256 



Anatomy and Physiology of the 



ova-sac is seized or entangled by the fimbriated edge of the 

 Fallopian tube, and subsequently conducted into the uterus, 

 where it excites that extraordinary action which leads to the for- 

 mation of a new creature in every essential particular like its 

 parent. Should the ovum not be caught by the fimbria, it falls 

 into the cavity of the abdomen, but is not necessarily destroyed, 

 as even here, although out of its proper matrix, it sets up an 

 analogous action to that which otherwise would have been pro- 

 duced within the uterus. Thus we have explained the formation 

 of those extra-uterine foetuses, which are occasionally met with 

 both in human and veterinary practice. 



Without describing the earliest stages of the formation of the 

 foetus from the impregnated ovum, it will be sufficient to remark 

 that in the descent of the ovum into the uterus it receives a 

 coating of effused fibrin, which forms the membrane termed the 

 corium, by which the foetus is attached to the inner surface of 

 the womb, and obtains from the mother the materials necessary 

 for its vitality and growth. The outer surface of the corium (see 

 Plate) is thickly studded in the cow and ewe with shaggy pro- 

 jections, c, named cotyledons, and these are fitted into corre- 

 sponding concavities, b, in the membrane lining the womb, the 

 tunica decidua uteri, thus forming the bond of connexion we have 

 spoken of. The tufts of the corium contain the ramification of the 

 foetal vessels, and the concavities of the tunica decidua uteri the 

 enlarged and elongated branches of the uterine arteries of the 

 mother : thus by the two sets of vessels lying in contact, the blood 

 of the foetus is purified and reinvigorated, as the maternal blood 

 is more highly oxygenated than that of the foetus. The change 

 which is effected is a chemical one, and analogous to that taking 

 place in the lungs of an animal after birth ; the cotyledons, there- 

 fore, may so far be regarded as the foetal lungs. Besides this 

 important office performed by them, the vessels of the foetus are 

 here surrounded by a thick layer of cells which absorb nutrient 

 matter from the mother and transmit it to the blood of the foetus. 

 Hence the cotyledons may also be compared to the stomach, or 

 rather to the digestive and assimilative organs of a perfect 

 animal. Thus it will be seen that although there is no direct 

 communication between the vessels of the mother and those of 

 the foetus, yet every requisite for its life and growth is provided 

 for. 



Besides the corium, there are two other membranes to be 

 noticed as belonging to the foetus, the amnion, y, and the allan- 

 toid, e. The amnion immediately surrounds the body of the 

 foetus, and secretes a fluid, the liquor a?nnii, in which it floats, and 

 by which it is protected from those injuries which might otherwise 

 destroy its life : it being a property of fluids to diffuse and modify 



