556 



THE CEREBRUM. 



peduncular fibres, which pass up from the medulla oblongata to the hemispheres, 

 and constitute the peduncles of the cerebrum. These fibres increase in number as 

 they ascend through the pons, and still further in passing through the optic thalami 

 and striated bodies, beyond which they spread in all directions into the hemispheres. 



2. Transverse or commissural fibres, which connect the two hemispheres together. 



3. Longitudinal or collateral fibres, which, keeping on the same side of the middle 

 line, connect more or less distant parts of the same hemisphere. 



1. In each hemisphere the peduncular fibres consist of a main body and of certain 

 accessory bundles of fibres. 



The main body is derived from the anterior pyramid, from the fasciculi teretes, 

 and from the posterior pyramid. After it has passed through the pons, and be- 

 come increased in amount, it is separated into two parts in the crus cerebri by a 

 layer of dark cineritious matter, named locus niger. The lower or superficial part, 

 which is derived from the pyramid, consist almost entirely of white fibres, col- 

 lected into coarse fasciculi, and is named the crust or basis, or the fasciculated por- 

 tion of the peduncle (Foville). The upper part, composed principally of the fasci- 

 culus teres and posterior pyramid, is named the tegmentum. It is softer and finer in 

 texture, and is mixed with much grey matter. 



Still increasing in number within the peduncle, these two sets of fibres ascend to 

 the thalamus and corpus striatum. A much larger number of fibres diverging 



Fig. 370. Fig. 379. POSTERIOR VIEW 



OK THE PEDUNCLES OF TUN 

 CEREBRUM AND CEREBEL- 

 LUM (after Arnold). f 



The lower and fore part of 

 the cerebral hemispheres is 

 preserved, the cerebellum is 

 completely detached from its 

 peduncles, and on the right 

 side the corpora quadrigemina 

 and thalamus opticus have 

 been dissected, a, fasciculus 

 teres of the left side ; b, fibres 

 of the tegmentum ascending 

 through the right thalaraus ; 



c, left corpora quadrigemina ; 



d, lateral column of the cord ; 



e, restiform body ; /, superior 

 peduncles of the cerebellum ; 

 g, fibres of the crust ; i, ?', 

 the fillets ; k, k, corpora 

 stria ta ; Z, the left thalamus ; 

 m, m, sections of the middle 

 peduncles of the cerebellum ; 

 n, section of the left inferior 

 peduncle ; p, left postei'ior 

 pyramid ; g, section of the 

 corpus callosum ; s, under 



surface of the same, and below it the cavity of the fifth ventricle ; e, left anterior pillar 

 of the fornix; y, decussation of the radiating fibres with the crossing fibres of the corpus 

 callosum. 



from these bodies appear to pass to the medullary substance of the hemispheres ; but 

 the actual continuity of the individual fibres spreading out in the hemisphere with 

 those ascending to the thalamus and corpus striatum is doubted by many authors, 

 and among them, by Kolliker. 



The assemblage of radiating fibres in each hemisphere might be compared to a 

 fan, bent into the form of an incomplete hollow cone, having its concave surface 

 turned downwards and outwards ; hence the name corona radiata applied to them 

 by Reil, and fibrous cone by Mayo. 



