20I2 HUMAN ANATOMY. 



Changes during Menstruation and Pregnancy. — Although Hberation of a mature ovum 

 may occur at any time, such independence is exceptional, and in the vast majority of cases 

 ovulation and menstruation are synchronous processes, the uterine changes occurring regularly, 

 every twenty-eight days, only when the ovaries are functionally active. In anticipation of the 

 possible reception of a fertilized ovum, the uterine mucous membrane becomes swollen, exces- 

 sively vascular and hypertrophied, with conspicuous enlargement of the subepithelial blood- 

 vessels and the glands. The resulting thickened and modified mucosa, now from 3-6 mm. 

 :n thickness, offers a soft velvety surface favorable for the implantation of the embryo-sac. 

 bhould this purpose be realized, the hypertrophy proceeds, and the lining of the uterus is con- 

 verted into the decidute and takes an important part in the formation of the placenta and at- 

 tached membranes (page 44). If, on the contrary, fertilization does not occur, the proliferative 

 processes are arrested and the hypertrophied mucosa (now called the decidiia mensirualis) 

 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 subjacent 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. From an organ ordinarily weighing about 

 45 grams (i>^ oz. ), measuring 7 cm. in length and possessing a capacity of from 3-5 cc, by the 

 close of pregnancy the uterus has expanded into a rounded or oval sac about 36 cm. (14 in.) in 

 its greatest length, from 900-1000 grm. (about 2 lbs.) in weight and with a capacity of 5000 cc. 

 (169 fl. oz. ) or more. This enormous increase depends especially upon the hypertrophy of the 

 muscular coat of the organ, which during the first half of pregnancy becomes greatly thickened, 

 but later thinner and membranous owing to stretching. The increase in this coat 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. Although the cervix actually almost doubles in size, its growth 

 is overshadowed by that of the body, since it remains relatively passive. During the first five 

 months, the mucous membrane of the body of the uterus 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 

 (page 48). The cervical mucosa takes no direct part in the formation of the deciduce, 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 five to six weeks (Minot). In 

 sympathy with the growth of the myometrium, the round ligaments enlarge and also show marked 

 augmentation of their muscular tissue. The peritoneal relations are disturbed by the excessive 

 bulk of the uterus, so that at the sides the layers of the broad ligament become separated. 



Variations. — The chief anomalous conditions of the uterus depend upon defective devel- 

 opment or imperfect fusion of the Miillerian ducts by the union of which the normal organ is 

 formed. Arrested development of the lower part of these foetal canals accounts for entire ab- 

 sence of the uterus and vagina. Depending upon the extent to which failure of fusion occurs, 

 all degrees of doubling are produced. In the most pronounced cases, in which the Miillerian 

 ducts remain separate throughout their entire length, two completely distinct uteri and vaginae 

 may result, each pair being capable of performing the functions of the normal organs. On the 

 other hand, slight indentation of the fundus may be the only evidence of imperfect union. Be- 

 tween these extremes all gradations occur ; the body may be completely cleft {uterus bicornis), 

 with or without divided cervix ; or the duplicity may be partial and limited to branching of the 

 fundus ; or the faulty fusion may be manifested by only a partition, more or less complete, that 

 divides the uterine cavity into two compartments {uterus septus), although the external form of 

 the organ is almost or quite normal. When, in conjunction with any of the foregoing variations, 

 one of the component Miillerian ducts fails to keep pace in its growth, all degrees of asymmet- 

 rical development may result, from complete suppression of one of the tubes in a bicornate uterus 

 to merely unilateral diminution of the fundus. Subsequent arrest of what to a certain stage was 

 a normal development may result in permanent retention of the fcetal or infantile type of uterus. 



PRACTICAL CONSIDERATIONS : UTERUS AND ITS ATTACHMENTS. 



In the female the pelvis is subdivided into two compartments by a fold of peri- 

 toneum reflected from the floor and sides of the cavity. This fold passes from one 

 side to the other and includes between its layers in the median line the uterus. On 

 each side of the uterus it is knovv^n as the broad ligament, and encloses the uterine 



