GROWTH OF THE SKELETON 299 



In the figures as published there is no conclusive evidence 

 for a difference according to sex or to age between birth and 

 maturity. 



When the foregoing data for the rat are compared with those 

 for man, it appears that in man there is no phase of relatively 

 rapid growth of the skeleton in weight during the period just 

 after birth. Further, there does not appear in man a regular 

 diminution in the relative weight of the skeleton during the 

 period preceding puberty corresponding to the period in the rat 

 during which the relative weight falls from 10 per cent to 7 per 

 cent as shown in our table 2. It should be reiterated, however, 

 that the data for man are very incomplete. 



At maturity the percentage weight of the moist skeleton in man 

 (16 per cent) is higher than that in the ligamentous skeleton (11 

 per cent) or in the cartilaginous skeleton (5 per cent) of the 

 albino rat. Since the form of the rat body is so different from 

 that of the human body in which the limbs are relatively much 

 longer, it is not surprising that the relative weights of the skeleton 

 at maturity should be dissimilar, but the apparent constancy of 

 the relative weight in man from birth on is a matter of some 

 interest. 



Theile ('84) made studies of the human skeleton according to 

 a plan fairly comparable with our own, but these were confined to 

 the first seven years of life. In so far as we can compare our 

 results with his, it appears that the relative growth of the parts 

 of the skeleton, compared with one another, takes place in man in 

 the same manner that it does in the rat. 



The observations of Stratz ('09) in man show also the relatively 

 slower growth of the head, as noted for the cranium of the rat 

 (p. 299) as well as the relatively slower growth of the arms in 

 length. Indeed, at maturity Stratz gives the arm length as 80 

 per cent of the leg length, and this is the same ratio as is found 

 in the rat for the length of the humerus plus ulna divided by 

 that of femur plus tibia, as shown in table 27 and chart 22. 



When the relative length of the humerus plus radius to femur 

 plus tibia is computed, it is found to range in the rat from 94 

 per cent at 5 grams of body weight to about 71 per cent at 40 

 grams, after which it varies but slightly (chart 22, table 27) . 



