362 
Journal of Agricultural Research 
Vol. VII, No. 8 
(Sondenfjeldske). These mares are all measured in the same way, and 
the measurements are registered in the stud book. The measurement is 
taken near the middle of the cannon bone, at its narrowest point. In 
the data the writer found five mares whose dams were 1 year old at the 
time of service. Both because this number is too small to give average 
values whose significance can be estimated, and because of the abnormal 
character of these extremely young dams, they have been excluded in 
the general treatment of the problem. Two other mares are excluded, one 
for the reason that the writer knows that her cannon bone is abnormally 
thickened, and the other because the measurement of the side breadth 
is abnormally small compared with the circumference. 
Along with age, there are other causes that have an influence on the 
size of the cannon bone of the offspring. Heredity is the first of these 
causes to be considered, because it is probably of great importance in 
this particular investigation, since the modem Gudbrandsdal horses 
include blood lines that represent a cross between the original horse 
type of eastern Norway (the most northern branch of the occidental 
horse) and different light-horse types. In the seventeenth and eight¬ 
eenth centuries there were imported into Norway stallions of the Fred- 
ricsborgian horse or a closely related type. The Fredricsborgian horse 
was a light-horse type that descended from crosses of Seeland country 
horses, Spanish, and oriental horses. In the nineteenth century there 
was imported into Norway an English thoroughbred stallion, Odin. 
This stallion became by chance the founder of one of the most impor¬ 
tant stallion lines of the Gudbrandsdal breed. In the nineteenth century 
the blood of the other Norwegian breed, the Fjord horse, was mixed 
with the Gudbrandsdal horse by the use of several mares, and thus be¬ 
came an influence on the latter breed (12, 13). If cannon-bone size is 
inherited, it is perfectly clear that the Gudbrandsdal horse is not a pure¬ 
bred in a genetic sense, since extreme heterozygosis must result from 
the numerous infusions of blood from such diverse sources. 
One should consider the influence of nourishment on the size of the 
cannon bone, but the number of individuals in this investigation is so 
large and the conditions of nourishment are such that the effects of 
different nourishments would probably eliminate each other, or at least 
would be insignificant. Although nutrition undoubtedly has a pro¬ 
nounced effect upon size and growth, the writer has assumed that 
under good conditions the adult size of the cannon bone represents in 
a fair way the inherent possibilities of an animal. Such has been the 
usual assumption in genetic investigations of size characters. 
The first task was to calculate the correlation between the age of 
the sires and the size of the cannon bone of female offspring. Table I 
gives the number and kinds of mares sired by stallions of different 
ages. Measurements under 18 cm. and over 21 cm. are arranged in 
the subclass headed 18 and 21, respectively. The averages of arrays 
