to the red nucleus, and between it and the basis pedunculi. It 

 is separated from the red nucleus by the zona incerta. It con- 

 stitutes an important relay for certain corticipetal fibers of the 

 tegmentum and gives origin to others belonging to the cortical 

 fillet. Certain descending fibers from the striate body terminate 

 in this nucleus. The latter run through the tuber cinereum, 

 just above the posterior border of the optic chiasma, and form 

 the commissura superior (Meynerti), Gudden's commissure being 

 called the commissura inferior. 



Metathalamus. The metathalamus is made up of two ganglia 

 at the posterior end of the thalamus, called the geniculate bodies 

 (Fig. 65). The lateral geniculate body (corpus geniculatum 

 laterale] contains pigmented multipolar cells, which receive 80 

 per cent, of the optic fibers in the corresponding tract and give 

 origin to a like per cent, of the corticipetal fibers in the occipito- 

 thalamic radiation; and, also, receive corticifugal fibers from the 

 same radiation and originate a part of the brachium superius. 

 The latter are reflex in function. As the dark cell-bodies are 

 arranged in layers separated by laminae of fibers, the body has a 

 stratified appearance. The medial geniculate body (corpus 

 geniculatum mediate) is gray in color. Placed at the end of the 

 medial root of the optic tract, it would at first appear to be con- 

 cerned in vision; but it is not visual in function. Moreover, it is 

 a very important station in the auditory path. The medial optic 

 root is merely Gudden's commissure, the fibers of which are 

 supposed to rise in the medial geniculate body. This body 

 contains chiefly fusiform cell-bodies which, in addition to their 

 connection with the inferior commissure (of Gudden), receive 

 the end-tufts of fibers in the brachium inferius and send their 

 axones through the acustic, or temporo-thalamic radiation to the 

 auditory cortex; the cells also receive corticifugal fibers through 

 the temporo-thalamic radiation and, probably, shoot some of 

 their axones backward through the brachium inferius to the 

 corpora quadrigemina. The latter are reflex in function. 



Ablation of the lateral geniculate body interrupts the visual 



