1538 PARTURITION. [BOOK iv. 



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. 



968. The nerves of the uterus reach that organ chiefly 

 along the broad 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 ; 

 it will be remembered that a like difference has been stated to 

 obtain in the case of the rectum ( 276). Moreover, while the 

 fibres passing by the hypogastric nerve are vaso-constrictor towards 

 the uterine arteries, it is said that those passing by the sacral 

 nerves are vaso-dilator. It would be hazardous at present however 

 to insist on any sharp distinction between the two sets of fibres as 

 to the kind of muscular contraction which they bring about ; 

 and we may conclude that when the lumbar centre, excited in a 

 reflex action, sends out efferent impulses, these, whatever be their 

 exact nature, pass along both sets of fibres to the uterine muscles. 



969. Though we may speak of even the distinctly uterine 

 portion of the act of parturition as reflex in nature, we are hardly 

 justified in considering the rhythmical contractions of the uterus 

 during parturition as simple reflex acts exactly comparable to the 

 contractions of the skeletal muscles in an ordinary reflex move- 

 ment of the limbs. The peculiar rhythmic character of the 

 contractions, each ' pain ' beginning feebly, rising to a maximum, 

 then declining, and finally dying away altogether, to be succeeded 

 after a pause by a similar pain just like itself, pain following pain 

 like the tardy long-drawn beats of a slowly beating heart, suggests 

 that the cause of the rhythmic contraction is seated, like that of 

 the rhythmic beat of the heart, in the organ itself. And this 

 view is supported by the fact that contractions of the uterus, 

 similar to those of parturition, have been observed in animals 

 even after complete destruction of the spinal cord ; in such cases 



