Prenatal Growth of the Human Body. 121 



For the specimens sectioned, it must also be remembered that the 

 process of dehydration and embedding in paraffin causes a shrinkage 

 of at least 20 per cent, or more than enough to counterbalance the , 

 swelling due to the formalin fixation. It is improbable, however, 

 that the errors from these sources are large enough to affect materially 

 the main conclusions concerning growth, especially concerning the 

 relative growth of the various parts. 



In the following pages there will be considered briefly : first the pre- 

 natal growth of the body as a whole, then the relative growth of its 

 principal parts, and finally the relative growth of most of the indi- 

 vidual organs. For the organs and parts, it has been found more 

 convenient and useful to record the relative size, expressed in per- 

 centage of the entire body. From these data, the absolute size of any 

 part can easily be calculated, if desired (that of the whole body being 

 given). 



1. Growth of the Body as a Whole. 



In Table I, a list is given of the 43 specimens upon which my own 

 observations were made. In the first column, the catalog numbers 

 (in my collection) are indicated. In estimating the age of the speci- 

 mens, Mall's rule was used for the first four months and Hasse's rule 

 for the last five months. In the fifth month, a compromise was used 

 between figures derived from Mall's method and those from Hasse's. 



In Table II, some observations upon the volumes of the His-Ziegler 

 models are recorded. The embryos corresponding to these models 

 have been figured and described in detail by His (23), who gives no 

 data concerning their weight or volume, how^ever. 



While a considerable amount of data has accumulated concerning 

 the growth of the fetus from the 4th to the 10th month, very few 

 observations! have been made upon the earlier embryos. In fact up 

 to this time no data have been published which allow any accurate 

 conclusions concerning growth in the human embryo during the first 

 three months. My own observations include, in addition to the seven 

 His-Ziegler models, eighteen embryos within this period. Two of 

 these embryos (6 mm., 7.3 mm.) are of the 1st month, six of the 2d 

 month; and ten of the 3d month. Four of these embryos (6 mm.. 



