PRENATAL GROWTH OF THE PIG 137 



per cent near birth. In the adult, they form only 0.011 per cent 

 of the body. 



7. The heart forms 4.64 per cent of the body weight at 15 mm., 

 decreasing to about 1 per cent near birth, and averaging about 

 0.75 per cent during the greater number of the prenatal stages 

 examined. In the adult hog, the heart averages 0.32 per cent 

 of the body weight. 



8. The lungs increase to a maximum of 3 . 9 per cent of the 

 total body weight at 86 mm., decreasing irregularly thereafter 

 to about 2 per cent near birth. The right lung is larger than 

 the left in the approximate ratio of 7 to 5. The lungs in the adult 

 form only about 0.7 per cent of the body. 



9. The liver increases to a maximum relative size of 15.88 

 per cent of the body weight at 25 mm., decreasing to 3 . 1 per cent 

 near birth. Its maximum relative size is over twice as large as 

 that of the human. In the adult the liver of the pig averages 

 1 . 38 per cent, being only about half that of the human. 



10. The kidneys increase rapidly to a maximum relative size 

 of 2.59 per cent of the body weight at 58 mm., decreasing there- 

 after to an average of 1.01 per cent near birth; forming about 

 0.25 per cent in the adult. The Wolffian bodies are at first 

 relatively enormous, forming over 12 per cent of the body weight 

 at 15 mm. They decrease rapidly, however, in relative (and, 

 after 58 mm., in absolute) size. 



11. The spleen, pancreas and thymus increase gradually 

 from the beginning, averaging about 0.17 per cent, 0.16 per 

 cent, and 0.37 per cent respectively, of the total body weight 

 near the end of fetal life. In the adult the figures are 0. 13 per 

 cent and 0.14 per cent for spleen and pancreas respectively. 



12. The thyroid gland after 58 mm. decreases slightly in 

 relative size throughout prenatal growth, averaging about . 026 

 per cent of the body at the close of the fetal period, and 0.004 

 per cent in the adult. 



13. The suprarenals form about 0.13 per cent of the body 

 at 58 mm., decreasing thereafter to about 0.019 per cent near 

 birth, and about . 005 per cent in the adult. 



