14 INTERNAL SECRETIONS OF THE OVARY 



The uterus. The Fallopian tubes open into the uterus, which 

 consists essentially of the same three layers, but the internal 

 mucous membrane is much thickened to form the uterine 

 mucosa (or endometrium) which consists of a glandular stroma 

 lined by epithelium. The shape of the uterus shows great 

 specific variation. At one extreme is the type having two 

 distinct cornua fusing only at the junction with the vagina, and 

 even there retaining two distinct cervical canals. This type of 

 uterus is characteristic of the rat and the mouse. At the other 

 extreme is the type where the cornua are entirely fused to form 

 one large (usually pear-shaped) uterine sack, into the top angles 

 of which open the two Fallopian tubes. This type is 

 characteristic of the human. Between these extremes every 

 gradation is found, from the rabbit, where the cornua are fused 

 to the extent of having a common cervical canal, to the goat 

 where fusion is complete except for the tops of the cornua, 

 which form two horns projecting from the main body of the 

 uterus. 



The vagina. The vagina, which connects the uterus with 

 the exterior, possesses the two muscular layers found in the 

 other sections of the genital tract, and is lined internally with 

 epithelium, the nature of which varies greatly in different 

 animals and in different stages of the cestrous cycle. In man 

 erectile tissue is present, but this appears to be absent in the 

 lower species, in which the necessary facilitation to copulation 

 is obtained by copious secretion (cow), intense hyperaemia 

 (ferret) or cornification (mouse). The vagina opens to the 

 exterior at the vulva, the anatomy of which varies greatly 

 in different species, being a simple orifice in the case of most 

 lower mammals, and complicated in the human by inner 

 and outer labia. 



In the rat and mouse the vaginal lumen is not complete during 

 pre-pubertal life. In the foetus the cord of cells destined to 

 form the vagina first shows a lumen at the anterior end. This 

 lumen extends until it is separated from the exterior only by a 

 thin wall of cells, which remains in the rat and mouse until 

 the first oestrous period, when it is ruptured by the enlargement 

 of the vagina. The closure of the immature rodent vagina may 

 be analogous to the partial closure of the human vagina effected 



