430 VETERINARY LECTURES 



GESTATION, ABORTION, ETC. 



756. Average Periods of Gestation : 



Mare — Eleven months, but varies from 11 to 12 months. 

 Cow — Nine months, also varies. 



Sheep 1 , , , 



^ y Five months, or from 20 to 22 weeks. 



Goat J 



Pig— Four months, or from 15 to 17 weeks. 

 Bitch— Nine weeks, or from 58 to 65 days. 

 Cat — Eight weeks, or from 50 to 60 days. 



757. Impregnation of the ovum of the female takes place when 

 it meets the spermatozoa contained in the spermatic fluid of the male ; to 

 do so it usually travels from the ovary to the womb by the action of the 

 fringes of the Fallopian tubes, which grasp the ovum, and convey it 

 along one of these tubes into the womb. Impregnation may also take 

 place in the Fallopian tube itself. When impregnation occurs, a 

 series of changes begin in the womb. The segmentation of the 

 ovum, and development of the foetus and its membranes, are of too 

 complex a nature to be dealt with in this lecture, but the placenta, or 

 cleansing, is deserving of a short description. 



758. The Foetal Membranes (Placenta, or Cleansing— Plate 

 XLIL, Nos. 1 to 3) are three in number— namely, the amnion, 

 allantois, and chorion. 



759 .__The Amnion, or Slime Bag, is thin and transparent, and 

 in it floats the foetus, surrounded by slime. The allantois, or water- 

 bag, is situated outside of the amnion, and between it and the chorion. 

 The chorion is situated next the womb, and is the vascular coat. A 

 marked difference is seen in the attachment of this coat in the mare 

 as compared to those of the cow and sheep. In the latter there are a 

 large number of cotyledons, or rose-buds, consisting of ramifications 

 of foetal bloodvessels, which are intimately connected with similar 

 structures on the womb. In the mare, however, the attachment 

 is brought about by villi — small sprout-like projections — which are 

 found all over the outside of the placenta, and are received into corre- 

 sponding depressions in the mucous membrane of the womb. 



