CRURA OF THE CEREBRUM. 189 



The superficial set (fig. 56, f) are mostly horizontal, but some from the 

 upper margin of the pons descend obliquely over the others. 



The deep layer (fig. 57, f) is thickened, and contains much gray matter 

 between its fibres. 



The longitudinal fibres consist of two sets, viz., one from the anterior 

 pyramidal body ; and another from the lateral tract and the posterior 

 pyramid, to which a slip is added from the corpus olivare. The fibres are 

 not continued simply through the pons, but are increased in number by 

 the addition of others (peduncular) which, beginning in the upper two- 

 thirds of the pons, join them on the outer side. 



The fibres of the anterior pyramid (fig. 56, c) pass through the pons 

 between the two sets of transverse fibres, but not as one mass, for they 

 are divided into a number of small bundles in their progress. Much in- 

 creased in number, the fibres enter the crus cerebri at the upper border of 

 the pons, and construct that fasciculated surface of the peduncle (rf), which 

 is now uppermost. 



The fibres of the lateral column and posterior pyramid are altogether 

 deeper than the transverse fibres of the pons (fig. 57, rf), and are mixed 

 up with gray matter ; they are also more numerous than the preceding 

 set. They project close to the middle line, in the floor of the fourth ven- 

 tricle, and form the eminence of the fasciculus teres (fig. 55, 2 ) ; from that 

 spot they are continued upwards to the crus cerebri, of which they form 

 the deeper or cerebral part (fig. 57, d). In the pons a band from the 

 olivary fasciculus is added to these fibres. 



The olivary fasciculus (fillet, fig. 57) divides into two slips the pons. 

 One passes backwards to the upper (in this position deeper) part of the 

 crus cerebri, and ends in and beneath the corpora quadrigemina (p. 208). 

 The other is continued to the crus cerebri with the fibres of the lateral 

 column. 



Commissure of the pons. At the back of the pons there is a commissure 

 between the halves, opposite the deep longitudinal fibres. It consists, 

 like that of the medulla oblongata, of fine anterior-posterior and trans- 

 verse fibres. 



SECTION IV. 



DISSECTION OF THE CEREBRUM. 



THE cerebrum, or the great brain, is the largest of the subdivisions of 

 the encephalon, and weighs on an average 49 oz. in the male, and 44 oz. 

 in the female. It fills the upper part of the cavity of the skull ; and its 

 under surface would correspond with an oblique line on the head from the 

 eyebrow to the articulation of the jaw ; and from this point to the occipi- 

 tal protuberance. 



Taking the general form of the cranium, the cerebrum is convex on the 

 upper aspect, and uneven on the lower. It consists of two hemispheres, 

 which are placed side by side, and are partly separated by a median or 

 longitudinal fissure. Across the middle line the halves are united by cer- 

 tain interior parts (commissures), as well as by several connecting struc- 

 tures at the under surface. Superiorly the surface of the hemisphere is 



