QUESTIONS AND ANSWERS 271 



causes inanition and thereby prevents the mother from properly 

 nourishing the foetus. 



Give the function and describe the early development of the placenta. 



The function of the placenta is to establish communication be- 

 tween the mother and foetus by means of the umbilical cord. 



In the mulberry stage (stage of morula), the zona radiata throws 

 out tufts, the primordial chorion, which unite with the uterine 

 mucosa. This zone soon becomes attenuated and disappears while 

 the blastoderm enlarges within it. But this primitive chorion is not 

 permanent, it is replaced by another, similar, but more efficient 

 structure. 



From the surface of the outer layer of the blastoderm, tufts or 

 villi grow out to extend into the uterine mucosa. Through these 

 villi, there is an exchange of nutritive material and waste products 

 between mother and foetus. This is later supplanted by a permanent 

 attachment, formed by the tufts of the allantois which grow out 

 through the amniotic chorion to gain an intimate relation with the 

 blood-vessels of the uterus. 



Describe the phenomena of nutrition in the foetus. 



Before the placenta is formed, the ovum is bathed with an albu- 

 minoid substance which nourishes it during early development. 

 Later with the development of the placenta, which brings the capil- 

 lary systems of the mother and foetus into the closest relationship, 

 nourishment passes to the foetus by osmosis. 



Define (a) zonary placenta, (b) diffuse placenta, (c) cotyledonary 

 placenta. 



(a) A placenta which is band-like in form. In the bitch and 

 cat, the placenta forms a thick, annular band, or zone, about one 

 and one-half inches wide, passing around the middle of the chorion. 



(b) A diffuse placenta is one in which the chorionic villse are 

 diffused over the entire surface of the chorion. Seen in the mare 

 and sow. 



(c) A placenta in which the viUi are restricted to certain areas 

 (80 to 100 in number) called cotyledons. Seen in cows and sheep. 



Mention the animals in which cotyledons are found. 



Cow, sheep and goat. 



Describe the umbilical cord and state its function. 



The umbilical cord is a collection of vessels which extends from 

 the placenta to the fetal umbilicus. It is about 35 inches long in 

 the mare and 15 inches in the cow. It is formed by the allantoic 



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