THE UTERUS, OR WOMB 1411 



is made raw, so that if an impregnated ovum arrives it will adhere. Reichert believes that 

 menstruation means that no impregnated ovum has arrived in the womb, and hence no bed is 

 needed for one 



Changes Induced by Pregnancy. The muscle fibres hypertrophy enormously and be- 

 come vastly longer and broader. There is a great increase in connective tissue, and new 

 connective-tissue fibres pass between bundles of muscle. The peritoneal coat undergoes hyper- 

 plasia. It remains closely adherent to the uterus, except over the lower segment, from which 

 region it can be easily stripped. The bloodvessels become large and tortuous. The nerves are 

 increased in length and new filaments form. The lymphatics undergo hypertrophy and hyper- 

 plasia. The uterus becomes spherical, and after the fourth month ovoidal. Early in pregnancy 

 the increase in weight causes the uterus to descend in the pelvis. After the third month it rises 

 progressively, and during the ninth month the fundus reaches the epigastrium. "Before term 

 (four weeks in primiparse, ten days or one week in multipane) the fundus sinks again, as the 

 presenting part and lower uierine segment become engaged in the pelvic cavity. This phenome- 

 non is explained by contraction of the overstretched abdominal walls." 1 The womb is acutely 

 anteflexed during the first three months of pregnancy. After this period, as the womb rises, 

 the anteflexion is diminished, but some degree remains, because the abdominal walls are too lax 

 to hold the organ straight. The uterus passes somewhat to the right side and undergoes a rota- 

 tion on its longitudinal axis, so that the anterior surface looks front and to the right. These 

 changes in position are caused by fecal distention of the sigmoid. The intestines are above and 

 back of the uterus. During the first four months the cervix softens and enlarges somewhat. 

 The length of the cervical canal is not altered during pregnancy, and the canal does not dilate 

 until labor begins. During pregnancy the cervical glands secrete thick mucus, which coagulates 

 and occludes the cervical canal; the round ligaments become stronger, and the layers of the 

 broad ligaments are separated toward their inner portions by the enlarging womb. 



After parturition the uterus nearly regains its former size, usually weighing something over 

 one and a half ounces; but its cavity is larger than in the virgin state, the external orifice is more 

 marked, its edges present a fissured surface, its vessels are very tortuous, and its muscle layers 

 are more defined. 



Structure. The uterus is composed of three coats an external or serous coat, a middle 

 or muscular coat, and an internal or mucous coat. 



The serous coat or perimetrium (tunica serosa) is derived from the peritoneum; it invests 

 the fundus and the whole of the posterior surface of the uterus; but covers the anterior surface 

 only as far as the junction of the body and cervix. In the lower fourth of the posterior surface 

 the peritoneum, though covering the uterus, is not closely connected with it, being separated 

 from it by a layer of loose cellular tissue and some large veins. At the lateral margins of the 

 uterus the serous coat passes on to the broad ligaments. The serous coat adheres closely to the 

 uterus, and it is very difficult to separate it from the muscle. 



The muscular coat (tunica musculans} (Fig. 1164) forms the chief bulk of the substance of the 

 uterus. In the unimpregnated state it is dense, firm, of a grayish color, and cuts almost like 

 cartilage. It is thick opposite the middle of the body and fundus, and thin at the orifices of the 

 Fallopian tubes. It consists of bundles of unstriped muscle tissue, disposed in layers, intermixed 

 with areolar tissue, bloodvessels, lymphatic vessels, and nerves. The muscle tissue is disposed 

 in three layers external, middle, and internal. 



The external layer is placed beneath the peritoneum, disposed as a thin plane on the anterior 

 and posterior surfaces. It consists of fibres which pass transversely across the fundus, and, con- 

 verging at each superior angle of the uterus, are continued on the Fallopian tube, the round 

 ligament, the ligament of the ovary; some passing at each side of the broad ligament, and others 

 running backward from the cervix into the sacrouterine ligaments. The fibres of the external 

 portion of the outer layer (stratum subserosum) are longitudinal. The fibres of the inner portion 

 of the outer layer (stratum supravascnlare) are partly circular and partly longitudinal. 



The middle layer of fibres (stratum vascularc], which is thickest, presents bundles of circular 

 fibres closely connected with bloodvessels. In this layer are most of the large bloodvessels. 

 The circular fibres about the internal os form a distinct sphincter. Those which surround the 

 orifices of the Fallopian tubes are arranged in the form of two hollow cones, the apices of which 

 surround the orifices of the Fallopian tubes, their bases intermingling with one another on the 

 middle of the body of the uterus. 



The internal or deep layer (stratum mucomm) consists of longitudinal fibres. Some consider 

 the deeper portion of the muscle tissue of the uterus to be the muscularis mucosae. But the deep 

 portion of the muscle substance is continuous with the more superficial portion, and there is no 

 submucous coat between the muscle and the mucous membrane. The deeper layer of muscle 

 fibres of the uterus contains connective tissue and elastic fibres. The muscle tissue of the 

 cervix contains more connective and elastic tissue than does the body of the uterus; hence, the 

 cervix is harder and stiffer than the body. 



i A Text-book of Obstetrics. By Prof. Barton Cooke Hirst. 



