"Action of recti muscles"

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PDF from photocopy; Taubman Medical Library, University of Michigan.

[The PDF contains the letter to the Editor by Edward Lonsdale, published in LMG 23 (15 December 1838): 415-17; as well as Snow's reply, which is transcribed below. Lonsdale's letter has not been transcribed.]

To the Editor of the Medical Gazette

Sir,

I beg to offer some observations on the letter of Mr. Lonsdale, in the Medical Gazette of the 15th of this month, on the action of the recti muscles of the abdomen.--I remain, sir,

Your obedient servant,

John Snow, M.R.C.S.

54, Frith Street, Soho

Dec. 29, 1838.

As I am not about to espouse any of the opinions of previous authors, I shall only notice one or two of Mr. Lonsdale's criticisms of these opinions. He says that if different portions of the rectus muscle had separate contractions, there would then be an unequal pressure upon the abdominal viscera. Now this would not be the case for two reasons: first, because the contraction of any part of the muscle would have a tendency to approximate its two ends, and would consequently produce an equal tension throughout the whole length of the muscle; and, secondly, the abdominal viscera move with sufficient freedom on each other to be placed under the laws which govern fluids, consequently any pressure is felt equally through the whole of these viscera. He says also, in answer to Bertin's opinion, that if the blending of the tendinous intersec­tions of this muscle with its sheath were to enable it to assist more completely the action of the other abdominal muscles, these intersections would then be found adhering to the sheath at its posterior part also, for at present they would pull irregularly. Now Mr. Lonsdale must know that the anterior and posterior parts of the sheath of the rectus become intimately blended at the linea semilunaris, before reaching the muscular [559/560] fibres of the oblique; consequently any degree of traction exerted through the anterior part of the sheath would be as equally diffused as through both parts.

Mr. Lonsdale says, that when this muscle contracts, from being in a straight line, it takes on a curved direction backwards towards the spine; and this is not a mistake or a misprint, for it is a necessary part of the theory he advances, and it is exemplified by an engraving. Now for a muscle, extending in a straight line between two fixed points, to take on a curved form, it must become longer instead of contracting; and in the engraving it is actually figured much longer in its so-called contracted state than when relaxed. When the muscle becomes curved in the manner here described, it is not by its own contraction, but it is drawn into this form by the contraction of the transversus and part of the two obliqui muscles; if it contract when retained in this position, it will draw down the sternum and ribs, causing expiration, but still its tendency will be to assume a straight position. The rectus can only compress the abdominal viscera to the extent it does when it becomes a straight line between the pubes and sternum, after being curved forward; if it continue to contract after it has become straight, or when it is held forcibly in a curve, it will then approximate the sternum to the pelvis. The muscles that can retain it in the curved position backward are stated above; and the diaphragm, by pressing on the abdominal viscera, can curve it forward and retain it so.

I will not comment on Mr. Lonsdale's suggestion that the tendinous intersections give the muscle a greater power of contracting since he supports it only by saying, that the opposite cannot be proved.

I do not see any thing important in the absence of any adhesion between the rectus and the posterior part of its sheath. A muscle that has a separate and individual action, is, of necessity, never so connected with surrounding parts as to have its motions prevented. Between the tendinous intersections on its anterior part the muscle is merely united to its sheath by cellular tissue; and at its posterior part, where the tendinous intersections are scarcely seen, it is connected only by cellular tissue in its whole length.

But the structure even of this muscle does not admit of the application of Mr. Lonsdale's theory: it is not, as he states, composed of an anterior half with tendinous intersections and a posterior half without; but, agreeably to the de­scriptions of Boyer and Cloquet, the fibres arising from intersection are, for the most part, not inserted into the one immediately above, but dip behind it, and are inserted into a tendinous band higher up, so that few of the fibres of this muscle extend its whole length.

To conclude, I do not think these tendinous bands, which are found varying in number and situation in the rectus abdominis muscle, execute any important office; like the cicatrix on the skin which covers this muscle (the um­bilicus) and numerous other parts in the body, they are perhaps the remnant of some more early state of organization.