VIVIPAROUS ANIMALS. 403 



fluid exhibits very different properties, according to the 

 species from which it is obtained. The skin of the foetus 

 is frequently covered with a fatty matter, which some con- 

 sider as a deposition from the liquor amnii, but which 

 others, with greater propriety, regard as a cutaneous se- 

 cretion. Indeed, suspicions have arisen that the liquor it- 

 self is secreted by the foetus ; and these are countenanced 

 by the circumstance, that, in the amnios of some species, as 

 man, no bloodvessels can be traced in its structure. What- 

 ever may be its origin, it is obviously useful in protecting 

 the foetus from being injured by any sudden shock, or com- 

 pression. 



The chorion, in'many animals, serves the purpose of a sup- 

 port to the vessels which form the umbilical cord. It joins 

 the amnios at the umbilical cord, and is united with the uterus 

 wherever there is a placenta. In the sow and mare it is 

 united to the whole internal surface of the uterus by nume- 

 rous tubercles. In the ruminating quadrupeds these tu- 

 bercles appear to collect in groups, which have been termed 

 cotyledons. These consist of the glandule uterina or fleshy 

 excrescence of the inner surface of the uterus, and the ca~ 

 runcula or corresponding glands of the chorion. In the 

 sheep and goat the glandulae are concave, and receive the 

 convex surface of the caruncula?, while this arrangement is 

 reversed in the cow and deer. The third kind of placenta 

 may be considered as arising from the more complete union 

 of the tubercles, not into cotyledons, but into two masses, 

 sometimes only one, either lying close together, or spread 

 out like a belt. 



In many quadrupeds there is a peculiar sac, termed 

 alkintoiS) which occurs between the amnios and chorion in 

 some cases, as the mare, occupying the whole cavity ; in 

 others, as the sheep and cow, it is more limited in its ex- 



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