132 PROFESSOR DAVID HEPBURN ON 



IV. THE HIND BRAIN. 



(a) The Cerebellum. As is usual among carnivores, the cerebellum possessed a 

 relatively large vermis in proportion to the size of the hemispheres. When examined 

 in longitudinal section (fig. 2), the relation of the vermis to the 4th ventricle and the 

 other constituents of the hind brain presented a great similarity to the corresponding 

 appearances seen in the human brain.* 



The central lobe rested upon the superior medullary velum and possessed a lingula. 

 The culmen and declive were similarly recognisable, as were also the nodule and the 

 tonsil upon the inferior or ventricular aspect of the vermis. The pyramid, the tuber 

 valvidse, and the folium cacuminis were not so easily determined in the brain of the seal 

 as they are in the brain of man, because, whereas in the latter these structures are turned 

 towards the floor of the skull, in the former they were turned more towards the hinder 

 end of the vermis. 



The hemispheres were small and practically impossible of the detailed subdivision 

 which is customary in the descriptions of the human cerebellum, and any attempt to do 

 so would introduce unnecessary risks of error. In a measure, the points of entrance of 

 the middle cerebellar peduncles from the pons Varolii provided a guide to what might 

 be regarded as the dorsal and ventral portions of the cerebellum. On this assumption, 

 the biventral lobe and the tonsil projected laterally some distance beyond any other part 

 of the hemisphere, while the flocculus formed a mass of considerable size which over- 

 lapped the middle peduncle from behind. If we accept the position of the middle 

 cerebellar peduncle as a sufficiently reliable guide from which to continue the great 

 horizontal fissure by means of which the upper and lower aspects of the human 

 hemisphere are located, then in the brain of this seal all that remained of each hemi- 

 sphere, in addition to the objects already mentioned, occupied the same aspect and was 

 directed towards the tantorium. Nevertheless, it was divided into two clearly defined 

 areas by a fissure which commenced at the point where the middle peduncle entered 

 from the pons Varolii. If, now, we name these lobes respectively superior -anterior and 

 superior-posterior, then all the parts of the cerebellum of the seal have been accounted 

 for. It may be noted that the part which I have just named the superior-anterior lobe 

 is reduced to a single folium in relation to the vermis, and it is this folium which is 

 named the folium cacuminis (fig. 2). 



Compared with the human cerebellum, it would appear that whereas in the seal the 

 vermis and its subordinate parts are well developed, and the flocculus, biventral lobe, 

 and tonsil are produced on a large scale, the remainder of the hemisphere is much 

 reduced in proportion. On the other hand, in man the hemisphere proper has become 

 much expanded and thickened, with corresponding reduction in the size of the flocculus, 

 the biventral lobe, and the tonsil. In fact, a theoretical enlargement of the superior- 

 anterior and superior-posterior lobes of the hemisphere of the seal, accompanied by their 



* Text-Boole of Anatomy, edited by CUNNINGHAM, 3rd ed., p. 512. 

 (ROY. soc. EDIN. TRANS., VOL. XLVIII., 844.) 



