88 



PROBLEMS OF RELATIVE GROWTH 



sheep and giraffe which together with inspection of skeletons 

 makes it fairly clear that in the phylogenetic elongation of the 

 giraffe's leg, the growth-centre has lain in the cannon-bone, 

 with a steep gradient distally, a less steep one proximally. 

 Meanwhile actual weight (and length) measurements made by 

 Hammond (1927, 1929) and analysed by Huxley (1931B) on 

 the individual growth of the hind-limbs in sheep, show that 

 in regard to the pelvis and the three segments femur, tibia 

 and cannon-bone (unfortunately the digits were not measured) 

 there is, correlated with the negative heterogony of the whole 



limb relative to the body, a reversed 

 growth-gradient with low point dis- 

 tally (Table VIII ; Fig. 49). Though 

 these constitute but two isolated bits 

 of evidence, they indicate, so far as 

 they go, that the growth-mechanisms 

 underlying all heterogony are similar, 

 and that when heterogony is negative, 

 the sign of the gradient is simply 

 reversed. 



Hammond (1928, see also 1921) 

 has also shown that the growth- 

 gradients in the limbs and elsewhere 

 affect the muscles as well as the bones, 

 so that the study is of practical as 

 well as theoretical importance. An 

 important point made by Hammond 

 may be given in his own words. 



Sheep 



Fig. 48. — Comparison of the 

 skeleton of the foot in Ox, 

 Sheep and Giraffe, to show- 

 graded alteration in propor- 

 tions of parts. 



To effect the transformation form 

 a typical (e.g. ox) form to that in 

 the giraffe, y — c has been enlarged, 

 c — b has remained nearly constant, 

 b — a has been decreased, and a — o 

 markedly decreased. In addition, 

 the length : width ratio has been 

 increased. 



"As the animal grows, it changes its 

 conformation ; at birth the calf or lamb 

 is all head and legs, its body is short and 

 shallow, and the buttocks and loin are 

 comparatively underdeveloped ; but, as it 

 grows, the latter — buttocks, loin, etc. — grow at a faster rate than the 

 head and legs, and so the proportions of the animal change. . . . 

 The extent to which these proportions change determines its con- 

 formation ; those which develop most for their age have the best meat 

 conformation, while those which develop least have the worst . . . 

 Breed improvement for meat, therefore, means pushing a stage fur- 

 ther the natural change of proportions as the animal matures. . . . 

 The adult wild Mouflon ewe is in its proportions but little in advance 

 of the improved Suffolk lamb at birth, although it is much larger. 



What this means to the butcher and consumer is that of 100 lbs. 

 live weight of an animal shpaed like the Suffolk lamb four days old 

 the butcher can hang up as carcase in his shop 53 lbs., and the cus- 



