STRUCTURAL ARRANGEMENTS OF CEREBRUM 425 



and in the crusta is shown in the accompanying diagrams (Figs 215 

 and 216). 



The fronto-pontine and temporo-pontine fibres, which end in the nucleus 

 pontis, come there in relationship with the fibres forming the middle peduncles 

 of the cerebellum and derived chiefly from the 

 lateral lobes of the cerebellum. These fibres 

 may therefore be regarded as the efferent 

 side of the great cerebro-cerebellar connections 

 of which the afferent side is represented 

 by the fibres efferent so far as concerns 

 the cerebellum which pass from the cere- 

 bellar cortex to the dentate nucleus and 

 thence by a fresh relay in the superior cere- 

 bellar peduncles to the red nucleus, optic thala- 

 mus, and cortex of the opposite side. The 

 development of these fibres, as of the lateral 

 lobes of the cerebellum, is largely proportional 

 to the growth of the cerebral hemispheres. In 

 cases where there has been congenital atrophy of fifth nerve; P, fillet (I, lateral, 



e -i i i i j_ i e 1 1 an( i m > mesial fillet) ; Pyr, pyra- 



of one cerebral hemisphere the crusta of the mid ; Fr. fibres from frontal lobe 

 same side and the lateral lobe of the cerebellum 

 of the opposite side also fail to develop. 



ill 



FIG. 216. Transverse section 

 through mid-brain to show 

 position of fillet and pyramid. 

 AQ, anterior corpus quadri- 



geminum ; dV, descending root 



to pons; TO, fibres from tem- 

 poral and occipital lobes to 

 pons ; Ne, fibres from nucleus 

 caudatus to pons ; III, root of 

 third nerve ; S, Sylvian iter; 

 Rn, red nucleus. 



II. ASSOCIATION FIBRES 

 These fibres serve to unite different por- 

 tions of the cortex of the same hemisphere and may be classified into 

 short and long association fibres. The short association fibres pass round 

 the bottom of the sulci in U-shaped loops connecting adjacent convolutions. 



FIG. 217. Chief association bundles of the cerebral hemispheres. (CUNNINGHAM.) 

 A. Outer aspect of hemisphere. B. Inner aspect of hemisphere. 



These fibres are some of the latest to acquire a medullary sheath .and 

 probably first become functional as associated activity between the various 

 portions of the cortex is gradually acquired by education. 



The long association fibres may be divided into five groups as follows : 

 (a) The uncinate fascic'idus passes from the orbital convolutions of the frontal lobe 

 to the front part of the temporal lobe round the stem of the Sylvian fissure (Fig. 217). 



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