44:8 GENERATION. 



dates more nearly from a menstrual period prevented than 

 from the last appearance of the flow, it would be necessary to 

 assume that ovulation usually takes place before the flow, and 

 fecundation would be most liable to follow intercourse occur- 

 ring at that time ; for we could hardly admit that an ovum, 

 fecundated at the cessation of a menstrual period, could re- 

 main in the generative passages of the female for two or 

 three weeks, before the mucous membrane of the uterus is 

 prepared for its reception. These facts are so strong, that 

 the view advanced by Loewenhardt, and apparently supported 

 by the researches of Kundrat and Engelmann, cannot yet be 

 adopted without reserve. 



As regards the practical applications of calculations of 

 the probable duration of pregnancy in individual cases, we 

 must recognize the fact that the duration is variable. If we 

 date from the end of the last menstrual period, we may 

 adopt the average of 278 days, a little more than nine calen- 

 dar months. If we adopt the view that pregnancy dates 

 from a menstrual period which has been prevented, the dura- 

 tion of intra-uterine life would be about 250 days. 



Size, Weight, and Position of the Fmtus. The estimates 

 of writers with regard to the size and weight of the em- 

 bryon and foetus at different stages of intra-uterine life pre- 

 sent very wide variations ; still, it is important to have an 

 approximative idea, at least, upon these points, and we shall 

 adopt the figures given by Scanzoni, as presenting fair aver- 

 ages. As the measurements and weights are simply approxi- 

 mative, the slight differences between the German and the 

 English standards are not important. It will be useful, also, 

 to give, as is done by Scanzoni, a review of the general de- 

 velopment of the organs at different stages. 1 



At the third week, the embryon is from two to three 

 lines in length. This is about the earliest period at which 

 measurements have been taken in the normal state. 



1 SCANZONI, Lehrbuch der Geburtshilfe, Wien, 1867, Bd. i., S. 89, et seq. 



