576 



THE NEEVOUS SYSTEM. 



laterally, is traversed by two or it may be three curved fissures. The most anterior 

 of these cuts off a narrow, curved strip of cerebellar surface, which presents a more 

 or less uniform width throughout its whole length. This is the so-called lobulus 

 gracilis. 



The pyramid is connected with the biventral lobule on each side by an elevated 

 ridge which crosses the sulcus valleculae. The term lobus pyramidis is applied to 

 the three lobules, which are thus associated with each other. 



The uvula is a triangular elevation of the vermis inferior. It lies between the 

 two tonsils, and is connected with each of these by a low-lying band-like ridge 

 of gray matter scored by a few shallow furrows, and in consequence termed the 

 furrowed band. The two tonsils and the uvula form the lobus uvulae. 



.Central lobule Anterior medullary velum 

 Brachiuru coniunctivum ' Ala lobuh cen 



Brachium pontis^ 



Fourth ventricle 



Uvula- 

 Horizontal fissui 



Postero-inferior lobule 



Postero-inferior lobule 



Lobulus gracilis 



Biventral lobute 



Pyramid Tuber vermis 



FIG. 510. INFERIOR SURFACE OF THE CEREBELLUM. 



The right tonsil has been removed so as to display more fully the 'posterior medullary velum and 



the furrowed band. 



The nodule and the flocculus of each side are linked by a delicate connect- 

 ing lamina which is formed by the posterior medullary velum. 



THE STRUCTURE AND CONNEXIONS OF THE CEREBELLUM. 



Arrangement of the Gray and White Matter of the Cerebellum. The white 

 matter of the cerebellum forms a solid compact mass in the interior, and over 

 this is spread a continuous and uniform layer of gray matter. In each hemi- 

 sphere the white central core is more bulky than in the vermis, in which tl 

 central white matter is reduced to a relatively thin bridge thrown aci 

 between the two hemispheres. When sagittal sections are made through the 

 cerebellum, the gray matter on the surface stands out clearly from the white 

 matter in the interior. Further, from all parts of the surface of the central core 

 stout stems of white matter are seen projecting into the lobes of the cerebellum. 

 From the sides of these white stems secondary branches proceed at various angles, 

 and from these again tertiary branches are given off. Over the various lamellae 

 of white matter thus formed the gray cortex is spread, and the fissures on the 

 surface show a corresponding arrangement, dividing up the organ into lobes, 

 lobules, and folia. When the cerebellum is divided at right angles to the general 

 direction of its fissures and folia, a highly arborescent appearance is thus presented 

 by the cut surface. To this the term arbor vitae is applied. 



Nucleus Dentatus and other Gray Nuclei in the White Matter of the 

 Cerebellum. Embedded in the midst of the mass of white matter which forms the 

 central core of each hemisphere there is an isolated nucleus of gray matter, which 

 presents a strong resemblance to the inferior olivary nucleus of the medulla. 

 It is called the nucleus dentatus, and it consists of a corrugated or plicated lamina 



