1084 



HUMAN ANATOMY. 



on the worm, and cuts deeply into the lateral and posterior portions of the hemispheres 

 and the worm behind. It is, however, visible on the upper aspect of the cerebellum 

 only for a short distance as it approaches the posterior notch, the remainder of its 

 course being masked by the overhanging border of the hemisphere. Although 

 of cardinal importance in the usual description of the human cerebellum, the great 

 horizontal sulcus is of secondary morphological significance, being a secondary 

 fissure that is developed relatively late in man and feebly or not at all in many 

 other animals. 



Both the vermis and the hemispheres are subdivided into tracts, or lobules, by 

 the deeper fissures ; these are grouped into lobes, in the conventional division of 

 the human cerebellum, by regarding each median division of the worm as associated 

 with a pair of lateral lobules, one for each hemisphere. 



Lobes and Fissures of the Upper Surface. — The subdivisions of the 

 superior worm are, from before backward : — (i) the lingula, (2) the lobzdus centralis, 

 (3) the culmen, (4) the clivus, and (5) the folhim cacuminis. With the exception 

 of the lingula, which usually is unprovided with lateral expansions, these median 

 tracts are connected respectfully with (2) the al(e lob2di centralis, (3) the anterior 

 crescentic lobule, (4) iho. posterior crescetitic lobule, (5) the. postero-snperior lob7ile. 



Lobus Lingulae. — The lingula, the extreme anterior end of the superior worm, is not free, 

 but lies attached to the upper surface of the superior medullary velum, covered by the over- 

 hanging adjacent part, lobulus centralis, of the worm, which must be displaced to expose the 



Fig. 939. 



Ala lobuli ceijlralis 



Anterior notch 



Lobulus centralis 



Anterior 

 crescentic lobule 



Posterior 

 crescentic lobule 



Postero-superior 

 lobule 



tcentral fissure 



Inien 



Preclival fissure 



Postclival fissure 



Folium cacuminis 



Great horizontal fissure 



Postero-inferior lobule 



Posterior 

 notch 



Tuber 



Cerebellum viewed from above. 



Structure in question. The lingula consists of a tongue of gray matter, composed of five or six 

 rudimentary transverse folia, that overlies the median and lower part of the superior medullary 

 velum and, therefore, is behind the upper part of the fourth ventricle (Fig. 938). Occasionally 

 the lingula is prolonged laterally by rudimentary folia onto the superior cerebellar peduncles, in 

 which case these extensions, known as the alse lingulae (vincula lingulae) are reckoned as the 

 lateral divisions of the lobus lingulae. 



Lobus Centralis. — The median part of the subdivision includes the second segment of the 

 upper worm, the central lobule (lobulus centralis), that lies chiefly at the bottom of the anterior 

 notch and is visible to only a very limited extent on the upper surface of the cerebellum. The 

 central lobule consists of from 15-18 folia, but not infrequently is divided into two sets of leaflets, 

 which then are collectively somewhat more numerous. It is separated from the lingula by the 

 precentral fissure and from the culmen by the postcentral fissure. On each side the central 

 folia are prolonged into a triangular tract that curves along the side of the anterior notch, form- 

 ing a lateral wing-like lobule, the ala (ala lobuli centralis). The two alae, in conjunction with 

 the median worm-segment, constitute the lobus centralis. 



Lobus Culminis. — The third division of the upper worm includes the most prominent part 

 of the upper surface of the hemisphere and, being the crest or summit of the general elevation, 



