INTERNAL STRUCTURE. 



519 



ance, named arhor vita {a v, fig. 363, SSl'i. This appearance is seen in 

 any vertical section, but it is most perfect in that which passes through 

 the median plane, where the relative quantity of the central white 

 matter is small. The foliations are arranged somewhat pinnately, 

 the section of each primary lamina having those of secondary laminse 

 clustered round it like leaflets on a stalk. 



In the lateral hemispheres, where the peduncles enter, the white 

 matter is more abundant ; and, if a section be made through either 

 hemisphere half way between its centre and the middle of the vermi- 

 form process, it will display a nucleus of grey matter, which is named 

 the corpus dentatum of the cerebellum {c d). This structure, very 

 similar to that already described in the olivary body of the medulla 

 oblongata, presents the appearance of a waved line of compact yellowish 

 brown matter, surrounded by white substance and containing Avhitish 

 matter within. This line is interrupted at its upper and inner part. 

 In whatever direction the section is carried through the corpus den- 

 tatum, this waved line is seen, so that the dentate body may be 

 described as consisting of a plicated pouch or capsule of grey sub- 

 stance open at one part and inclosing white -matter in its interior, like 

 the corpus dentatum of the oHvary body. White fibres may be traced 

 from it to the superior peduncles of the cerebellum and to the valve of 

 Vieussens. 



Fig. 364. — View of a Dissection 

 OF THE Fibres op the Medull.i 

 Oblongata and Pons Varolii 

 (from Arnold). | 



i, the anterior pyramid ; I', its 

 fibres traced iipwards through tlie 

 pons Varolii ; c, olivary column ; d, 

 olivary body ; m, superficial trans- 

 verse fibres of the pons on its left 

 side ; m', the deeper transverse 

 fibres of the right side ; m', the 

 prolongation of these fibres as middle 

 peduncle of the cerebellum ; p, q, 

 their continuation into the laminre 

 and folia of the cerebellum ; n, in- 

 ferior peduncle ; x, the decussating 

 part of the left lateral column cross- 

 ing to the right anterior pyramid. 



Fig. 36-1. 



The fibres in the primary lamella can be traced continuously from the peduncles 

 of the cerebelliun. Upon these central jilates are laid other coUatrrnl JamcJlcp, 

 which are not connected with the fibres proceeding from the middle of the 

 cerebellum, but merely pass from one folium to another. 



The grey matter is not uniform throughout its whole thickness, but is com- 

 posed of two or more layers differing in colour and other characters ; — resem- 

 bling, in this respect, the cortical substance of the posterior convolutions of the 

 cerebrum. 



The fibres composing the peduncles of the cerebellum are an-anged in its 

 interior in the following manner. The middle peduncles, which are the most 

 superficial, enter the lateral parts of the cerebellum ; they may be traced into the 

 folia of these parts, and form a large part of each hemisphere (fig". 3G4, m"^. The 

 inferior peduncles (fig. oG.o, n rf) pass upwards into the middle part of the cere- 

 bellum, in the folia of which they are distributed, especially in those of the upper 

 surface. The superior peduncles (r; see also fig. 3.58), which are placed nearest 

 to the middle line, are piincipally connected with the folia of the inferior vermi- 



