454 ON INCREASE IN SIZE [pt. iii 



would have reached had it gone on growing at the same velocity 

 as before birth. 



This leads on to the general problems raised by the growth of the 

 ductless glands in the embryo, problems of the greatest importance 

 in view of the regulating influence which the foetal endocrines 

 probably exercise. The pituitary gland, according to Covell, grows 

 proportionately to the total body-weight in human pre-natal life, 

 i.e. slowly till about the 5th month and more rapidly thereafter. 

 The thyroid also shows no outstanding variations from the normal 

 curve. The growth of the thymus, however, is characterised by high 

 variability, while the pineal gland grows at nearly the same rate as 

 the brain. The results of studies on the weight of these glands, 

 therefore, do not reveal any striking correlations, and they must be 

 supplemented by histological evidence. This will be presented in the 

 section on hormones. 



Scammon; Scott; and Scammon & Kittleson have studied the 

 growth of the intestinal tract and the stomach in the human embryo. 

 While this work does not give us any help in evaluating the active 

 absorptive surface during embryonic life, its main conclusions are of 

 interest. Thus the growth of the gastro-intestinal tract follows the 

 law of antero-posterior gradient or direction, for the more cranial 

 portions grow relatively more rapidly in the early part of foetal life, 

 while the successive caudal portions show smaller amounts of growth 

 at the beginning and larger ones later. The number of crypts and 

 glands in the stomach mucosa seems to increase per sq. mm, very 

 regularly during the progress of foetal growth. Watkins' study of the 

 growth of arteries is also interesting, for it shows that the vessels 

 which supply the foetus only have a rate of growth similar to that 

 of the body as a whole, i.e. slow for a short time at first, and then 

 for a long time rapid, while the arteries which supply the placenta 

 as well as the embryonic body have a long period of slow growth 

 followed by a short period of rapid growth. These facts throw a 

 certain light on the metabolic needs of the developing organism. 

 Much valuable information is contained in the papers of Scammon 

 and Armstrong on the foetal growth of the eye, and in that of Noback 

 on the respiratory system, but it cannot be given here. 



Davenport has recently considered the growth-curves of man in 

 the light of the work of Scammon and his associates, and Gunther 

 has written on these subjects especially in relation to sex. 



