CHAPTER VIII 



THE HIND-BRAIN 



CONTENTS. 1. Anatomy of hind-brain : afferent and efferent tracts of the three 

 cerebellar peduncles. 2. Preliminary observations on cerebellar functions. 3. Dy- 

 namic phenomena immediately incident on removal of cerebellum. 4. Cerebellar 

 ataxy in dogs and monkeys after removal of half the cerebellum. 5. Cerebellar 

 ataxy after total removal of cerebellum. 6. Cerebellar ataxy. 7. The cerebellum 

 as the centre' of equilibrium ; i 8. And the co-ordinating organ of voluntary 

 movements ; 9. And the organ of subconscious sensations, exercising constant 

 reinforcing action upon the other nerve-centres. 10. Localisation of cerebellar 

 functions. Bibliography. 



IN discussing the medulla oblongata we were obliged to include 

 the pons Varolii, which, both in its structure and its functions, 

 is the continuation of the bulb. Embryclogically, however, while 

 the medulla oblongata arises from the 5th secondary vesicle, the 

 pons and cerebellum originate in the 4th secondary vesicle, and 

 form respectively the ventral and dorsal parts of the Hind-brain 

 or MeTencephalon. 



I. The Hind-brain is more developed in mammals than in other 

 classes of vertebrates. Both the ventral and the dorsal portions 

 present new and special formations which do not exist in lower 

 vertebrates the pons properly so-called, the middle cerebellar 

 peduncles, and the lateral cerebellar lobes. The pons consists 

 of a projecting mass of fibres with an oblique course, which 

 surrounds the ventral surface of the brain - stem, and is 

 collected at the sides into two large bundles that are directed 

 obliquely dorsalwards, and enter the cerebellum as the middle 

 cerebellar peduncles. These are considerably thicker than the 

 restiform bodies or inferior cerebellar peduncles, and the brachia 

 conjunctiva or superior cerebellar peduncles (Figs. 201, 202). In 

 association with this thickening of the middle peduncles the 

 mammalian cerebellum has, besides a median lobe or vermis, 

 lateral lobes or cerebellar hemispheres, which do not exist, or are 

 rudimentary, in the lower vertebrates. This increased develop- 

 ment of the hind-brain in mammals is counterbalanced by a con- 

 siderable relative reduction in the mid-brain, in comparison with 

 that of the lower vertebrates. 



419 



