908 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



gestation is of longer duration. Thus, the water-rat or guinea-pig may 

 bear five or six times a year. 



In most mammals the uterus is not constituted by a single cavity, 

 as in the human female, but is prolonged more or less on each side, con- 

 stituting what are termed the horns of the uterus. Sometimes, as in car- 

 nivora, the division of the uterus is prolonged up to the vaginal orifice 

 of the uterus. This division of the uterus into two horns, or two pouches, 

 more or less distinct, does not occasion any difference in the mode of 

 connection of the eggs with the uterine mucous membrane. In the 

 carnivora and in rodents the mucous membrane, as in the human species, 

 adheres to the body of the organ and separation is extremely difficult.. 

 In solipedes and the pachyderms the uterine mucous membrane is but 

 slightly adherent to the subjacent tissue and may even be thrown into 

 folds. 



In horned ruminants, as the cow, the mode of union of the egg 

 with the uterine mucous membrane presents a remarkable peculiarity. 

 The foetal placenta occurs in isolated cotyledons, the cotyledons being- 

 formed, as in the human species, of vascular loops implanted in the 

 mucous membrane of the uterus, being designated under the name of the 

 uterine cotyledons. These uterine cotyledons exist in the female even 

 before pregnancy and persist after the separation of the foetus and its 

 multiple placenta. 



When the young of a mammal is born the membranes of the egg and 

 the umbilical cord frequently rupture spontaneously. In other cases the 

 female breaks the membranes and the cord with her teeth. Most car- 

 nivorous animals devour the after-birth. In the horned ruminants the 

 adhesion of the cotyledons of the fcetal placenta with the uterine coty- 

 ledons is so close that frequently several days elapse after the birth of 

 the foetus before the placenta becomes detached. In such animals the 

 expulsion of the placenta cannot be facilitated by drawing on the umbili- 

 cal cord without great risk of hemorrhage from rupture of the uterine 

 vessels. 



When the animal is multiparous the membranes and placenta of each 

 are expelled with the young to which they belong. In certain species of 

 mammals the young are but slightly developed and are incapable of 

 making use of their limbs. Many such animals, as the marsupials, 

 remain permanently attached to the breasts of the mother while carried 

 in pouches formed by a fold of the integument of the abdomen. 



1. The Reproductive Tissues of the Female. — As already stated, 

 reproduction is dependent upon the union of the ovum contributed by 

 the female with the spermatozoa formed by the sexual organs of the 

 male. These reproductive tissues in mammals now deserve somewhat 

 further attention. Nothing need be added to the morphological clescrip- 



