THE TUBER VALVUL^. 77 



removed, or a vertical section made through the organ, passing just to the outer 

 side of the pyramid. The biventral lobe is roughly triangular in shape, with 

 the base forwards abutting on the postnodular sulcus, and the apex directed 

 backwards and inwards towards the root of the pyramid. The outer side is 

 bounded by the outwardly curved pre-gracile fissure, the inner by the side of 

 the vallecula, but is concealed by the amygdala, which projects over the lobe. 

 The laminse have a curved direction radiating from the apex towards the base of the 

 triangle. The lobe is partly bisected by a fissure (midventral) deeper than the 

 rest, and becoming better marked towards the base. This fissure divides the lobe 

 into an inner and an outer portion ; from this subdivision its name has been 

 derived. Collectively, the pyramid, the connecting ridges, and the biventral lobes 

 constitute a distinct division of the cerebellum, to which the name lobe of the 

 pyramid may be applied. 



The tuber posticum and postero-inferior lobes : lobus tuberis. The 

 tuber valvulse seu posticum, which constitutes the hindermost division of the inferior 

 worm, exposes about five or six tertiary folia (laminse transversales inferiores) at 

 the surface between those of the pyramid and the folium cacuminis. It differs 

 from the other constituents of the inferior worm, and resembles those of the 

 superior worm in being obviously prolonged laterally into and gradually enlarging 

 to form the corresponding hemisphere lobes (fig. 58 B, t.v, l.t). These conjoined 

 postero-inferior lobes of the hemispheres with the tuber valvulas of the worm 

 collectively form a large alate mass (lobus tuberis}, bounded in front by the 

 anterior arcuate or pregracile fissure, which separates it from the pyramidal 

 (biventral) lobe ; behind by the great horizontal fissure, which also limits it 

 antero-laterally. Its laminae run in a curved manner, concentrically with these 

 fissures, and it is separated into four crescendo parts by three concentric fissures 

 two deep and complete, the middle arcuate and the posterior arcuate and a third 

 only slightly less deep, the lesser horizontal fissure. Of these four parts the two 

 anterior, about equal in size, form what has been termed the slender lobe (lobus 

 gracilis) ; the two posterior, of which the hinder one is the larger, together form 

 what has been termed the inferior seniilunar lobe. 



The whole cerebellar worm may thus be regarded as subdivided by deep sulci into nine 

 parts or lobes, each of which has a corresponding lobe of the hemisphere continuous with it. 

 This continuity is obvious upon the upper and posterior aspects of the organ, but on the inferior 

 aspect it tends to be rudimentary and is moreover concealed within the sulci valleculae. The 

 combined lobes which are thus formed by the continuity of the lobes of the worm with those 

 of the hemispheres are as follows : (1) lobus lingulas, (2) lobus centralis, (3) lobus culminis. 

 (4) lobus clivi, (5) lobus cacuminis, (6) lobus tuberis, (7) lobus pyramidis, (8) lobus uvulse, 

 and (9) lobus noduli. The hemisphere-parts of the lobus lingulas and of the lobus centralis 

 are rudimentary, but otherwise the hemisphere-parts of the lobes are considerably larger than 

 those of the worm, in some cases, as in that of the lobus cacuminis and the lobus tuberis. the 

 difference of size being very great. The former (lobus cacuminis) is, in fact, represented in 

 the worm by a single concealed folium only, while a large portion of the lobus tuberis, viz., 

 the lobus gracilis, can hardly be said to be represented in the worm. These nine lobes are 

 separated from one another by interlobar fissures, which are all nearly equally well marked in 

 the hemispheres, whilst in the worm some are less developed, particularly those above and 

 below the folium cacuminis. This median part of the lobus cacuminis is, therefore, 

 imperfectly marked off from the clivus above and the tuber valvulas below, the three together 

 forming a very distinct posterior subdivision of the worm. 



The relations between the parts of the worm and those of the hemispheres, and the fissures 

 which separate the several lobes from one another, as well as those which serve to subdivide 

 the lobus tuberis, are indicated in the accompanying table : 



