THE TEGMENTUM OF THE CRUS CEREBRI AND ITS GANGLIA. 435 



origin of the crus cerebri proceed from the optic thalamus. 

 The relation of these fasciculi of the crus cerebri and spinal 

 cord which furthermore surround the cerebellar portion of the 

 transverse section of the tegmentum, the red nucleus (fig. 248, 

 Rk in T\ to the radiation of the optic thalamus coming from the 

 retina (fig. 248, iiR) is exactly the same as their relation to the 

 radiations proceeding from the cortex of the cerebrum (fig. 248, 

 R) to the optic thalamus. 



If we suppose the anterior part (fig 245) of the optic thala- 

 mus to be immediately seated upon the commencing crusta of 

 the cerebral peduncle forming the internal capsule, two fan-like 

 sets of fasciculi from the corona radiata are interposed in the 

 inferiorly situated segments between the substance of the optic 

 thalamus and the crusta. The upper of these fans, by the con- 

 vergence of its fasciculi, presents a round area on transverse 

 section, which becomes the central point of organization of 

 each half of the tegmentum of the crus cerebri, and, on account 

 of its containing between its fasciculi a large number of very 

 small nerve corpuscles, swells up into a ganglionic mass, which 

 receives the name of red nucleus of the tegmentum (figs. 246, 

 247, 248, and 249, Rti). This red nucleus is the first intemode 

 of a tract that originates with the above-mentioned fan of the 

 corona radiata in the cortex of the cerebrum, and, on the other 

 hand, stretches to the cortex of the cerebellum. The processus 

 a cerebello ad cerebrum are a free segment of this connecting 

 tract between the two cortical substances. 



The second more slender fan of the corona radiata, which 

 lies beneath the former, is applied to the substance of Soemmer- 

 ing, which sends a pointed process outwards to meet it, the 

 relation of which to the crusta of the cerebral peduncle has 

 already been described. Thus the optic thalamus (fig. 248) 

 rests upon the whole mass of the crus cerebri, of which the 

 crusta at this level already appears in sections as a completely 

 formed structure; the tegmentum, however, so far as regards its 

 spinal-cord portion, being first met with in a completed state 

 in sections made through the region of the corpora quadri- 

 gemina. 



In the corpora quadrigemina there is found a second connec- 

 tion common to them with the optic thalamus and the corpora 



F F 2 



