APFEXDAdES OF THE F(ETUS. 81 



that invests the young animal at birth, is due to the precipitation on its 

 skin of the mucus and yellow matter contained in this lluid. Hoppe- 

 Seyler gives its cliemical composition as water, holding in solution a 

 small quantity of casein, kreatin, lactic acid, grape-sugar, and saline 

 matter, and therefore resembling very dilute serum. 



The «5t'5 of the //(/uor a??in»" are varied and important. It is not very 

 probable that it serves as nutriment for the fa'tus in the early period of 

 intra-uterine life ; though it has been found in the stomach of those 

 young animals which had been purposely fro/en in their membranes, and 

 then dissected ; portions of the hoof epithelium have also been dis- 

 covered in the fcctal stomach. It preserves an equable temperature for 

 the young creature; maintains the integrity of its exterior before the skin 

 is covered by the peculiar sebaceous coating ; favours its movements and 

 its development, by removing it from unequal pressure ; diminishes the 

 impression from sudden external movements and shocks, thus preserving 

 it from injury ; and allows it to obey the laws of gravitation. It also pro- 

 tects the mother from injury by the foetus, towards the termination of 

 gestation. During parturition, it protrudes the membranes ; is the primary 

 agent in dilating tlae os uteri ; shields tlie foetus from the direct action 

 of the uterine contractions, whose violence might compromise its 

 existence ; renders the dilatation of the os easy and prompt ; and, 

 finally, by lubricating the vagina, causes the passage of the fotus 

 through it to be more gentle and expeditious than it would otherwise 

 be. 



Differences in the Amnion of other Animals. 



Biiminants. 



The amnion in Ruminants is similar to that of the Mare. It is eauly 

 separated into two layers, and shows on its inner surface, particularly 

 near where it invests the umbilical cord, a large number of whitr or 

 yellowish- white bodies. In the Cow these are sometimes elongated in 

 the form of papillae; at other times they exist in flattened, slightly 

 raised patches, about one-fourth of an inch long. Sometimes they are 

 single ; occasionally they are in clusters. They consist of large, flat, 

 nucleated cells, resembling a squamous epithelium ; it is concluded 

 that they are the seat of formation of a glycogenic material. Up to a 

 certain period of intra-uterine life they increase in size, and then 

 degenerate — their organization and development being in inverse relation 

 to the development of the liver, whose function they assume, with regard 

 to glycogenation. Externally the amnion is altogether in contact with 

 the allantois and chorion. 



Puj. 



It does not differ in the Pig. 



Difch and Cat. 

 In the Bitch and Cat the amnion is entirely covered by the amniotic 

 layer of the allantois, to which it adheres in the same manner as in the 

 ^lare ; the two membranes are only separated by the umbilical vesicle, 

 and there is no trace of the pouch and vascular plexus seen in that 

 animal. In the amniotic liquid, crumbs of meconium are found towards 

 the end of gestation. 



Allantois. 

 The allantois arises on the front part of the posterior extremity of the 

 mucous layer which is closing to form the intestine, as a growth of the 



6 



