GESTATION, ABORTION, &c. 



751. The Average Periods of Gestation are : — 



Mare — 11 months, but varies from 10 to 12 months. 



^ Cow — Nine months, also varies. 



Sheep — ^ _. , . 



_ ' i-ive months, or irom 20 to 22 weeks. 



Goat — i 



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



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



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



752. For impregnation, the ovum of the female must meet the 

 spcnnatozoii contained m 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. 



753. The Foetal Membranes (Placenta or Cleansing — Plate 

 XXXIX., Nos. 1 to 4), are three in number, namely, tlie Amnion, 

 Allantois, and Chorion. 



754. The Amnion or Slime Bag is thin and transparent, and in it 

 floats the fcetus, 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 rosebuds, consisting of ramifications 

 of fcetal blood-vessels, which are intimately connected with similar 

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



