8 
JOURNAL OF MAMMALOGY 
PRINCIPLES AND NOMENCLATURE OF PROPORTION CHARACTERS 
I have recently pointed out that in mammals the larger percen- 
tage of the characters employed in specific and subspecific description 
are proportion characters and color intensity characters. The remaining 
smaller percentage are new characters or presence and absence characters 
(see Miller’s “Mammals of Western Europe”)- 
As a beginning, we mammalogists might adopt one system of obser- 
vation and description in the matter of the proportions of the skeleton 
and of the skull and unify the different modes of description which 
prevail at present as, for example, in Miller’s “Mammals of Western 
Europe,” in Merriam’s recent studies of the bears of North America,^^ 
in researches on limbs and skulls of ungulates of Osborn, and in the 
craniology introduced by Osborn of the horse and of the titanotheres. 
In respect to limb proportion also, recent discoveries by Osborn and 
Gregory among the ungulates show that the very precise proportions 
expressed by indices and ratios enable us to divide the ungulates into 
ambulatory, submediportal, mediportal, and graviportal types, and 
into cursorial and subcursorial types. These are convergent or homo- 
iplastic types quite irrespective of ancestry. For example, a horse and 
an antelope, capable of carrying the same body weight at the same 
speed, exhibit exactly similar indices and ratios in their limbs. These 
similar proportions are adaptations to speed and weight which evolve 
quite irrespective of family lines. 
SIX DIVERSE CAUSES OF VARIATION 
Another principle of skeletal proportion also requires reconsidera- 
tion from the standpoint of the newer biological studies enumerated by 
Osborn in his recent work, “The Origin and Evolution of Life,” in 
which the close relation of the proportions of various parts of the body 
to the internal secretions of the endocrine glands is demonstrated. 
The principal endocrine glands are the interstitial (sex), the thyroid, 
the thymus, the pituitary, the suprarenal, the pineal; all are now 
known to influence growth and development. For example, the pro- 
portion of the pelvis in the horse has a direct relation to the secretion 
of the interstitial tissues of the sex glands; a stallion pelvis has different 
proportions from that of a gelding, as well as from that of a mare. 
23 Merriam, C. H. Review of ‘the Grizzly and Big Brown Bears of North 
America. North American Fauna, no. 41. 1918. 
