THE VAGINA. 1321 



mucous membrane disintegrate and haemorrhage takes place from the small super- 

 ficial blood-vessels. In this way a hsemorrhagic discharge is caused, and the 

 superficial parts of the uterine mucous membrane are shed at each period. When 

 menstruation is over the mucous membrane is rapidly regenerated. 



Pregnant Uterus. The pregnant uterus increases rapidly in size and weight, 

 so that from being three inches in length and one ounce in weight, it becomes by 

 the eighth month about seven or eight inches in length and sometimes as much 

 as two pounds in weight. In shape the uterus is now oval or rounded, with a thick 

 wall composed chiefly of muscle fibres arranged in distinct layers. The rounded 

 fundus is very prominent. The round ligaments are stronger and better marked, 

 and the layers of the broad ligament become separated in their medial parts by the 

 growth of the uterus between them. The blood-vessels, especially the arteries, are 

 very large and tortuous. The changes which occur in the mucous membrane of 

 the pregnant uterus are intimately connected with the manner in which the 

 developing foetus receives its nutrition, and have been noticed on pp. 56 et seq. 



Vessels and Nerves of the Uterus. The uterus receives its arterial supply mainly from 

 the uterine arteries, which are branches of the hypogastric arteries, and also from the ovarian 

 arteries, branches of the aorta. The vessels derived from these two sources communicate freely 

 with one another. Each uterine artery, reaching the side of the lower part of the uterus, divides 

 into a large branch which passes upwards to supply the body and fundus, and a much smaller 

 branch which passes downwards to supply the cervix. The vessels distributed to the body and 

 fundus have an exceedingly tortuous course. The branches of the uterine artery, having entered 

 the muscular coat, break up within its deeper layers into smaller twigs which supply the muscular 

 tissue and the mucous coat. The small uterine branch from the ovarian artery reaches the 

 uterus in the region of the lateral angle. During pregnancy the arteries become enormously 

 enlarged. 



The thin-walled veins form a plexus which pours its blood into the tributaries of the hypo- 

 gastric vein. 



The nerves of the uterus are derived chiefly from a plexus placed in the neighbourhood of 

 the cervix uteri, to which the term plexus uterovaginalis or " cervical ganglion " is applied. 

 Superiorly this plexus is continuous with the hypogastric plexus, but it also receives fibres from 

 the third and fourth sacral nerves. In addition to fibres from the plexus uterovaginalis, the 

 uterus receives fibres directly from the hypogastric plexus, and also from the plexus vesicalis. 



Clinical observations indicate that afferent impulses reach the central nervous system from the 

 uterus through the posterior roots of the tenth, eleventh, and twelfth thoracic nerves, the first 

 lumbar, and the second, third, and fourth sacral nerves. 



The numerous lymph-vessels coming from the body of the uterus join those from the ovary, 

 and end for the most part in the lumbar lymph -glands. Along the course of the round 

 ligament of the uterus there are a few lymph-vessels which establish a connexion between 

 the lymph -network surrounding the uterus and the inguinal lymph - glands. The lymph - 

 vessels from the cervix uteri end in the gland placed near the bifurcation of the common 

 iliac artery. 



VAGINA. 



The vagina is a passage about three inches in length, open at its lower 

 end, and communicating above with the cavity of the uterus. The passage is 

 directed downwards and forwards, describing a slight curve which is convex back- 

 wards. The axis of the vagina forms with that of the uterus an angle which is open 

 forwards. This angle is usually somewhat greater than a right angle, but varies 

 with the condition of the neighbouring viscera (p. 1319). The vagina is widest at 

 its upper end (Fig. 1034), and normally its anterior wall and its posterior wall 

 are in contact. In transverse section the lower part is usually an H -shaped cleft, 

 the middle part a simple transverse slit, while the lumen of the upper portion, into 

 which the cervix uteri projects, is more open. The lower part of the cervix uteri has 

 the appearance of entering the vagina through the upper portion of its anterior 

 wall (Fig. 1033). As more of the posterior than of the anterior part of the cervix 

 projects into the vagina, a deeper recess is formed between the vaginal wall and 

 the cervix behind than in front or laterally. The term anterior fornix is often 

 applied to the angle, or recess, in front ; posterior fornix to the deeper angle behind, 

 and lateral fornix to the recess on each side of the cervix uteri, between it and the 

 wall of the vagina. The anterior wall of the vagina (paries anterior) is shorter 

 than the posterior (paries posterior), the former being about three inches in length, 



