UTERUS (FUNCTIONS). 



When labour is about to commence, the 

 uterus having previously taken a lower posi- 

 tion in the pelvis, begins to contract gently, 

 and often without pain, so that the only or 

 chief evidence of its action is an occasionally 

 recurring tension and hardness of the organ. 



These contractions commence apparently at 

 the cervix, so far as it is possible to analyse 

 them, and travel onwards towards the fun- 

 dus * : the whole organ soon becoming firm 

 and resisting to the touch, and its upper part 

 rising and assuming a more prominent posi- 

 tion in the abdomen. This hardness and 

 tension is occasioned partly by the rigidity of 

 the whole fibre, in a state of tonic contraction, 

 and partly by the resistance offered by the in- 

 compressible contents of the organ, for which 

 there is no exit so long as the cervix remains 

 closed. 



The contraction having overspread the 

 uterus, a sense of pain is now first felt ; the 

 pain, like that of cramp, being usually propor- 

 tionate to the sensible tension and hardness 

 of the organ. 



After enduring for a time the state of con- 

 traction gradually subsides, and is replaced 

 by one of relaxation. In subsiding, the con- 

 traction observes the same order as in com- 

 mencing, the os and cervix yielding first, while 

 the upper portion and fundus remain longest 

 tense and hard. From this it results that the 

 antagonistic force, exerted by the two ex- 

 tremities of the organ, not being throughout 

 contemporaneously and equally employed, the 

 excess of the fundal over the ostial contrac- 

 tion will represent the measure of the unop- 

 posed, and consequently efficient, propelling 

 power. 



The period of action is followed by one of 

 repose, in which the organ remains relaxed, 

 and no pain is experienced. 



After an interval of variable duration con- 

 traction returns, and continues to recur in 

 rythmical order, but with a gradually diminish- 

 ing interval, while at the same time the con- 

 tractions, especially at the fundus, increase in 

 intensity and duration. 



As a result of these successive contractions, 

 the os and cervix slowly yield, and a portion 

 of the foetal membranes, containing some 

 liquor amnii, protrudes, in the form of a 

 pouch. This, as the os uteri becomes still 

 further opened, is followed by the head or 

 some other portion of the child, which, having 

 entered the vagina, ultimately fills up the 

 pelvis, and distends the perineum. 



At this period the abdominal and pelvic 

 muscles are brought powerfully into play. 

 Their cooperative action is occasioned by the 

 parts of the child occupying the pelvis irri- 

 tating structures which are abundantly sup- 

 plied by spinal nerves. And now the chief 

 use of spinal reflex action, in relation to 



sideration in a separate article (PARTURITIOX, 

 MECHANISM OF, Vol. III. of this Cyclopaedia), the 

 vital endowments only of the uterus, as far as these 

 relate to the parturient act, are here examined. 

 * Wigand, Die Geburt des Menschen. Berl. 1820. 

 Supp. 



673 



labour, becomes manifest, not so much in 

 regard to the uterus itself, whose contractions 

 are probably still mainly dependent upon its 

 own sympathetic nerves, as in that correlation 

 with other parts, between which and the 

 uterus it is essential that consentaneous 

 action should be occasionally established. 



The powerful cooperation of the abdomi- 

 nal muscles, which form as it were an addi- 

 tional sheet of contractile fibre, nearly sur- 

 rounding the uterus, being thus enlisted, the 

 passage of the child is completed with greater 

 rapidity and certainty ; and, after a pause, 

 the placenta and membranes are expelled, the 

 liquor amnii having, either altogether or in 

 part, escaped at some earlier period of the 

 labour. 



This general sketch of the operations of 

 the uterus in labour will suffice as an intro- 

 duction to a more detailed and critical exami- 

 nation of the nature of the forces employed, 

 and of the manner in which these are called 

 forth. 



Of the peristaltic action of the uterus t and its 

 cause. From direct observation upon many 

 mammalia, it is known that the action of the 

 uterus is in them peristaltic, i.e., the contrac- 

 tions commence at certain points, and pass on 

 from segment to segment slowly, and in a ver- 

 micular manner. If a single point of an organ 

 so composed is irritated, the action starts from 

 the point of irritation, and spreads outwardly, 

 and by irritating different points, other peri- 

 staltic centres may be obtained. 



Although the human uterus does not admit 

 of the same direct methods of observation 

 w hich can be employed in animals, yet from 

 all that is known, we may conclude that its 

 mode of contraction does not differ in any 

 important particular from that of other simi- 

 larly constructed hollow muscles, when en- 

 gaged in propelling or expelling their contents. 



The principal circumstances bearing upon 

 this point in regard to the human uterus are 

 the gradual and slow contraction, followed by 

 an equally slow return to a state of relaxation 

 phenomena easily observed, when the hand 

 is placed upon the abdomen of a woman in 

 labour a certain tremulous motion of the os 

 uteri, when contraction is commencing, fol- 

 lowed by a sensible gradual hardening of the 

 uterus, before the woman is herself conscious 

 of pain ; the longer abiding of the contrac- 

 tion at the fundus than at the cervix ; and 

 the occasional segmental contraction of the 

 organ after labour, commonly termed hour- 

 glass contraction *, which may occur at any 

 point intermediate between the fundus and 

 cervix, and which resembles similar contrac- 

 tions of common occurrence in other hollow 

 muscles, whose action is peristaltic. These 

 several circumstances, added to the general 

 analogies, suffice to show that the action of 

 the human uterus is peristaltic. 



Peristaltic action, as it occurs in vertebrate 

 animals, is found to depend upon the struc- 

 ture of the organ displaying it, rather than 

 * See p. 702. 

 x x 



