(5) Mesaticephaly 
(8) Mesatipody 
202 The American Geologist. October. 1905 
skull and tooth structure, which are not found to be neces- 
sarily correlated: 
Primitive Condition. Secondary Condition. 
(6) Elongation (dolichocephaly) 
of skull 
(7) Abbreviation (brachyceph- 
aly) of skull 
(9) Elongation (dolichopody) of 
limbs 
(10) Abbreviation (brachypody 
of limbs 
„ , (12) Elongation (hvpsodontv) of 
(11) Brachyodonty <J q ° . Ji 
Law of correlation. — The bearing of these observations 
on Cuvier's law of correlation is to modify rather than to 
displace it. It may be restated as follows 1 : The feet (cor- 
related chiefly with limb and body structure) and the teeth 
(correlated chiefly with skull and neck structure) diverge 
independently in adaptation respectively to securing (feet) 
and eating (teeth) food under different conditions ; each 
evolves directly for its own mechanical functions or pur- 
poses, yet in such a manner that each subserves the other. 
Thus, for example, there is a frequent correlation between 
dolichocephaly, dolichopody and hypsodonty, as in certain 
of the Equidaej but there are so many exceptions to such 
correlation, because of the separate adaptive evolution of 
each organ, that it would be entirely impossible to predict 
the structure of the tooth from the structure of the claw, 
or vice versa. 
Law of analogous evolution. — One of the most impor- 
tant advances of the past decade, for which the way was 
largely prepared, in the previous decade, by Scott's papers 
on Oreodon, Poebrotherium and Mesohippus, has been the 
clear recognition of this law. These phenomena give rise to 
an enormous number of analogies (homoplasies, parallel- 
isms, convergences) not only of structure but of entire 
types, of families, and of groups, very confusing to the 
seeker of real phyletic relationship. 
1 Osborn. Amer. Nat. xxxvi, 1902, p. 363. 
