74 ESSENTIALS OF PHYSIOLOGY. 



but themselves arise in cell-stations in the medulla oblongata. It also 

 receives afferent paths from the cerebral hemispheres, but whereas 

 the connection with the cerebral hemispheres is a crossed one, that 

 with the spinal cord is for the most part uncrossed. 



The efferent fibres from the cerebellum are (1) those which run in 

 the superior peduncles (brachia conjunctiva) to the mid-brain and 

 thalamus, (2) fibres in the middle peduncles to the nuclei pontis, and 

 (3) those which run in the restiform bodies to the vestibular nuclei and 

 the medulla oblongata. 



THE FUNCTIONS OF THE CEREBELLUM. 



A knowledge of the cerebellar functions has been obtained partly by 

 observation of the results of disease in man and partly by experiments 

 on animals. When the normal impulses from the cerebellum are want- 

 ing, there is defective co-ordination of muscular movements as well 

 as defectrjre^ muscle tone. As a result, the power of maintaining the 

 equilibrium of the body is impaired and the gait is staggering, though 

 consciousness and volition are not affected. Further, observation of 

 the results of localised lesions shows that different areas of the cerebellar 

 cortex are associated with different groups of muscles, although no 

 histological difference can be detected in the various parts of the 

 cerebellar cortex. The cerebellum is, therefore, a reflex_centre for the 

 maintenance of muscle. tone and for the co-ordination of muscular 

 movemgnls. It is especially concerned with the maintenance of the 

 position of the body in relation to gravity, and with co-ordination of 

 the movements of the body as a whole. 



The effects of removal of the cerebellum, or of any part of it, vary 

 according to the length of time that has elapsed since the operation was 

 performed. The immediate effect of complete removal is chiefly a con- 

 dition of jitaxja or inco-ordination. If a pigeon, for example, shortly 

 after removal of its cerebellum, attempts to fly, it only succeeds in 

 making exaggerated and inco-ordinated movements of its wings. The 

 attempts of a dog to walk under the same circumstances are equally 

 futile. After some weeks or months, the animal regains the power of 

 co-ordinated movement to a certain degree. The pigeon is able to fly 

 and the dog to walk, but the power of movement is still greatly 

 impaired. The condition is described as one of asthenia, atonia, and 

 astasia, that is, there is loss of strength, loss of muscle tone, and un- 

 steadiness of movement due to a condition of tremor accompanying 

 attempts at muscular contraction. A dog is no longer able to walk 

 with the normal diagonal movements of the limbs, but progresses by 

 means of a series of jumps. The explanation of the partial recovery 



