THE HUMAN EMBRYO. 



with the abdominal openings, are widely separate ; their pos- 

 terior portions lie side by side, between and slightly dorsal to 

 the Wolffian ducts, and bound up with these by connective 

 tissue, to form what is spoken of as the genital cord. The 

 Miillerian ducts still end blindly behind. 



Towards the end of the third month, the two Miillerian ducts 

 fuse together, opposite the middle third of the genital cord ; and 

 from this point the fusion extends rather rapidly forwards, and 

 much more slowly backwards. The fused portion, or utero- 

 vaginal canal, enlarges steadily, especially in its transverse 

 diameter. By the beginning of the fourth month, a distinction 

 appears between the uterine and vaginal portions of the canal ; 

 the proximal portion, or uterus, being lined by a columnar epi- 

 thelium, and the distal portion, or vagina, by a squamous 

 epithelium. 



During the fourth month, the boundary line between the 

 uterus and vagina becomes a much sharper one. The uterus 

 becomes considerably dilated : the vagina, on the other hand, is 

 flattened dorso-ventrally ; and, by proliferation of its epithelial 

 cells, its lumen becomes completely blocked up for a time, re- 

 appearing in the course of the fifth month. 



The two Miillerian ducts thus give rise to the whole length 

 of the female passages ; the anterior or proximal ends of the 

 ducts remaining distinct from each other, and forming the 

 oviducts or Fallopian tubes ; while the posterior or distal por- 

 tions fuse together, and give rise to the uterus and vagina. 



The fusion of the two halves of the uterus is not completed 

 until the latter part of the fourth month ; and the occasional 

 retention of a more or less complete uterine septum, even in the 

 adult, is due to imperfect fusion of the two originally distinct 

 ducts. 



The cervix uteri is established during the fifth month, at 

 the time when the lumen of the vagina is reappearing. The 

 folds of the wall of the cervix, spoken of as the arbor vitee, 

 appear during the fourth month; while the differentiation of 

 the muscular walls, and of the enormously developed muscularis 

 mucosaB commences in the sixth month. The uterine epithelium 

 is devoid of cilia during the whole of foetal life ; and up to the 

 time of birth there are no glands in the body of the uterus. 

 Glands are, however, present in the cervix, and apparently 



