FORM AND GROWTH 



1 2 l 



The thoracic and abdominal 

 viscera as a group (Figure 74) 

 appear more irregular in rela- 

 tive size. Of the three species 

 for which prenatal data are 

 available, the viscera of the 

 pig are relatively much larger 

 than those of man and dogfish. 

 In all three the viscera at first 

 increase in relative size, then 

 decrease to birth. From birth 

 to adult, the viscera in man 

 and pig decrease, remaining 

 closely parallel with each 

 other. In the chick, the viscera 

 are in the early postnatal pe- 

 riod relatively much larger 

 than in the other animals. In 

 the chick, rat, and dogfish, 

 there is also a postnatal in- 

 crease to a temporary maxi- 

 mum in relative visceral size 

 (weight), and in the last two 

 the adult thoracic-abdominal 

 viscera appear relatively 

 slightly greater than at birth. 



The weight curves for the 

 whole visceral group are of 

 course dominated by the larger 

 organs, especially the alimen- 

 tary tract, heart, lungs, and 

 kidneys. This obscures the fact 

 that there are very marked 

 differences in growth among 

 the individual organs in all 



Maximum 

 postnatal Adult 



Drain — Pehtii/e Weight 



Figure 75. Graph showing changes in the 

 relative weight of the brain in different 

 species at various stages, prenatal and post- 

 natal. Data from Bessesen and Carlson, 

 Jackson, 20 - 22 Kearney, 27 and Latimer. 31 



Early Maximum 



embryonic prenatal Natal 



Maximum 

 postnatal 



VI5CERA -P<?/<3MW 



Figure 74. Graph showing changes in the 

 telative weight of the viscera (thoracic and 

 abdominal group) in different species at 

 various stages, prenatal and postnatal. Data 

 from Bessesen and Carlson, Jackson, 20 - 22 

 Jackson and Lowrey, 20 Kearney, 27 Latimer, 31 

 and Lowrey. 35 



