An atlas of the medulla and midbrain : a laboratory manual / by Florence R. Sabin ; edited by Henry McE. Knower.

  • Florence R. Sabin
Date:
1901
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Licence: In copyright

Credit: An atlas of the medulla and midbrain : a laboratory manual / by Florence R. Sabin ; edited by Henry McE. Knower. Source: Wellcome Collection.

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    metrical. On the side of the single nucleus the fibres have a larger and more ventral superficial origin than those of the other side. The course of the fibres can be traced in the longitudinal series in the following sections: Figs. 12-10 show the nucieus and its relation to the fasciculus longitudinalis medialis. It will be noticed that the section in Fig. 12 shows no root-fibres, since it passes through the ventral por- tion of the nucleus. The root-fibres can be followed through the rest of the series from Fig. 10 to Fig. 3. They are to be distinguished from the fibres of the fasciculus longitudinalis medialis by a difference in direction. The last section, Fig. 3, shows the decussation. By looking at the nerve in the model from the side and from the dorsal aspect, the appearances in the transverse series can be readily predicted (Plates 1 and 111). The most distal section would show the decussation, while each succeeding section would show two or three small bundles cut across or slightly obliquely, and occurring a little farther ventral in each section until the level of the nucleus is reached, and here the fibres would turn directly medialward. This course can be followed in the following series, Figs. 41 to 46.1 last of the median motor group to be considered. The position of its nucleus is best seen from the dorsal surface (Plate m1), but the course of the root of the nerve and the relations must be followed in a view from the side (Plate 1v). The nucleus as seen in Plate mt is a long mass of cells lying in the midbrain trough of the fas- ciculus longitudinalis medialis. The root-bundle passes directly ventralward near the middle line and emerges in the fossa inter- pedunculare. The position of the nucleus in the trough of the fasciculus longitudinalis medialis determines two facts: (1) that the nucleus as a whole lies farther ventral than the nucleus N. trochlearis; (2) that the nucleus itself is placed obliquely to a horizontal plane, so that the distal end is farther dorsal than the proximal. 1 The root-fibres have been described as making a double bend, passing at first dorsalward, then spinalward, and again dorsalward at a right angle. Cf. von K6lliker, A., Handbuch der Gewebelehre, Bd. u, Leipz. (1896); also Van Gehuchten, A., Anatomie du systéme nerveux de VPhomme, 2 ed., Louvain (1897); and Barker, L. F., The Nervous System and its Constituent Neurones, N. Y. (1899), p. 938, et seq. This course does not appear on the model, which shows a gradual dorsal curve from the very start. Such an angle was not suggested in either of my series but there is no doubt that it might be missed in building the model. The matter might be settled by referring to sagittal sections. On the other hand Forel (Arch. f. Psychiat., etc., Berl., Bd. vi [1897], S. 439) describes the course as it is shown in the model. N. tv in sections,