ORIGIN OF THE CEREBRAL NERVES. 489 



versely through, and partly behind them, and attach themselves 

 to the fifth to form the innermost of those of its roots, which are 

 covered by the grey floor of the fourth ventricle, being situated 

 between the posterior longitudinal fasciculi and the middle 

 descending roots (figs. 252, on the right side,Z; 253, on the left 

 side, EL). The transverse decussating fasciculi of the middle, 

 and the straight fasciculi of the internal, descending roots, do 

 not appear to mingle in the raphe', but the former, bending to 

 make way for the latter, pass above them. The internal de- 

 scending roots are continuous with the formations of smaller 

 nerve corpuscles situated in front of and behind the longitudinal 

 fasciculi. 



Stilling derived the two last-mentioned portions of the origin of the 

 fifth simply from the grey substance of the floor. I myself formerly 

 attributed their origin to radiating fibres from the medulla of the 

 hemispheres, which associate themselves externally, above the planes 

 of section represented in fig. 248, below the optic thalami, with the 

 posterior longitudinal fasciculus, and descend with it. Inasmuch as 

 these fasciculi extend downwards between the external descending 

 root of the fifth and the posterior longitudinal fasciculus, from which 

 region so important an addition passes to the great root of the fifth, 

 I formerly regarded them as portions of this root. But after I had 

 acquired a knowledge of the mode in which the medullary fibres 

 proceeding from the substantia ferruginea reach beneath the grey 

 floor of the opposite side, I comprehended that those lateral posterior 

 fasciculi of the tegmentum, externally to the posterior longitudinal 

 fasciculi, were indeed covered and interlaced by the actually descending 

 roots of the fifth, but could not constitute the roots of the fifth. 



3. A root of the fifth, the nucleus of origin of which is situ- 

 ated below the plane of emergence (ascending root of the fifth). 

 Corresponding to the point of emergence of the fifth (fig. 253, 

 Q), external to the tegmentum and internal to the fibres from 

 the cerebellum, as far as to the lowest segments of the me- 

 dulla oblongata, is a compressed mass of transversely divided 

 fibres, the extremities of which must obviously lie in the origin of 

 the fifth (figs. 254, 255, 256, 257, 258, S G). The sectional area 

 of these fibres includes in its concavity, which is turned back- 

 wards, grey matter containing for the most part small nerve 

 corpuscles, in which, after breaking up into delicate fasciculi, 



