WEIGHT, SIZE, AND AGE OF THE HUMAN EMBRYO. 



157 



60 mm.; and at term it averages 82.5 mm. If the foot length is plotted as a curve 

 at weekly intervals from the eighth week to term it will be found that the growth is 

 relatively slow at first and does not reach its maximum weekly increment until 

 about the fourteenth week, after which there is a weekly increase of about 3 mm., 

 continuing with slight variation to term. The growth is a little more rapid from 

 the fourteenth week (CR 87 mm.) to the twenty-sixth week (CR 228 mm.) and a 

 little less rapid from then until term. 



Table 4. — Fool length nrtd ils proportion to silting height. 



The foot length of our individual specimens has been entered in the form of 

 dots on charts 1, 3, and 5, showing the length in millimeters correlated to both 

 sitting height and weight. The pathway occupied by the dots, aside from a 

 few outlying ones, is smooth and distinct. When the upper and lower margins 

 of this pathway are outlined it gives the maximum and minumum foot lengths at 

 the different intervals. These readings are entered in the accompanying table 4. 

 The average of the maximum and minumum lengths is entered as the mean foot 

 length. There is also entered in the same table the percentage of the sitting height 

 formed by the mean foot length for the end of each week. Examination of this 

 table shows that there is a gradual increase in the length of the foot relative to the 

 length of the embryo. This does not begin, however, until the fetus is about 70 

 mm. long. From 30 mm. to 60 mm. the foot grows less rapidly than the body as a 

 whole. Beyond 70 mm. there is a slight gradual increase in the length of the foot 

 in proportion to sitting height, so that during the last month the foot length is 

 23 per cent of the sitting height, having increased from about 15 per cent, which 

 existed in fetuses 70 mm. long. This increase in the percentage of the foot length 

 to sitting height is not so much due to an acceleration in the growth of the foot 

 as to a retardation in the increase in sitting height that characterizes the latter 

 part of fetal growth. 



HEAD MODULUS. 



As an index of head size a modulus was selected, consisting of the mean of the 

 greatest horizontal circumference of the head and the biauricular transverse arc 

 (i. e., the distance from one external auditory meatus over the vertex of the head to 



