494 THE BRAIN. 



coming 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 rarely in a double row ; the rounded extremity 

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

 According to Kb'liiker 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 outward toward the surface of 

 the convolution divides into numerous fine ramifications. 



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

 by, 1st, the fibres of the posterior peduncles, or restiform bodies, which 

 come from the posterior and lateral parts of the medulla oblongata, to 

 radiate in the white substance of the cerebellum ; and 2d, by those of 

 the anterior peduncles, orprocessus e cerebello ad corpora quadrigemina, 

 which originate from the cerebellum nearer the median line than the 

 termination of the restiform bodies, and thence pass upward and forward, 

 joining the longitudinal tracts of the posterior part of the tuber annulare 

 and crura cerebri. The two lateral halves of the cerebellum are further- 

 more connected with each other by, 3d, the fibres of the middle peduncles, 

 which originate from the white substance on each side, then 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 upon 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 the external gray substance of the cerebellum ; while in its 

 deeper portions both excitability and sensibility become manifest, in 

 proportion as the irritation is applied nearer the medulla oblongata and 

 the commencement of the cerebellar peduncles. Furthermore, its re- 

 moval, either in part or in whole, does not destroy nor essentially 

 diminish either the power of sensation or that of movement. The 

 senses remain active, and the mental faculties are still unchanged, pro- 

 vided the cerebral hemispheres have not been injured. Operations 

 upon this part of the brain are more difficult to perform than those 

 upon the cerebrum, and are much more liable to produce a fatal result. 

 This, however, does not seem to depend upon any direct influence of 

 the cerebellum upon the more vital functions, but is due to its deeper 

 position, the difficulty of exposing it without causing too much hemor- 

 rhage, and especially its proximity to the medulla oblongata. If injury 

 from these causes be avoided, the organ may be extensively wounded 

 or even totally removed without causing death. One-half or two-thirds 

 of it have often been taken away without causing death ; and in one of 

 the experiments of Flourens, a fowl lived for more than four months 

 after its complete extirpation. 



