The gray substance of the medulla oblongata and trapezium / by John Dean.

  • Dean, John, M.D.
Date:
[1864]
Catalogue details

Licence: Public Domain Mark

Credit: The gray substance of the medulla oblongata and trapezium / by John Dean. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    of multipolar cells noticed above. The further course of the roots will be best understood by reference to Plate XI, Fig. 40, representing a transverse section of the hypoglossal nucleus, on a level with the vagus nucleus and just above the calamus scriptorius. A portion of the fibres are connected with cells of the outer group (6), thus becoming united secondarily with the great bundles of fibres proceeding from the vagus, by which the hypoglossal nucleus is bordered anteriorly (D). By far the greater number, however, pass through these border fibres and cells, penetrating the nucleus, until they reach the groups lying in the central and posterior portion (h). A few fibres may be seen to leave the bundles, either just before or soon after they cross the border, and pass along with the latter towards the raphe, or else branch out into the anterior columns and join some of the numerous bundles passing towards the raphe, where they decussate with those coming from the opposite side (c). It is impossible to trace their further course. Numerous fibres, often forming consider- able bundles, may be seen either just as they enter the nucleus, or not unfrequently in its central region, sometimes forming quite a sharp curve (m,m), and bending back towards deeper lying cells, or towards the nucleus of the vagus, which some fibres from the hypoglossal certainly enter, forming a counterpart to the relation estab- lished, as noticed by Clarke1 and confirmed by my own observations, between some of the hypoglossal roots and those of the spinal accessory. The decussation of the hypoglossal roots, first pointed out by Kolliker, has recently been denied by Schroder van der Kolk. Kolliker2 states that there is a total decussation of the roots of both sides, on the floor of the fourth ventricle, so that those from one nucleus pass over into that of the opposite side. Lenhossek3 also makes a similar statement with regard to the inner nerve bundles. Clarke4 states that fibres from the hypoglossal bend inwards and decussate through the raphe with their opposite fellows. On the other hand, Schroder van der Kolk,5 after many investigations on different animals, as well as on the human medulla, was able to completely satisfy himself that this nerve does not decussate, but is lost entirely in the hypoglossal nucleus, being connected with multipolar cells by numerous fibres. He states, however, that the two nuclei are brought into connection by means of commissural fibres crossing the raphe and derived from the cells on each side. The question is by no means an easy one to decide; my first attempts at solving it led me to think that Schroder van der Kolk was right in his opinion, but in going over the whole ground again with very great care, and examining specimens from the medulla of man and various animals, prepared by different methods,6 I could have no doubt that some of the hypoglossal roots certainly decussate directly at the raphe, standing about in equal proportion to the main bundles as do those of * Philos Transactions, 1858, 252, 253 ; pi. xvii, fig. 35. ■ Mikroskopische Anatomic. II, 459. 8 Neue Untersnchungen, 32. * Philos Transactions, 1858, 253. 5 Medulla Spinalis and Oblongata, 1859, 97. * Especially specimens hardened in chromic acid and made transparent by turpentine, this method seeming to me decidedly the best for tracing the course of fibres.