LECTURE VI. 



THE CORONA RADIATA, THE CORPUS STRIATUM, THE THALAMUS, AND 



THE SUBTHALAMIC REGION. THE STRUCTURES AT THE 



BASE OF THE BRAIN. 



GENTLEMEN : As you saw in the last lecture, a great part of 

 the coronal fibres terminate in the inter-brain, in the optic thala- 

 mus. The rest pass farther caudad and ventrad in the capsule. 

 Thus they reach the region back of the thalamus and for the 

 most part lie free on the under surface of the brain. This thick 

 bundle of white fibres emerging from the base of the brain is 

 called the foot of the cms cerebri, pes pedunculi, or crusta. 



As you see in the accompanying frontal section, this free 

 portion of the capsule, whose fibres curve backward in the eras 

 cerebri, lies ventrad of the thalamus. Into this, the pes pedun- 

 culi or crusta, pass the fibres of the frontal tract to the pons, 

 of the temporal tract to the pons, and of the pyramidal tract. 

 The coronal optic fibres and the tegmental radiation do not 

 enter the crusta. Farther back under the corpora quadrigemina, 

 just over the crusta, in the same relative position here occupied 

 by the thalamus, lie the fibres which spring from the thalamus 

 and other regions of the brain, and the fibres of the tegmental 

 radiation. At this point the mass of fibres from the fore-, inter-, 

 and mid- brains are divided into a ventral portion (the pes or 

 crusta) and a dorsal portion (the tegmentum). First let us turn 

 our attention to the crusta. The accompanying cut (Fig. 50) is 

 an endeavor to show you the transition of the internal capsule 

 into the pes by a diagrammatic horizontal section. The thalamus 

 is represented as transparent. Posteriorly the section trends 

 sharply downward ; otherwise it would not show the crusta, 

 which is situated at the base of the brain. 



(85) 



