. An American text-book of obstetrics. For practitioners and students. ofthe os. To these considerations must be added the effect of the peculiar compositionof the uterine muscle and of the peculiar character of its contractions. It isessential to remember that this highly composite muscle is made up of inter-lacing fibres, whose action may mechanically be divided into one set oflongitudinal and one of circular stresses; that is, if the action of those fibreshaving an oblique direction be resolved, as is physically allowable and proper,into their longitudinal and transverse resultants, the act
. An American text-book of obstetrics. For practitioners and students. ofthe os. To these considerations must be added the effect of the peculiar compositionof the uterine muscle and of the peculiar character of its contractions. It isessential to remember that this highly composite muscle is made up of inter-lacing fibres, whose action may mechanically be divided into one set oflongitudinal and one of circular stresses; that is, if the action of those fibreshaving an oblique direction be resolved, as is physically allowable and proper,into their longitudinal and transverse resultants, the action of the whole willbe found precisely equal to that which would be exerted by two hypotheticalsets of fibres, of which the first and most powerful set directly encircle the ute-rus in horizontal zones, while the second and less powerful set extend upwardthrough the margin of the os, cross the fundus, and thence passing down toreach the margins of the os at points opposite to their origins. If a uterine muscle so composed were set into action, it will be seen that,. Fig. 236.—Diagrams showing the diminutionof the upper uterine segment and the expansionof the lower segment during each contraction. 426 AMERICAN TEXT-BOOK OE OBSTETRICS. from a mechanical standpoint, the circular fibres surrounding the os would bytheir contraction tend to keep it closed, while the longitudinal fibres, acting inopposition to these, would by their contraction tend to open the os by drawingits margins apart over the contained ovum. This conception, though some-what more simple than the actual anatomical fact, is mechanically essentiallycorrect; but, since the circular stresses are the more powerful, it is evidentthat this arrangement cannot result in the dilatation of the os unless compli-cated by the presence of some additional factor. This factor is found in thecircumstance that the contractions of the uterine muscles, like those of all thehollow viscera of the body, are peristaltic, and that the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
