618 Dynamic Theory. 



has been sufficient!}' described. Its connections with the medulla ob- 

 longata and the spinal cord are especially intimate, and its functions 

 must therefore be considered as having been developed in relation to 

 the functions of those parts. It has no direct connection with the cere- 

 brum, and the natural inference would be that although it may be sub- 

 ject to a special influence from that organ, and no doubt it is, neverthe- 

 less it is a complete machine of itself, operated by a set of stimulations 

 from the sense organs through the medulla oblongata, which are compe- 

 tent to set up action in it entirely independent of the cerebrum. 



Throughout the vertebrate sub-kingdom we find the development of 

 the cerebellum to correspond with the degree and energy of muscular 

 co-ordination possessed by the animal. Among the fishes, reptiles and 

 birds, this organ is relatively large in those having the most diversified 

 and complicated modes of muscular action, as shown in chap. 58. The 

 same is shown in the mammals, the cerebellum increasing in relation to 

 the spinal cord, in the proportion in which the muscular co-ordinations 

 and activities increase. The cerebellum of birds is larger than that of 

 the lower mammals. But in those mammals in which the activities in- 

 volve complicated and co-ordinated movements of the several muscles, 

 the cerebellum is of corresponding -size. The differentiation of the 

 limbs from mere organs of terrestrial or aquatic locomotion, to organs 

 adapted to digging, climbing, 'flying or grasping, involve an increase in 

 the condensing and distributing power of the cerebellum. All such dif- 

 ferentiations of limbs involve the fore limbs to a much greater degree 

 than the hind ones. The latter are generally reserved ( in the land ani- 

 mals ) for terrestrial locomotion chiefly. But as the fore limbs are grad- 

 ually developed into greater dexterity, they resign to the hind limbs the 

 task of locomotion, which involves the maintenance of an upright posi- 

 tion on those limbs, and calls into use a greater variety of muscles, and 

 requires a more delicate balancing and constant tension of those mus- 

 cles. Thus compare the turkey with the lizzard, figs. 298, 296. The 

 cerebellum of the latter is hardly as large as the optic lobes, while that 

 of the former is not only very much larger, but is greatly increased in 

 effectiveness by its numerous transverse convolutions. The chief su- 

 periority of the brain of the bird over that of the reptile, is in the cere- 

 bellum. The cerebellum of the bear is likewise superior relatively to 

 that of the dog, and the former is correspondingly much more handy 

 with his fore paws in climbing and grasping, and much better able to 

 use his hind legs in standing and walking in an upright position. 



In the man-like apes, there is a great advance in the cerebellum over 

 that of the inferior mammals. And in their activity, the variety of 

 their movements, and their ability to sit or stand on their lower extrem- 

 ities while using their fore limbs as hands and arms ? they are far su- 



