516 MAMMALIA. 



two tubular uteruses open, without forming a vagina, on papilli- 

 form prominences into the urinogenital sinus, which is still con- 

 nected with the cloaca (Fig. 270). 



According to the different degrees of duplicity of the uterus 

 (when a vagina is present), we may distinguish : the uterus 

 duplex, with more or less complete external separation and 

 double OS uteri (rodents, marsupials) : the uterus bipartitus, with 

 single OS uteri, but almost complete internal partition (rodents) ; 

 the uterus bicornis (Fig. 270, b), in which the upper parts, or 

 horns of the uterus are separate (Ungulata, Carnivora, Cetacea, 

 Insectivora) ; and finally the uterus simplex (Fig. 270, c) with 

 single cavity and very muscular walls (Primates). 



The vestibule, with its glands of Duvernoy (Bartholin), which 

 correspond to the Cowperian glands of the male, is separated 

 from the vagina by a constriction, and in Homo also by a fold of 

 the mucous membrane, called the hymen. The external gener- 

 ative organs consist of the labia majora and labia minora, at the 

 sides of the sexual opening, and of the clitoris. The labia majora 

 are two external folds of skin, and are equivalent to the two 

 halves of the scrotum ; the labia minora are two smaller internal 

 folds, and are not always present. The clitoris possesses erectile 

 tissue and a glans, and is the equivalent of the penis. The 

 clitoris may sometimes (as in Aides) reach to a considerable size 

 and be perforated by the urethra (rodents, moles, lemurs). In 

 such cases of perforated clitoris, there is, of course, no common 

 urinogenital sinus. Morphologically, the female genitalia repre- 

 sent an earlier stage of development of the male organs, which, 

 in the cases of the so-called hermaphrodite formation., may in 

 consequence of arrest of development preserve a more or less 

 female stnicture. As a rule the two sexes are easily distin- 

 guished by the different form of the external generative organs. 

 Frequently there is a marked dimorphism in the whole external 

 appearance ; the male being larger, having a different hairy 

 covering, being possessed of a louder voice, and provided 

 with stronger teeth or special weapons (horns). On the 

 other hand, the milk glands, which are situate in the inguinal 

 region, on the abdomen, and on the thorax, and which almost 

 always project into teats or nipples, are rudimentary in the 

 male sex. 



There is in Mammalia a breeding period which may be called 



