466 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



Fig. 252. 



Fig. 252. Transparent transverse section of the pons of Man at the 

 level of its greatest convexity. The left half is made above, the right 

 half through, the plane of origin of the motor root of the fifth pair. 

 V) The upper medullary velum (valve of Vieussens), with the little 

 tongue over the fourth ventricle, which becomes enlarged below (con- 

 sequently on the right side of the figure) ; A, the transverse section of 

 the superior peduncle of the cerebellum in the lateral wall of the fourth 

 ventricle ; L, the posterior longitudinal fasciculus beneath the floor 

 of the fourth ventricle ; S, the inferior lamina of the fillet on the left 

 side, still covering the superior peduncle, and on the right presenting 

 a circular transverse section of medullary substance investing the 

 gelatinous substance (S) ; FM, the motor area of the posterior division 

 of the pons ; S', Reichert's fillet ; .Br, the middle crus, or pro- 

 cessus e cerebello ad pontem ; Tp, its deep ; Ts, its superficial trans- 

 verse fasciculi ; P, the transverse section of the crusta ; 5 m, the 

 nucleus of origin of the motor roots of the fifth, which run out- 

 wards through the arm of the pons (5) ; F, substantia ferruginea ante- 

 rior ; 5 6, fasciculi that, proceeding from the substantia ferruginea, 

 traversing and surrounding the posterior longitudinal fasciculi (L\ 

 pass transversely across the raphe, in order to form on the right side 

 the inner part of the descending roots of the fifth pair externally to the 

 posterior longitudinal fasciculi ; with these are associated on the right 

 side, surrounding the inner wall of the posterior longitudinal fascicu- 

 lus, the fibrse rectse of the raphe ; 5c, the external part of the descend- 

 ing roots of the fifth pair ; 5 d, portions of the great root of the fifth 

 which are superimposed upon the superior peduncle ; R, the raphe. 



