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

  • Florence R. Sabin
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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    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. Thej' are to be distinguished from the fibres of the fasciculus longitudinalis medialis bj^ a dif¥erence in di- rection. The last section, Fig. 3, shows the decussation. By looking- at the nerve in the niodel from the side and from the dorsal aspect, the appearances in the transverse series can be readily predicted (Plates I and II). 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 16.' {d) N. oculomotorius.—^The X. ociilomotorius is the last of the median motor group to be considered. The position of its nucleus is best seen from the dorsal surface (Plate II), but the course of the root of the nerve and the relations must be followed in a view from the side (Plate III). The nucleus as seen in Plate II is a long mass of cells lying in the midbrain trough of the fasciculus longitudinalis medialis. The root-bundle passes directly ventralward near the middle line and emerges in the fossa interpedunculare. The posi- tion 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 JST. trochlearis; (2) that the nucleus itself is placed obliquely to a horizontal plane, so that the distal end is farther dorsal than the proximal. The oculomotor nerve is the only nerve in the central nervous system of which the nuclei of the two sides lie near enough together to be modelled as one. The nucleus as a whole consists of two lateral parts which are fused together in the ventral portion so as to make a gutter 3.1 mm. long for the median nucleus. The en- tire nucleus is 5.3 mm. long. ' 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 Kolliker, A., Handbuch der Gewebelehre, Bd. II, Leipz. (1896); also Van Gehuchten, A., Anatomic du systeme nerveux de I'homme, 2 ed., Louvain (189); and Barker, L. F., Tlie 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. VII. [1897], S. 439) describes the course as it is shown in the model.