H. F. OSBORN — MAMMALIAN PALÆONTOLOGY 89 
nocerotoidea. Divergence by the above factors has long been recognized. 
There are also to be seen phyletie series combining in various ways either 
of the following eight conditions of foot, skull and tooth structure, which 
are not found to be necessarily correlated : 
Primitive Condition. : Secondary Condition. 
{ (6) Elongation (dolichocephaly) of skull 
PNA Ü (7) Abbreviation (brachycephaly) » » 
2 , ( (9) Elongation (dolichopody) of limbs 
(8) Mesatipody | (10) Abbreviation(brachypody) »  » 
(11) Brachyodonty | (12) Elongation (hypsodonty) of teeth 
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 res- 
tated as follows! : The feet (correlated chiefly with limb and body 
structure) and the teeth (correlated chiefly with skull and 
neck structure) diverge independently in adaptation respec- 
tivelytosecuring(feet)andearing(teeth)foodunderdifferent 
conditions; each evolvesdirectly for its own mechanical func- 
tions or purposes, yet in suchamannerthateach subservesthe 
other. Thus, for example, there is a frequent correlation between doli- 
chocephaly, dolichopody and hypsodonty, as in certain of the Equide ; 
but there are so many exceptions to such correlation, because of the 
separate adaptive evolution ofeach organ, that it would be enti- 
rely 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 important advances of 
the past decade, for which the way was largely prepared, in the previous 
decade, by Scorr’s papers on Oreodon, Poëbrotherium and Mesohippus, 
has been the clear recognition of this law. These phenomena give rise to 
an enormous number of analogies (homoplasies, parallelisms, conver- 
gences) not onlv of structure but of entire types, of families, and of 
groups, very confusing to the seeker of real phyletic relationship. 
Evolution in part determinate. — As regards the modes and factors 
of evolution ?, the continuous stages of evolution which we are securing 
among the horses, camels, rhinoceroses, and many other families, afford 
opportunities which have never been afforded before. We are with adap- 
! Osporn. Amer. Nat. XXXVI, 1902, p. 365. 
? Scorr, W. B. On the Mode of Evolution in the Mammalia and on some of the 
Factors in the Evolution of the Mammalia. Jour. Morphol. Vol. v, 1891, No. 3, 
pp. 361-378, 378-402. 
