THE BKAIX IX THE EDENTATA. 337 



and upon tlie posterioi- suiface of the organ it extends as far as the ventral surface. 

 Mesially it becomes continuous, by means of a very narrow stalk, with the small folium 

 which extends across the mesial plane above the pyramid and is included between the 

 fissures a and c. The surface of the area C is deeply incised by about 12 fissures, which 

 are obliquely placed and converge toward the mesial stalk. 



The area B is by far the greatest of the three subdivisions of the area cresceiis. It is 

 attached to the mesial parts of the organ by a narrow stalk, composed of a single folium, 

 which is wedged in between the areas A and C, but it rapidly expands in the lateral 

 direction and forms a large oval mass, which extends obliquely forward between the lohus 

 flocciili on the lateral side, and the area A and the lobus anticus on the mesial side, and 

 reaches as far as the columna cerebelll. The siu-face of this area, which forms the 

 nucleus of tlie large lateral mass of the cerebelhrm, is deeply scored by numerous fissures, 

 which converge toward the axis of the area, and ihus this region becomes spHt up into 

 innumerable folia, which are arranged like the barbs on a feather. The sinale folium 

 which forms the stalk oi this large mass expands in the middle line to form a little 

 cuneiform mass whicli is interposed between the mesial continuations of the fissures 

 a and b. 



We find, therefore, that it is possible to divide the lobns centralis, according to the 

 conventional mode, into a distinct central part, or vernus, and lateral areas. In the 

 case of the lobus anticus there is no such natural division. And in the case of the lobus 

 2J0sficus the whole lobe belongs to tlie ceniiis. 



The importance of this mode of dividing vip the cerebellum into vermis and lateral 

 lobes is very much exaggerated by the customary mode of describing the organ. 



The bilateral symmetry of the vermis is disturbed by bending to the right side, which 

 aff'ects the upper part of the pyramid and the adjacent supra-pyramidal part of the 

 central lobe. 



The study of the configuration of the cerebellum as it is demonstrated in a mesial 

 sagittal section is esj)ecially instructive. In Orycteropus the mesial sagittal section of 

 the cerebellum exhibits an oblong figm-e with all the angles, except the postero-inferior, 

 rounded off. The dorsal and ventral surfaces are horizontal and considerably longer than 

 the vertical anterior and posterior surfaces. 



The arrangement of the lobes and their subdivisions, which is exposed in a mesial 

 sagittal section of the cerebellum in Orycterojius, presents the closest analogy to that of 

 the human cerebellum. If we overlook the fact that the general shape of the sections 

 is so different, and that the diameters of the former section are only about one half those 

 of the latter, we might confidently say that the sections are in all essentials identical. 

 This fact is so impressive and significant that y\e muy be pardoned for examinins the 

 points of this resemldance more closely. 



We may begin at the velum medullare and lollow the folia in the caudal direction in 

 the two forms, employing the terms in common use in human anatomy at the present 

 time (cp. Quain's, Schwalbe's, or any of the ordinary anatomy text-books). 



The most caudal part of the velum is thickened by transverse bands of grey matter 

 to form the liinjula in both brains. The rest of the lobus anticus presents a very close 



50* 



