THE BRAIN. 435 



anaesthesia which results. Hemianaesthesia of cerebral origin, accord- 

 ing to the same observer, is characterized by the fact that, together 

 with loss of sensibility in the body and limbs, there is a similar insensi- 

 bility in the integument of the head and face, and in addition a loss or 

 impairment of the special senses ; taste, smell, hearing, and vision being 

 all more or less affected, on the side opposite to that of the cerebral 

 lesion. This will serve to distinguish hemianaesthesia due to injury 

 of the brain from that caused by a lesion of the spinal cord, in which 

 the only symptom present is loss of sensibility on one side of the body. 



The Cerebellum. 



The cerebellum, though much inferior in size to the cerebrum, con- 

 sists, like it, of a folded cortical gray layer surrounding a central mass 

 of white substance. The cortical layer is only about one-half as thick 

 as that of the cerebrum ; being nowhere over 1.5 millimetre in thickness. 

 But its convolutions are very compactly arranged in the form of thin, 

 closely adjacent laminae ; so that it contains a comparatively large 

 quantity of gray substance. 



The cortical layer of the cerebellar convolutions is penetrated by 

 fibres from the interior white substance, and contains nerve cells 

 of various form and size. The most characteristic are flask-shaped 

 cells, arranged in a single or double row ; the rounded extremity 

 of each cell being directed inward, the pointed extremity outward. 

 According to Kolliker and Henle, the cells usually give off prolonga- 

 tions in two opposite directions ; that which passes inward toward the 

 white substance being unbranched and resembling the axis-cylinder of 

 a nerve fibre, while that which passes toward the surface of the con- 

 volution divides into numerous ramifications. 



The cerebellum is connected with the rest of the cerebro-spinal axis, 

 1st, by the inferior peduncles, or restiform bodies, which come from 

 the posterior and lateral parts of the medulla oblongata, to radiate in 

 its white substance ; and 2d, by the superior peduncles, or processus e 

 cerebello ad corpora quadrigemina, which originate from the cerebel- 

 lum nearer the median line than the restiform bodies, and thence pass 

 upward and forward, joining the longitudinal tracts of the tuber annu- 

 lare and crura cerebri. 3d, The two lateral halves of the cerebellum 

 are furthermore connected with each other by the middle peduncles, 

 which originate from the white substance on each side, and pass forward 

 and downward to meet in front upon the under surface of the tuber 

 annulare, forming the arched commissure of the pons Varolii. 



Physiological Properties of the Cerebellum. The general result of 

 experimental operations on the cerebellum shows that the surface of 

 this organ is inexcitable by ordinary means, and that its mechanical 

 irritation gives no evidence of sensibility. Flourens, Longet, Yulpian, 

 and experimenters in general, have recognized the fact that neither 

 sensation nor muscular contractions are produced by touching or 

 wounding its external gray substance ; while in its deeper portions 



