70 



THE CEREBELLUM. 



from the anterior part of each hemisphere the thick mass of the middle peduncle 

 passes forwards and inwards into the pons Varolii. Between the two superior 

 peduncles and behind the upper part of the 4th ventricle is a white lamina con- 

 tinuous with the white centre of the worm, which thins off into it. This is the 

 superior (or anterior) medullary velum or valve of Vieussens ; it extends as far as 

 the corpora quadrigemina, filling up the interval between the superior peduncles, 



for.Mon 



forni 



traneu.figg. 



pineal stria 

 post. comm. 

 pineal 



ileniitm 



monttcwlu.8 



ualu 



pjrar 



Fig. 57. PORTION OF A MEDIAN SECTION OF THE BRAIN, SHOWING THE CORPUS CALLOSUM, THIRD 



VENTRICLE, AQUEDUCT AND FOURTH VENTRICLE, PONS, CEREBELLUM, &C. (G. D. T.) 2 



and becoming continued into the roof of the aqueduct of Sylvius. Below, there is 

 a similar white lamina prolonged under and on either side of the nodule from the 

 white centre, and stretching over this part of the ventricle towards its lateral 

 boundaries (fig. 56, p v). It does not, however, extend far down, but ends with a 

 somewhat thickened margin, concave downwards, being prolonged towards the 

 calamus scriptorius merely by the ventricular epithelium, which covers its ventral 

 surface. To the semilunar lamina thus formed the name inferior (or posterior) 

 medullary velum is applied. 



The hemispheres are separated below and behind by a deep notch (posterior 

 ccrebellar notch, incisura marsupialis), and above and in front by a broader, shallower 

 notch (anterior cerebellar notch, incisura semilunaris). The upper vermiform process, 

 although slightly elevated, is not sharply marked off from the dorsal surface of the 

 hemispheres, so that the upper surface of the organ, which is on the whole flattened 

 but somewhat ridged in the middle (culmen monticuli), slopes downwards uninter- 

 ruptedly cii each side and behind (clivus). On the inferior surface each hemisphere 

 is convex both from before backwards and from side to side, but is separated 

 from its fellow by a deep median fossa, named the vallecula, which is continuous 

 behind with the posterior notch, and in which the inferior vermiform process 

 (fig. 56, c to n, fig. 58 B, t.v. to n.) lies concealed. Into this hollow the medulla 

 oblongata is received in front, and the falx cerebelli behind. 



