224 Journal of Coi\ii'akati\e Neurology. 



extends forward far enough to cover a quarter of the cere- 

 brum. This portion is oval in transection with the longer 

 axis horizontal. Caudad, at the point of union with the 

 medulla, it expands to a width greater than that of the brain 

 at any other point. The two lateral lobes thus produced 

 contain white matter, chiefly in the form of fibres, passing 

 caudad into the medulla, and are to be considered as portions 

 of that body, homologous in part with the restiform bodies. 

 They lie farther caudad than the cerebellum proper, one on 

 each side of the fourth ventricle over about the middle of the 

 medulla. A small transverse fissure is present on the dorsal 

 surface of the cerebellum, a few millimetres cephalad of the 

 fourth ventricle. Between this fissure and the fourth ventricle 

 are transverse fibres passing apparently from one lateral lobe 

 to that on the opposite side. Cephalad of this fissure the grey 

 and white matter are arranged in the usual manner, the grey 

 filling the centre and enveloped by the white. White fibres 

 enter the cerebellum from below in the centre of the grey 

 matter and thus form a sort of arbor vitae, as in higher 

 animals. In the median line, about i mm. cephalad of the 

 to the caudal end of the cerebellum, a very narrow ventricle 

 arises from the aqueduct of Sylvius and passes dorsad into the 

 cerebellum for about two-thirds of the way to its dorsal 

 surface. With this exception the cerebellum is solid. 



The internal division, or volvula, lies in the aqueduct of 

 Sylvius immediately cephalad of the small ventricle of the 

 cerebellum. It presents the appearance of having been 

 formed by folding back upon itself through an angle of 90°, 

 not the entire cerebellum, as before, but merely the half 

 which lies cephalad to the cerebellar ventricle. It is as if 

 that half had projected much farther ventrad than the other 

 half, as a free lip, and had then been bent cephalad into a 

 horizontal position. Thus the grey matter which normally 

 lies next the cerebellar ventricle becomes ventral adjacent to 

 the aqueduct of Sylvius, and the white matter becomes dorsal 

 adjacent to the roof of the optic lobes. This volvula is about 



