THE UTERUS. 201 1 



For a time this tube ends blindly and is continued to the urogenital sinus, with which 

 it unites, as a solid cylinder of larger cells ; this lumenless segment of the fused 

 Miillerian ducts represents the anlage of the vagina. The extent to which the 

 Miillerian ducts undergo fusion is early indicated by a sharp inward bend of these 

 tubes just below the lower and medial ends of the Wolffian bodies, the flexure on 

 each side corresponding to the attachment of fibres that pass to the anterior abdom- 

 inal wall and later from the round ligament. The portions of the Miillerian ducts 

 above this point remain separate and ununited and become the oviducts, those below 

 undergo fusion and produce the uterus and vagina. 



After the vaginal portion of the united Miillerian ducts acquires a lumen (by 

 the end of the fourth month), the uterine and vaginal segments of the tube are dif- 

 ferentiated by the tall cylindrical and the larger cuboidal epithelial cells that line 

 the two portions respectively. The transition zone, which becomes progressively 

 more marked, corresponds to the position where later the cylindrical uterine epithe- 

 lium changes into the squamous vaginal cells at the inner margin of the external os. 

 Soon the distinction between the uterine and vaginal portions of the genital canal is 

 additionally emphasized by the forward curve of the former and the straighter 

 downward course of the latter. The more definite division of the uterus from the 

 vagina is effected by the appearance of crescentic thickenings of the anterior and 

 posterior walls of the canal which mark the beginnings of the corresponding lips of 

 the cervix. Distinction between the body and cervix is early suggested by the 

 uterine epithelium, the cells lining the lower portion being taller, more cylindrical 

 and numerous than those of the body. The connective and muscular tissue of the 

 uterine wall are differentiated from the condensed mesoderm that surrounds the 

 epithelial tube. Distinct muscle is not distinguishable before the fifth month, about 

 which time the cervical glands also make their appearance (Nagel), thus anticipa- 

 ting by some weeks the development of the glands in the corpus uteri. 



At birth the uterus measures about 3 cm. in length, of which the cervix con- 

 tributes more than half, and is thicker and denser than the thin-walled and flaccid 

 body. The characteristic arched form of the fundus is lacking and the lateral 

 angles are prolonged into the tubes, often recalling a bicornate condition. The 

 portio vaginalis is inconspicuous and projects to only a slight degree, although the 

 plicae palmatae are well developed and not limited, as they later are, to the cervical 

 canal, but extend throughout the uterine cavity. Since at this time the internal os is 

 still immature, the division of the uterine cavity into an upper and a lower segment 

 is only suggested. The general position of the uterus is higher than later, it, 

 together with the bladder, lying above the level of the pelvic brim, with the fundus 

 opposite about the fifth lumbar vertebra (Merkel). With the increasing capacity of 

 the pelvis, the uterus sinks, so that by the end of the sixth year the external os is 

 little higher than in the adult (Symington). Apart from the gradual development 

 of the glands and the disappearance of the folds of the mucosa within the body, 

 during childhood the uterus grows slowly until near puberty, when the body 

 thickens, lengthens, and acquires the arched contours of its mature form. In its 

 relatively long cervix and slightly prominent fundus, the uterus of the virgin retains 

 the characteristics of early childhood. The repeated changes incident to the men- 

 strual cycle, produce gradual thickening of the uterine walls and enlargement of the 

 lumen, so that, even independently of pregnancy, the uterus increases somewhat in 

 size and weight during the years of sexual activity. 



After the cessation of menstruation, between the forty-fifth and fiftieth years, 

 the uterus suffers gradual atrophy (involution). This first affects the cervix, which 

 becomes smaller and more slender, the entire organ in consequence assuming a 

 more pronounced pyriform outline. The general reduction in the size and prom- 

 inence of the vaginal portion is accompanied by atrophy of the plicae palmatae of the 

 cervical canal. The walls of the body are also involved and become thinner and 

 less resistant with atrophy of the muscular tissue and decreased vascularity, and 

 hence paler color, of the mucosa. For a time the uterine cavity is enlarged, but, 

 later, sharing in the general atrophy and not inconsiderable diminution in size of the 

 organ, the lumen likewise undergoes reduction and, in some cases, suffers obliteration 

 in the vicinity of the internal os. 



