CHAP, ii.] PREGNANCY AND BIRTH. 1141 



produce their effect chiefly at least through their action on the 

 nervous centre. The ready way in which the uterus enlarged 

 by pregnancy responds by reflex contraction to the stimulation 

 of various afferent nerves is illustrated in the human subject 

 by the means usually adopted to secure after the birth of 

 the child that continued contraction by which hsemorrhage is 

 avoided. Should for any reason such a contraction fail to take 

 place, it may be secured by applying cold or pressure to the 

 abdominal walls or by introducing a hand or some foreign body 

 into the vagina, or, what perhaps best illustrates the reflex 

 nature of the matter, by applying the child to the nipple ; in 

 the latter case the relatively feeble afferent impulses generated 

 in the mammary nerves by the sucking of the child are especially 

 potent in producing by reflex action contraction of the uterine 

 muscles. 



709. The nerves of the uterus reach that organ chiefly 

 along the broiad ligament in company with the blood vessels, 

 are partly medullated, partly non-medullated, and are derived 

 from the pelvic plexus lying between the rectum and the 

 vagina. The pelvic plexus, on which as also on the nerves 

 passing to the uterus, numerous small ganglia are scattered, is 

 a continuation on each side of the body of the medially placed 

 hypogastric plexus, but it is joined by branches coming directly 

 from the sacral nerves. In the lower animals (dog) the roots 

 which supply fibres- to the uterus are on the one hand the upper 

 lumbar, which traverse the sympathetic strand known as the 

 hypogastric nerve, and on the other hand probably the first and 

 second sacral. In the human subject the corresponding roots are 

 probably the upper lumbar and third, fourth and second sacral. 



Stimulation, in the dog, either of the hypogastric nerve or of 

 the sacral nerves produces contractions in the pregnant uterus ; 

 it is stated that the mode of contraction is different in the two 

 cases, in the latter the longitudinally disposed fibres, in the 

 former the circularly disposed fibres being especially thrown 

 into action. Moreover, it is said that while the fibres passing 

 by the hypogastric nerve are vaso-constrictor towards the 

 uterine arteries, those passing by the sacral nerves are vaso- 

 dilator. Other observers have failed to obtain any such differ- 

 ence between circular and longitudinal contractions, and find 

 that in some animals at least, while contractions of the uterus 

 may be readily brought about by stimulation of the sympathetic 

 nerves from the lumbar region, passing through the hypogastric 

 nerves, contractions cannot with certainty be obtained by stim- 

 ulating the sacral nerves. On the other hand, stimulation of 

 the sacral nerves, of the second, third, and sometimes of the 

 first, readily produces movements of the vagina. It may be 

 added that stimulation of certain areas of the cerebral cortex 

 will give rise to movements of the uterus and of the vagina. 



