15G 



WEIGHT, SIZE, AND AGE OF THE HUMAN EMBRYO. 



for a given sitting height is about 30 per cent. But since the weekly weight incre- 

 ment is about three times greater in its percentage than the sitting-height incre- 

 ment, the difference in accuracy in their use for the determination of age is slight. 

 Their accuracy is greater in the earlier weeks and becomes progressively less toward 

 the later weeks, varying from about 4 days at the fourteenth week to over 3 weeks 

 at the thirty-fifth week. The joint use of the two determinations, however, corre- 

 spondingly increases the accuracy of the age estimation. 



For convenience of reference, these data have been tabulated in table 3. It is 

 to be remembered that these figures are based on only 704 specimens and additional 

 material may modify them somewhat; but it is probable that they are adequate to 

 establish the essential character of these relations. 



Table 3. — Relative variation of silting height and weight, showing extent of possible error in estimating <igr on either 



sitting height or weight. 



14 th week: 



Sitting height 

 Weight 



17th week: 



Sitting height 

 Weight 



20th week: 



Sitting height 

 Weight 



25th week: 



Sitting height- 

 Weight 



30th week: 



Sitting height 

 Weight 



35th week : 



Sitting height 

 Weight 



Mean. 



S7 mm. 

 45 gin. 



130 mm 

 150 gm. 



164 mm. 

 31G gm. 



218 mm. 

 723 gm. 



20.5 mm. 

 1,323 gm. 



311 mm. 



2,274 gm. 



Normal 

 minimum. 



85 mm. 

 38 gm. 



125 mm. 



135 gm. 



155 mm. 



275 gm 



207 mm. 

 615 gm. 



252 mm. 

 1,150 gm. 



295 mm. 



1,970 gm. 



Normal 

 maximum. 



92 mm. 

 52 gm. 



135 mm. 



170 gm. 



172 mm. 

 367 gm. 



229 mm. 

 845 gm. 



277 mm. 

 1,550 gm. 



327 mm. 

 2,650 gm. 



Range of 

 variation. 



7 mm. 

 14 gm. 



10 mm. 

 35 gm. 



17 mm. 

 92 gm. 



22 mm. 

 230 gm. 



25 mm. 



400 gm. 



32 mm. 

 680 gm. 



Possible 

 error. 



4 days. 



5 days. 



5 days, 



days. 



1 h weeks. 

 1| weeks. 



2 weeks. 

 2k weeks. 



2 ] weeks. 



3 weeks. 



3^ weeks. 



3J weeks. 



FOOT LENGTH. 



For purposes of determining age, neither the foot length nor the head size, 

 when used alone, has as much value as do weight and sitting height. The head size 

 shows considerable variation, due in part to the mechanical molding which occurs 

 in the great majority of specimens and in part to the varying effect of formalin on 

 the soft tissues of the scalp, the distention of which affects the size reading consid- 

 erably more than the corresponding increase in the sitting height. The foot 

 length, as compared with the sitting height, possesses the disadvantage of being 

 smaller and having a smaller weekly increment. Nevertheless, these two measure- 

 ments serve as additional controls, and in cases of dismembered specimens they 

 often constitute the only reliable criteria for the determination of the age. From 

 an uninjured foot one can determine fairly closely the normal sitting height, weight, 

 and menstrual age of the specimen by means of the respective correlation curves. 



Accurate measurement of the foot can not be made earlier than in embryos 

 about 24 mm. long. Briefly stated, the mean foot length at different intervals is 

 as follows: at 8^ weeks, about 4 mm.; end of the eleventh week, about 7 mm.; 

 end of the fourteenth week, 14 mm. ; end of the sixteenth week, about 20 mm. ; 

 end of the twenty-second week, about 40 mm.; end of the thirtieth week, about 



