248 THE RHOMBENCEPHALON. 



dividing the border of each hemisphere and the posterior end of 

 the worm. Rarely the two halves are not continuous through the 

 posterior extremity of the worm. In the horizontal sulcus the 

 remaining important sulci of the cerebellum terminate. They 

 are nearly parallel with one another; hence, the cerebellum is 

 laminated, not convoluted like the cerebrum. Though the 

 horizontal sulcus is an important landmark in the adult cerebellum, 

 it does not form a primary embryonic division of the cerebellum 

 but appears late in foetal life (Cunningham). 



SUPERIOR SURFACE OF THE CEREBELLUM. 



The superior surface of the cerebellum (fades cerebelli superior] 

 is bounded by the horizontal sulcus and the superior lamina of 

 the medullary body (Figs. 76 and 79). The posterior and larger 

 part of this surface is covered by the tentorium cerebelli, the 

 tentorial area; the small anterior part of it bounds the anterior 

 cerebellar notch. The superior surface is divided into rive con- 

 tinuous lobes by four crescentic sulci, called interlobular sulci. 



Sulci of Upper Surface. The interlobular sulci (sulci inter- 

 lobulares} divide the worm and both hemispheres into lobules; 

 and each lobe is composed of a central and two lateral lobules. 

 These sulci are best seen in a median section of the vermis and 

 are named in accordance with their relations to the lobules in the 

 worm, viz.: 



(1) The pre central sulcus (s. pracentralis], which is located 

 in the anterior cerebellar notch just above the superior velum 

 (Fig. 79). It is between the lingula and lobulus centralis, in the 

 worm; between the vinculum and ala, in the hemisphere. It 

 terminates in the horizontal sulcus. When the vinculum is 

 wanting the precentral sulcus is present only in the vermis. 



(2) The postcentral sulcus (s. postcentalis), in the worm, 

 separates the lobulus centralis from the culmen; and, in the 

 hemisphere, the ala from the anterior part of the quadrangular 

 lobule (Figs. 77 and 79). The sulcus is situated at the upper 

 border of the anterior cerebellar notch and runs just under the 

 anterior border of the tentorial surface of the cerebellar hemis- 



