524 HANDBOOK OF PHYSIOLOGY. 



servations. Some fibres from the tegmentum enter it no doubt, but the 

 main body skirts the ganglion on either side, and does not enter it. 

 Fibres connect the optic thalamus with the superior peduncle of the 

 cerebellum of the opposite side. Fibres connect it with the optic nerves. 

 From the optic thalamus of either side fibres pass to the lenticular 

 nucleus as well as to all parts of the cerebral cortex. 



Lesions of the optic thalamus do not of themselves produce loss of 

 sensation. If such a symptom follows, it is due to pressure upon, or 

 injury to the posterior limb of the internal capsule. The optic thalamus 

 is connected with visual sensations, and may be a reflex-centre for some 

 of the higher reflex actions. 



Of the functions of the external capsule and of the claustrum 

 nothing definite is known. 



The Cerebellum. 



The Cerebellum (7, 8, 9, 10, Fig. 341), is composed of an elongated 

 central or lobe portion, called the vermiform processes, and two hemi- 

 spheres. Each hemisphere is connected with its fellow, not only by 



FiG, 362. Cerebellum in section and fourth ventricle, with the neighboring parts. 1, median 

 groove of fourth ventricle, ending below in the calamus scriptorius, with the longitudinal emi- 

 nences formed by the fasciculi teretes, one on each side; ^, the same groove, at the place where 

 the white streaks of the auditory nerve emerge from it to cross the floor of the ventricle; 3, 

 inferior crus or peduncle of the cerebellum, formed by the restiform body; 4, posterior pyramid; 

 above this is the calamus scriptorius; 5, superior crus of cerebellum, or processus e cerebello ad 

 cerebrum (or ad testes); 6, 6, fillet to the side of the crura cerebri; 7, 7, lateral grooves of the 

 crura cerebri; 8, corpora quadrigemina. (From Sappey after Hirschfeld and Leveille.) 



means of the vermiform processes, but also by a bundle of fibres called 

 the middle crus or peduncle (the latter forming the greater part of the 

 pons Yarolii), while the superior crura with the valve of Vieussens con- 

 nect it with the cerebrum (5, Fig. 361), and the inferior crura (formed 

 by the prolonged restiform bodies) connect it with the medulla oblon- 

 gata (3, Fig. 361). 



