THE CEREBELLUM. 



1087 



it is seen at the bottom of the vallecula between the median areas of the biventral lobules, 

 where it forms the most prominent division of the worm. It is an elongated club-shaped 

 mass, attached by a narrow stalk and separated from the adjacent parts of the worm by the 

 prepyramidal and postpyramidal fissures and from the hemispheres by the sulci valleculae. 

 The convex inferior surface usually presents from 5-8 superficial folia, those towards the 

 uvula being longer than those directed towards the tuber. After removal of the tonsil, a 

 narrow band, the connecting ridge, is seen passing, on each side, from the anterior part of the 

 pyramid to the adjacent mesial end of the biventral lobe, which, in this manner, is brought into 

 relation with the worm. 



The biventral lobule (lobulus biventer) ordinarily consists, as its name implies, of two sub- 

 divisions, which together appear on the surface as a curved zone, the extremities of which are 

 more contracted than the intermediate tract that attains a breadth of 15 mm. and more. The 

 details of form and foliation are quite variable, the lobule being not only sometimes much 

 broader than usual, but farther subdivided, so that three, instead of two, tracts are inducted. 

 The broader outer end of the lobule reaches the anterior margin of the hemisphere, and the 

 narrowed inner end the vallecula, in consequence of which the component superficial concentric 

 leaflets, some twelve to sixteen in number, are compressed and thinner as they approach the 

 sulcus valleculae. The biventral lobule is separated from the tonsil, around which it curves, by 

 the lateral extension of the prepyramidal or post-tonsillar fissure and is limited behind by the 

 arched postpyramidal fissure. 



Lobus tuberis. — The tuber (tuber vermis) forms the most posterior division of the 

 inferior worm and lies beneath the great horizontal fissure when that sulcus is continuous 

 across the mid-line. When the folium cacuminis is small and buried, the tuber comes 

 into close relation with the lower end of the clivus, the three divisions of the worm just 

 mentioned all springing from a common stalk of white matter. The tuber is of a general 



Fig. 941. 



Roof of fourth ventricle 



Superior cerebellar peduncle 

 Middle cerebellar peduncle 

 Flocculus 



Great 

 horizontal fissure 



Superior worm 

 (lobulus centralis) 



Nodule 



Postero-inferior 

 lobule 



Biventral lobule 

 Position of removed tonsil 



Inferior medullary velum 

 Uvula 

 Furrowed band 



Pyramid 



Tuber 

 Cerebellum, seen from below after removal of tonsils. 



conical form, with the base directed towards the pyramid, from which it is separated by the 

 postpyramidal fissure, and its apex projecting into the posterior cerebellar notch. It presents 

 a few, from 2-4, superficial folia, which model the posterior pole of the worm, as viewed from 

 behind and above. 



The tuber is directly connected on each side with a considerable crescentic tract, the 

 postero-inferior lobule (lobulus semilunaris inferior), that is limited in front by the lateral 

 extension of the postpyramidal fissure (sulcus inferior anterior) and behind by the great hori- 

 zontal fissure. After emerging from the sulcus valleculae, the folia rapidly expand into 

 a lunate tract, from 15-25 mm. in its widest part, that forms the immediate posterior border 

 of the hemisphere. The postero-inferior lobwle is usually described as divided into two 

 parts, an anterior and a posterior, by the postgracile fissure (sulcus inferior posterior), but 

 quite frequently further subdivision of the superficial folia, from 12-18 in number, results 

 in defining three sublobules. The anterior of the two conventional subdivisions is a narrow 

 tract of fairly uniform width to which the name lobulus gracilis is applied. The lunate 

 posterior area, much less regular in contour and foliation, is known as the inferior crescentic 

 lobule (lobulus semilunaris inferior) and sometimes presents evidence of subdivision into 

 two secondary crescentic areas. The postero-inferior lobules and the tuber constitute the 

 lobus tuberis. 



