WEIGHT, SIZE, AND AGE OF THE HUMAN EMBRYO. 



159 



From an examination of the table, it will be seen that the actual increment in 

 head size undergoes a slight gradual decline from the twelfth to the fortieth week, 

 decreasing from 13 mm. to 5 mm. Expressed in terms of percentage the decrease 

 is greater, being from 20 per cent to about 2 per cent. As in the case with sitting 

 height, the greatest increments are before the eighteenth week. The decrease in 

 the percentage increment is a little greater in the head modulus than in the sitting 

 height, and its mean curve, as seen in charts 3 and 5, gradually recedes from the 

 mean curve of the latter. On this account the head modulus, though at first 

 nearly equivalent to the sitting height (96 per cent), toward the end of pregnancy 

 is less than 84 per cent. In a few outlying instances the head modulus equals or 

 exceeds the sitting height. These are cases showing unusual distention of the soft 

 tissues of the seal]). Under the usual conditions, if the head modulus is greater 

 than the sitting height it should be regarded as abnormal. In this way we may 

 be able to detect early cases of hydrocephalus. On the other hand, if the head 

 modulus is too small we have an indication of microcephalus. 



BIBLIOGRAPHY. 



Mall, F. P., 1910. Determination of the age of human 

 embryos and fetuses. Manual of Human Em- 

 bryology (Keibel and Mall), vol. 1, p. 180-201. 



, 1918. On the age of human embryos. Amer. 



Jour. Anat., vol. 23, pp. 397-422. 



Meyer, A. W., 1914. Curves of prenatal growth and 

 autocatalysis. Arch. f. Entwicklungsmechanik 

 der Organismen, vol. 40, pp. 497-525. 

 — . 1915. Fields, graphs, anil other data on fetal 

 growth. Contributions to Embryology, vol. 2, 

 pp. 55-68, Carnegie Inst. Wash. Pub. 222. 



Iin;c;s, T. F., 1904. A comparative study of white and 

 negro pelves, with a consideration of the size of 

 the child and its relation to presentation and char- 

 acter of labor in the two races. Johns Hopkins 

 Hosp. Reports, vol. 12, pp. 421-454. 



Schtjltz, A. H, 1919. Changes in fetuses due to for- 

 malin preservation. Amer. Jour. Phys. Anthro- 

 pol., vol. 2, pp. 35-41. 

 — , 1920. An apparatus for measuring the new- 

 born. Johns Hopkins Hosp. Bull., vol. 31. 



Zangemeister, W., 1911. Die Altersbestimmung des 

 Foetus nach graphischer Methode. Zeitschr. f. 

 Geb. u. Gyn., vol. 69, pp. 127-142. 



Tables 6 and 7 constitute a list of normal embryos of the Carnegie Collection 

 on which the correlation curves of sitting height, weight and menstrual age are 

 based. The material is arranged according to weight, i. e., its formalin weight 

 after being in a 10 per cent solution about two weeks. Some of the specimens of 

 over 400 grams in weight were injected with the formalin solution through the um- 

 bilical vessels, as noted under "Remarks"; in such cases the weight given is the 

 fresh weight plus 5 per cent, this being more nearly comparable to the weight of 

 specimens simply immersed in the solution. The sitting height of specimens 50 

 mm. long and over was measured with the body held as straight as possible. Speci- 

 mens smaller than this were usually measured in their natural curved posture. 

 In the overlapping field both measurements are given, as seen in table 6. By 

 head modulus is to be understood the mean between the greatest horizontal circum- 

 ference of the head and the biauricular transverse arc . The estimated menstrual ages 

 of the specimens are based on the curve in chart 6, with the exception of the first 

 8 specimens in table 6, the ages of which are based on the estimates of Mall (1910). 



