•92 OBSTETRICAL PHYSIOLOGY. 



shed or disappears in some obscure manner, and the caruncle again 

 assvimes its smooth surface. 



As in SoHpeds, there is no direct vascular communication between 

 the maternal and foetal cotyledons, the villi of each being distinct, 

 though in close contact, being only separated at points by the lactescent 

 fluid just alluded to. This fluid, which is present in all the domesti- 

 cated animals, can be readily discovered by carefully withdrawing a 

 ■ chorionic tuft from the alveolar cavities of the uterine cotyledon. 



Sheep and Goat. 

 In the Sheep and Goat the arrangement of the placenta is essentially 

 the same as in the Cow, except that the maternal cotyledons are deeply 

 concave or cup-shaped in the middle, and into this cavity the fcEtal 

 placentula is received and closely retained. This placentula is not so 

 wide as that of the Cow, though it is thicker and the villi are more 

 delicate. The mode of termination of the placental vessels in the 

 Sheep is villous ; in the Goat it is pilose. 



Pig. 

 In the Pig the placenta may be designated as " diffused," not " poly- 

 cotyledonary " as in Euminants ; though the tufts do not form a con- 

 tinuous layer, as in the Mare, the papillas being collected in small but 

 closely-grouped clusters. When uninjected they appear as white 

 masses or spots scattered over the external surface of the chorion, thus 

 giving it a mottled aspect, caused by the presence of feebly vascular and 

 non-vascular areas ; but when the allantoic veins are filled, these are 

 seen to form plexuses in the centre of each spot. The uterine veins 

 have a cori'esponding arrangement, and the arterial capillaries form a 

 fine network, the meshes receiving the villosities which carry the fcetal 

 arterial capillaries ; whence it might seem that the nutrition of the 

 foetus is effected principally at the points of contact of the foetal with 

 the maternal venules, while the respiratory process took place at the 

 surface of contact between the foetal and maternal arterial capillaries. 

 The chorion is destitute of these papillae at its extremities, which are in 

 contact with the chorion of other foetuses in the uterus. 



Bitcli and Cat. 



In the Bitch and Cat the placenta forms a thick annular band or 

 zone, about one or one and a half inch wide, passing round the middle 

 of the chorion ; it is therefore said to be " zonular." This zone is con- 

 cave within, of a mixed grey-and-red colour when uninjected, livid or 

 dark brown during gestation ; its foetal surface is lobulated, and the 

 zone is limited at each side by a dark green border, the colouring matter 

 of which can scarcely be removed by repeated washings. 



The placenta is studded with ramified villi of a leaf or plate shape, 

 which are implanted in the uterine mucous follicles. The mucous 

 membrane in which these are situated, and w^hich corresponds to the 

 placenta, presents a kind of vascular fungous development that appears 

 after parturition, but which at an early stage of pregnancy has a 

 quantity of fluid along its margin; the maternal placenta, or scrotina 

 decidua, is present during gestation, and can be separated as a distinct 

 layer. There cannot be a doubt that the uterine mucous membrane in 

 Carnivora secretes a kind of plastic lymph, which forms this caducous 

 lining, or membrana decidua ; but it is only present at a certain period 

 ■ of fcEtal life, and forms the base of the uterine placenta. 



