24 



MORPHOGENESIS 



of puberty. Puberty occurs earUer in the female, so that between the ages of 12 and 15 the 

 girls exceed the boys in average height and weight. With the exception of this period of accel- 

 eration, the (relative) growth rate in general diminishes steadily from birth, and has practically 

 ceased at 20 years. The average height at this time is about 160 cm. (5 ft., 3 in.) in the female, 

 and 170 cm. (5 ft., 7 in.) in the male; average weight, about 56 kilograms (126 lbs.) in the female, 

 and 65 kilograms (146 lbs.) in the male. Under favourable conditions, growth in height may con- 

 tinue slowly up to about 25 years, and in weight even longer; but in old age there is a slight 

 decrease in both height and weight. 



The following measurements (from Holt, "Diseases of Infancy and Childhood" 

 may be taken as a normal average standard of growth during the first three 

 years. The weights are taken without clothing. The height is taken by plac- 

 ing the baby on a perfectly flat surface hke a table, and having some one hold 

 the child's knee down so that he lies out straight, then taking a tape-measure 

 and measuring from the top of his head to the bottom of his foot, holding the 

 tape line absolutely straight. The chest is measured by means of a tape line 

 passed directly over the nipples around the child's body and midway between 

 full inspiration and full expiration. The head measurement is taken directly 

 around the circumference of the head, over the forehead and occipital bone. 



Relative growth of the parts. — The growth of the body is not uniform in the 

 various parts, and changes in proportions therefore occur during development, as 



Fig. 31. — Figures Illustrating the Changes in Proportion During Prenatal and 

 Postnatal Growth. (Stratz.) 



2 mo. (fasta\) 5 mo. Newborn 2 yrs. 6 yrs. 12 yrs. 25 yrs. 



shown in fig. o\. It will bt; not(!(l that the changes are in accordance with the 

 law of developmental direction previously explained, the growth impulse passing 

 along the body in a cranio-caudal direction. 



The head is therefore largest in the earlier stages, forming about lialf the body, decreasing 

 to 25 per cent, in tlic newborn, and to 7 or 8 per cent, of tlie body in the adult. The upper 

 limbs increase to ab(jut 10 per cent, of the body at l)irth, maintaining thereafter about the same 

 relative size. The trunk as a whole remains of about the same relative size (about 45 per cent.),. 



