244 THE RHOMBENCEPHALON. 



lower halves being separated by an antero-posterior groove, 

 called the valley or vallecula cerebelli. The upper surface of the 

 vermis is called the superior worm, or vermis superior; and the 

 lower surface, the inferior worm, or vermis inferior. The superior 

 and inferior surfaces are separated from one another at. the pos- 

 terior end of the worm by the great horizontal sulcus; ante- 

 riorly, the medullary body of the cerebellum separates them. At 

 either end of the worm is a notch bounded by the vermis and 

 the hemispheres, the anterior and posterior cerebellar notches. 



The posterior cerebellar notch, incisura cerebelli posterior 

 (Fig. 76), bounded by the posterior end of the worm and the 

 postero-medial border of the hemispheres, is occupied by the 

 falx cerebelli. A prolongation of the medullary body of the 

 cerebellum fills up the incisura cerebelli anterior, or anterior 

 cerebellar notch, which is situated between the antero-medial 

 borders of the hemispheres in front of the vermis cerebelli. 



The medullary body (corpus medullare} which is the white 

 center of the cerebellum splits, in its median part, into two lamina: 

 a superior, which forms the superior medullary velum and three 

 pairs of connecting bands (peduncles), and an inferior, which is 

 the inferior medullary velum (Figs. 79 and 78). Separating at an 

 acute angle, the two laminae form the tent of the fourth ventricle. 



The inferior medullary velum (velum medullare inferius, Figs. 

 79 and 91) is the inferior lamina of the medullary body. It 

 is a short plate of white matter, not more than a quarter of an 

 inch long and is separated from the superior lamina by the angle, 

 called the fastigium. It ends in a concave border from which a 

 sheet of epithelium continues down over the fourth ventricle; 

 and together they form the inferior half of the roof of that cavity. 

 Laterally, the inferior velum extends to the flocculus of the hemis- 

 phere. Of the worm it covers the nodulus, antero-superiorly. 

 It bounds, dorsally, the lateral recesses of the fourth ventricle. 



In the BNA the cerebellar vela are called " velum medullare anterius" and 

 " v. m. posterius;" but there is no more reason for those embryological terms 

 in this place than there is elsewhere throughout the central nervous system, 

 and I have used "superius" and " inferius " which properly indicate their 

 positions in adult anatomy. 



