INTEKNAL STEUCTURE. 



555 



The main lodif is derived from the anterior pyramid, fit)ra the fasci- 

 culi teretes, aud from the posterior pyramid. After it has passed 

 through the pons, and become increased in amount, it is separated 

 into two parts in tlie crus cerebri by a layer of dark cineritious matter, 

 named locus nigcr. The lower or superficial part, which is derived 

 from the anterior pyramid, consists almost entirely of white fibres, 

 collected into coarse fasciculi, and is named the crusfa or lasis, or the 

 fasciculated jmrtion of the peduncle (Foville) (fig. 388, g). It contains 

 also fibres from the nerve nuclei of the medulla, and from the middle 

 peduncle of the cerebellum. The upper part, composed principally of 

 the fasciculus teres and posterior pyramid, is named the tegmenfum (b). 

 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 from these bodies appear to pass to the 

 medullary substance of the hemispheres than are contained in the 

 crura. The actual continuity of the individual fibres spreading cut 

 in the hemisphere with those peduncular fibres which enter the sub- 

 stance of the thalamus and corpus striatum is doubted by many authors, 

 and among them, by Kolliker, who believe that the connection between 

 the fibres is effected by the branching cells of the ganglia. Some fibres 

 certahily pass by or through the ganglia, directly to the convolutions. The 



Fig. 3SS. — View op a Dissection of the Fig. 388, 



Fibres i.v the Left Cerebral Hemi- 

 sphere FROM below (after Mayo). 5 



The lower part of the temporo-sphenoidal 

 lolDe has been removed, a, the anterior and 

 a', the posterior part of the fillet of the 

 corpus callosum ; b, g, section of the eras 

 cerebri ; b, tegmentum ; ff, crust separated 

 from the last by the locus niger ; c', fibres 

 stretching from the back part of the corpus 

 callosum into the posterior lobe ; e, fasciculus 

 nncinatus connecting the anterior and middle 

 lobes across the Sylvian fissure ; /, /, trans- 

 verse fibres from the coi-pus callosum passing 

 into the cerebral hemisi^heres ; I, back part 

 of the thalamus ; in, corpus albicans ; q, 

 median section of the corpus callosum ; r, 

 radiating fibres of the hemispheres ; t, ante- 

 rior pillar of the fornix descending into the 

 corpus albicans (m) ; v, collateral fibres of 

 the convolutions ; X , anterior commissure. 



posterior fibres of the tegmentum 

 pass directly to the surface, as do also 

 those of the crus, which separate 

 the lenticular and caudate nuclei 

 of the corpus striatum. 



The assemblage of radiating fibres 

 in each hemisphere might be com- 

 pared to a fan, bent into the form 



of an incomplete hollow cone, having its concave surface turned down- 

 wards and outwards ; hence the name corona racliata applied to them 

 by Keil, and fibrous cone by Mayo (fig. 388). 



The accessory fibres of the peduncular system are as follows : — 



