THE VAGINA. 259 



swollen, excessively vascular and hypertrophied, with conspicuous enlargement of 

 the subepithelial blood-vessels and the glands. The resulting thickened and modified 

 mucosa, now from 6-7 mm. thick, offers a soft velvety surface favorable for the 

 implantation of the embryo-sac. Should this occur, the hypertrophy proceeds, and 

 the lining of the uterus is converted into the deciduai and takes an important part in 

 the formation of the placenta. If, on the contrary, fertilization does not occur, the 

 proliferative processes are arrested and the hypertrophied mucosa, now called the 

 deddua menstrualis, enters upon regression. Incidental to the latter are subepithelial 

 extravasation and rupture and partial destruction of the epithelium, followed by the 

 characteristic discharge of blood. While usually the destruction of the mucosa is 

 limited to the epithelium, it is probable that at times the superficial layer of the sub- 

 jacent tissue is involved. 



During pregnancy the most conspicuous changes are occasioned by the growth 

 necessary to accommodate the rapidly augmenting volume of the uterine contents, by 

 the provision of an adequate source of nutrition and protection for the foetus, and by 

 the development of an efficient contractile apparatus for the expulsion of the same. 

 The enormous increase depends especially upon the hypertrophy of the muscular 

 coat, which during the first half of pregnancy becomes greatly thickened, but later 

 thinner and membranous owing to stretching. The increase results from both the 

 growth of the previously existing muscle-cells and, during the first half of pregnancy, 

 the development of new muscle elements. The individual cells may increase tenfold 

 in length and measure between -4-.5 mm. During the first five months, the mucous mem- 

 brane of the body also becomes greatly hypertrophied, in places attaining a thickness 

 from 7-10 mm. The glands and blood-vessels, particularly the arteries, enlarge and, 

 within the specialized area, are concerned in the formation of the placenta. The 

 cervical mucosa takes no direct part in the formation of the deciduae, although it 

 thickens and is the seat of enlarged glands that secrete the plug of mucus that for a 

 time occludes the mouth of the uterus. After the termination of pregnancy, the 

 uterus enters upon a period of involution and repair, the excessive muscular tissue 

 undergoing degeneration and absorption and the lacerated mucosa regeneration, the 

 latter process being completed in from three to four weeks. 



THE VAGINA. 



The vagina is a flattened muscular tube, lined with mucous membrane, 

 that extends from the genital cleft enclosed by the labia below to the uterus 

 above. Its walls, from 2-3 mm. thick, include a mucous and a muscular 

 coat, supplemented externally by a less definite fibrous tunic. 



The mucous coat consists of stratified squamous epithelium and a 

 fibre-elastic tunica propria, exceptionally rich in veins and colorless blood- 

 cells and beset with numerous conical papillae that encroach upon the 

 overlying epithelium, but do not model the free surface. Although nor- 

 mallyjmoistened by a thin mucous secretion of acid reaction, the vagina is 

 devoid of glands. Small lymph-nodules are scattered through the mucosa, 

 especially in the upper part of the canal. The hymen, the membranous fold 

 partly occluding the vaginal orifice, consists of a basis of vascular fibrous 

 tissue covered by a prolongation of the mucous membrane. 



The muscular coat, which supports the mucous membrane without 

 the intervention of a distinct submucous layer, is composed of bundles of 

 unstriped muscle arranged, although not with precision, as an inner circular 

 and an outer longitudinal layer. The latter is best developed over the 

 anterior vaginal wall, from which strands of muscular tissue are continued 

 into the urethro-vaginal septum. Behind, bundles are prolonged into the 

 recto-vaginal partition; above, the vaginal muscle is continuous with that of 

 the uterus and below penetrates the perineal body. Within the conspicuous 

 elevations, the columns rug arum, marking the vaginal wall, both mucous and 



