DISEASES OF THE OX AND SHEEP. 645 



The fertilised ovum, having escaped from the ovary, is seized 

 or entangled by the fimbriated extremity of the Fallopian tube, 

 and subsequently passed along the tube into the uterus. If it 

 be not caught by the fimbria, the ovum falls into the cavity of 

 the abdomen, where it may perhaps become an extra-uterine 

 foetus, as occasionally occurs both in human beings and in 

 animals. During the passage of the ovum into the uterus, it is 

 covered by a membrane called the chorion, by means of which 

 the developing foetus becomes attached to the inner surface of 

 the womb, and obtains from the parent the materials necessary 

 for the maintenance of life and development. In the case of the 

 cow and the ewe and certain other animals, the outer surface of 

 the chorion is thickly studded with shaggy projections called 

 cotyledons. These are attached to corresponding concavities 

 in the membrane lining the wall of the uterus internally, 

 the tunica decidua uteri, which contains the enlarged and elon- 

 gated branches of the uterine arteries of the mother. It is by 

 the medium of them that the minute branches of the blood- 

 vessels of the mother and those of the foetus come into contiguity, 

 although they do not enter into direct communication with one 

 another. Hence, the two sets of blood-vessels lying in contact, 

 the blood of the foetus is purified by means of the more highly 

 oxygenated blood of the mother. The cotyledons may then 

 be looked upon as subserving in some degree the functions 

 of respiratory organs, and to some extent also as organs of 

 assimilation. 



The chorion consists of the false amnion fused with the 

 allantoid membrane. In addition to the chorion there is 

 also another membrane enveloping and immediately surrounding 

 the foetus. This is called the true amnion or water-bag, which 

 contains the fluid in which the foetus floats. By means of this 

 fluid, the liquor amnii, the foetus is protected from injuries, 

 which might otherwise destroy its life. This fluid also, con- 

 tained in its investing membrane, is also protruded into the 

 mouth of the womb at the commencement of the act of parturi- 

 tion, thus acting as a hydrostatic dilator. The rupture of this 

 bag, or rather the consequent escape of the fluid contained 

 within it, is one of the earliest signs heralding the act of parturi- 

 tion. The space Intervening between the chorion and the 

 amnion acts as a receptacle for the urine of the foetus. The 



