NUTRITION OF THE FCETUS 25 



length of tlie foetus toward the 32d week is 65 cm. (Gurlt), and 

 toward the end of this month 75 cm. (Frauck). 



In the beginning of the ninth month the whole body 

 is covered with hair and increases greatly in size. The foetus 

 measures from 80 to 100 cm. In the beginning of the tenth 

 month the foetus becomes mature. 



3. — Nutrition of the Fcetus. 



For the development of the ovum, nutritive elements are 

 essential. When these are wanting, the egg perishes. Already 

 in the ovary the ovum is nourished by the leucocytes ; there- 

 fore it is reasonable to presume that nutrition after conception 

 during the pre-placental period, takes place in this manner. 



Uterine milk, essentially composed of leucocytes in various 

 phases, may furnish the food. The cells of the ectoderm 

 receive and prepare the nutriment. The material thus received 

 first serves to enlarge the resorbing surface by multiplying 

 the cells of the ectoderm, and only when this has progressed 

 to a certain degree the embryo begins to develop (Bonnet). 



In a later embryonic period the umbilical vesicle, with the 

 omphalo-mesenteric vessels, forms. The embryo is nourished 

 by the umbilical vesicle — that is, by the smaller branches of 

 the omphalo-mesenteric vein ( Vena oinphalo-mesenterica). The 

 heart then carries the nutritious elements to all parts of the 

 embryo. 



This early circulation, which might be called the omphalo- 

 mesenteric circulation (circulatio omphalo mesenterica), exists, 

 same as the umbilical vesicle, only for a time. When the 

 latter disappears, and the allantois forms, it is replaced by 

 the placental circulation, representing the foetal circulation 

 (Fig. 10). By means of this circulation, the blood which 

 circulated in the foetus is taken to the foetal placenta and 

 reaches the smaller vessels of the chorion. Here its com- 

 position experiences changes and then returns to the foetus. 

 In the placenta an exchange of oxygen for carbon dioxide 

 occurs, the circulation at this part fulfilling the same purpose 



