An atlas of the medulla and midbrain / Edited by H.McE.K.

  • Sabin, Florence Rena, 1871-1953.
Date:
1901
Catalogue details

Licence: In copyright

Credit: An atlas of the medulla and midbrain / Edited by H.McE.K. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    mimis begins lias never been determined, but the model at least suggests tliiit this ridge is the junction of two different fibre sys- tems. The arch or commissure is to be seen in Figs. 2 and 7. In the latter the inner wall of the base of the ai*ch comes into sight. Just at the junction of the ])illars of the commissure with the fas- cicidus longitudinalis medialis and the proximal capsule of the nucleus ruber is the groove for the nucleus of Darkschewitsch. This groove has already been noted as opening out upon the superior capsule. The relative thickness of parts of the arch varies mark- edly. The ventral part contains most of the fibres. Dorsal to it is an area which shows no medullated fibres at all. The sections in this area, however, are decolorized more than the rest of the series. Jiist dorsal to this space is a naiTOw band of a few, fine, decussating fibres. These form relations, namely, the external and internal ridges and the lower limiting ridge, together with the arch over the canal, will make clear the direction of the tibres, as seen in sections. For example, be- tween the proximal, internal ridge and the lower limiting ridge, the fibres run in a longitudinal direction and form a definitel,y circumscribed, though narrow bundle (Figs. 5 and 6). At the limiting groove these fibres appear to break, and distal to the groove is situated the radix descendens (m) N. trigemini. This can be traced in Fig. 5 directlj- to the level of the main root of the N. trigeminus, -a point which is seen clearly in the model (Plate IV). In section (Fig. 6) the descending root of the nei^e is more broken, inasmuch as this is the level of its nucleus, of origin, which is situated in the locns cjeruleus. To return to the midbrain shell, the same two sections (Figs. and 6) will show that the external ridge is made up of fibres running in a wholly different direction. Indeed, they slant into the deep white from the formatio reticularis, so that while the internal border of the deep white is definite, the external border is extremely indefinite. These fibres from (or to) the formatio reticularis slant into the ridge and decussate in the commissure. Passing ventralward we come to a level in which no decussating fibres can be seen, but the external ridge continues to have the same struc- ture (Fig. 9). The next few sections, however, enter into the area of the decussation and the pillars of the arch (Figs. 11. 12 and 13). The section in Fig. IG passes through the micleus of Darkschewitsch at the base of the pillars of the arch. In the transverse series the stratum album profundum can be traced through Figs. 43 to .51. Certain points are brought out more clearly here than in the longitudinal series: (1) the fibres that slant into the ridge (Figs. 47 and 48), (2) the posterior com- missure and its relation to the niicleus of Darkschewitsch (Figs. 50 and 51) (Nu. c. p.). In regard to the course of these fibres the model confirms the find- ings of Held rather than those of TJamon y Cajal, the former stat-