THE CEREBELLUM. 497 



lum remained in nearly the same condition as immediately after the 

 operation; about two-thirds of its substance being deficient, with no 

 regeneration of the lost parts. The accompanying figures show the 

 appearances in this brain as compared with that of a healthy pigeon. 



Fig. 164. Fig. 165. 



BRAIN OP HEALTHY PIGEON Pro- BRAIN OP OPERATED PIGEON 



file view. 1. Cerebral hemisphere. 2. Optic Profile view showing the mutilation of 



tubercle. 3. Cerebellum. 4. Optic nerve. the cerebellum. 

 5. Medulla oblongata. 



Fig. 166. Fig. 167. 



BRAIN OP HEALTHY PIGEON Pos- BRAIN OP OPERATED PIGEON 



terior view. Posterior view showing the mutilation 



of the cerebellum. 



In the three remaining cases the quantity of nervous substance 

 removed amounted to about one-half the mass of the cerebellum. The 

 loss of co-ordinating power, immediately after the operation, though 

 less complete than in the preceding instance, was perfectly well marked ; 

 and in little more than a fortnight the animals had nearly or quite 

 recovered the natural control of their motions, so far as could be seen 

 while they were kept under observation. 



It is evident that in these cases, if the cerebellum be really the seat 

 of a physiological co-ordinating power, there are two effects produced 

 by the operation, which should be carefully distinguished from each 

 other. The first of these effects is the shock due to the sudden injury 

 of the cerebellum as a whole. This effect is temporary, and may be 

 recovered from in time, provided the animal be sufficiently strong to 

 survive the immediate mechanical lesion. The remaining effect is that 

 due to the loss of nervous substance ; and this effect must of course be 

 permanent, unless the nervous matter be regenerated. In the cases 

 detailed above, the greatest amount of disturbance seems to have 

 depended upon the sudden injury to the nervous centre as a whole ; and 

 the animals recovered, to a great extent, their power of co-ordination, 

 notwithstanding that from one-half to two-thirds of the substance of 

 the cerebellum was permanently lost. 



