Abstract from notes on the minute structure of the spinal cord / by John B. Trask.

  • John Boardman Trask
Date:
1860
Catalogue details

Licence: Public Domain Mark

Credit: Abstract from notes on the minute structure of the spinal cord / by John B. Trask. 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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    [6] and results from our manipulations; when we consider how fragile and deli- cate is the organ, the extreme tenuity of the sections, and that the canal is formed of a membrane more dense than the columnar and commissural parts surrounding it, and that an almost inappreciable inequality in its sections could not do otherwise than induce a degiee of distortion, it is not a valid objection to the exis'ence of the canal that it does not always present a per- fectly symmetrical outline. The maximum capacity of the canal seems to be attained in the region of the dorsal enlargement, and is much diminished in the lumbar portions, but is not so small in the latter as in the upper cervical, between the first and second vertebrae ; in this region the diminution in size is most particularly marked. As to the form of the canal in the normal condition, it is somewhat diffi- cult to determine it with absolute accuracy, for the reasons given on a pre- ceding page, viz. : the difference in density of the membrane of the canal and surrounding parts, the distortion arising from corrugation in the harden- ing process thus casting some doubt on its true shape during life. There is, however, a uniformity in its appearance under the different reagents used on sections from the same region of different cords, and from the features which it presents to my ^^ew under the varied conditions in which I have examined it: it may be considered as having the form of an obtuse elHpsoid in the dor- sal region, the major axis of which is transverse to the antero-posterior median line. These remarks apply to a general outline only. To be more specific, it is necessary to state that the form above given of the opening of the canal has a constant modification of the ellipsoid, as follows: antero-posteriorly are two processes formed by reflections of the tissue of the anterior commissure, the posterior and anterior terminations of which are acute; the anterior portions of these processes are the largest, and extend nearly to the peripheral surface of the cord; in fact, they become one of the long processes produced toward the outer surface of the cord from the anterior cornua, but not as given in Stilling's figure as laid down by Dr. Todd, page 706, Ency. Anat. and Phys., Vol. IH. On each side.of the antero-median line, and lying between these processes, are two rather broad and shallow sulci; the concave surfaces of which are directed toward the anterior columns of the cord. These sulci destroy the regularity of the ellipsoid form of the canal, thus making it an irregular ellipsoid, from the depressions in one of its sides formed by the sulci, and which are lateral to its minor axis. The membrane of the canal is easily examined in good sections of the cord. It has all the features of a serous tissue, and lines the entire course of the cavity. I am inclined to the opinion that in the normal state, during life, its inner surface is not smooth, but more or less folded, for on a careful examination it is found that the rugne so very distinctly marked on its inner surface correspond to the process-like prolongations of this membrane thrown out from every part of its border exteriorly. These prolongations of the membrane give to the immediate region about the canal the appearance of a zone of rays entirely encompassing the opening. From the manner in which
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