PRENATAL GROWTH OF THE PIG 109 



The following measurements were made on each pig: weight 

 and crown-rump length were observed for the whole body ; the 

 head, brain, eyeballs, spinal cord, thyroid gland, thymus gland, 

 right lung, left lung, heart, liver, stomach and intestines (with 

 mesentery and contents, also without contents where possible), 

 spleen, pancreas, suprarenal glands, gonads, kidneys and Wolffian 

 bodies, were each weighed separately. 



The weights were taken carefully, the organs being placed in a 

 closed glass vessel of known weight. For the larger fetuses, the 

 organs were weighed to 0.001 g. (1 mg.), the body and head being 

 weighed to 0.1 g. For the smaller embryos (18 mm., 25 mm., 

 37 mm., 41 mm.), the body and head were weighed to 0.001 g., 

 and the organs (except those weighing more than 10 mg. in the 

 37 mm. and 41 mm. embryos) were weighed to . 0002 g. (0 . 2 mg.) . 

 For the 15 mm. embryos, the body and organs were weighed to 

 0.0001 g. (0.1 mg.). 



The head was divided from the neck on a plane passing just 

 behind the angle of the mandible and the cranium. Variations 

 in this plane, which to a certain extent are unavoidable, lead to 

 variations in the observed weight, and therefore in the relative 

 size of the head. 



The organs were weighed with contained blood, except the heart, 

 which was opened and cleaned of the blood in the cavities. The 

 brain and spinal cord were weighed with the pia mater but with- 

 out the dura mater. 



Since the age of the specimens is unknown, it is impossible to 

 construct accurate curves of growth either for the body as a whole 

 or for the various organs. How^ever, by arranging the figures 

 representing the relative size (per cent of the net body weight) 

 according to the crown-rump length, curves can be drawn which 

 give an approximate idea of the changes in the relative growth 

 of the various organs during prenatal life. But no definite con- 

 clusions can be draw^n from these curves as to the rapidity with 

 which these changes in relative size take place. The only excep- 

 tion to this is in the case of the body as a whole, w^here some data 

 by Keibel on the age of young pig embryos make it possible to 

 compare the growth in the early part with that in the remainder 

 of the prenatal and with the postnatal period. 



