On the development of striated muscular fibre in Mammalia / by William S. Savory ; presented by James Paget.

  • Savory, William Scovell, 1826-1895.
Date:
[1855]
Catalogue details

Licence: Public Domain Mark

Credit: On the development of striated muscular fibre in Mammalia / by William S. Savory ; presented by James Paget. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    All the changes which have been described may often be traced in the same speci- men : first, the attachment of nuclei to the exterior of the fibre; secondly, their in- vestment by blastema; thirdly, the gradual sinking of the nuclei into the substance of the fibre, the corresponding subsidence of the elevation, the development of striae, &c. Authors generally describe and figure, after Valentin and Schwann, foetal fibres in which the nuclei in the interior are represented as bulging the fibres or prominent on the surface. I believe such descriptions and representations to have been drawn from fibres which were growing and developing by the addition of fresh nuclei, in the manner I have described. Foetal fibres rarely possess the same diameter throughout their entire length ; they are seldom uniform in this respect. Now this variation is easily explained by their mode of increase. Those portions to which fresh material has been recently added are for a time increased in diameter, but each inequality gradually disappears. It might be imagined that this condition is due to pressure, and undoubtedly this source of error is very liable to arise; but the variation may be constantly observed, even when the fibre floats freely in the field. Lastly, the substance of the fibre becomes contracted and condensed. The dia- meter of a muscular fibre from a foetus towards, or at the close of intra-uterine life, is considerably less than the diameter of a fibre at a much earlier period. As the fibre acquires its more perfect characters, so its substance becomes con- densed : it diminishes in size. This is continually counteracted to some extent, by the addition of fresh material and nuclei; but notwithstanding this, the size of the fibre continues for a time to decrease, so that the diameter of a muscular fibre at birth is considerably less than it was during a much earlier period of its existence *. That this decrease in the size of the fibre is due to a condensation of its substance, and not to stretching or any like cause, seems proved,— 1st, by the relative position of the nuclei, for the decrease in breadth is not accompanied by a corresponding sepa- ration of the nuclei; and 2ndlv, by the tact, that as the fibre decreases it becomes much less transparent. The nuclei in its interior grow much more obscure, and they are at length concealed by the increasing density of the muscular substance. At the time of birth muscular fibres present considerable variety in size and other characters. The great majority measure in the pig from -joVoth to -^ypjth of an inch in width, but many will be found beyond either of these extremes. The striae are very plainly marked, and in many almost as large as in the adult fibre; in some, however, they are much finer. In most of the fibres the nuclei in their interior are obscured or quite hidden by the density of their substance, but in others they are still * Thus, for example, taking average specimens:— Diameter of fibre of pig at time of birth, 3 Q'Q 0th of an inch. Diameter of fibre of pig 5 inches long, °f an inch. 2 M MDCCCLV.