42 THE AMERICAN BISONS. 
between two individuals of the same species. A comparison of the anterior 
and posterior limbs gives a similar result. Thus the proportionate length 
of the fore limb (excluding the scapula) to the hind limb, in the American 
bison, is the same as that in the aurochs, namely, as 91 to 100. 
While the skeleton of the aurochs is, generally speaking, heavier and more 
massive than that of the American bison, and considerably larger in all its 
measurements, the ribs are actually much shorter and straighter, giving a 
much smaller thoracic cavity. The length of the first mb in B. americanus, for 
example, is 452 mm.; in B. bonasus, 375 mm.; of the third rib in B. ameri- 
canus, 548; in B. bonasus, 492°; of the sixth ribin B. americanus, 711; in B. 
bonasus, 697; of the ninth rib in B. americanus, 910; in B. bonasus, 869; of 
the twelfth rib in B. americanus, 783; in B. bonasus, 750; of the fourteenth 
rib (osseous portion only), in B. americanus, 437; in B. bonasus, 418. The 
pelvis, on the other hand, is fully one fourth larger in all its dimensions, and 
the bones that enter into its composition are far more massive in the aurochs 
than in the American bison. The smaller size of the posterior part of the 
vertebral column in the American bison is also further seen in its diminutive 
tail as compared with that of the aurochs. Among other noticeable skeletal 
differences are the relatively greater length of the dorsal series of the ver- 
tebree, and shorter sternum of the American bison. 
While the above-given comparisons are based on a single skeleton of each 
species, the subjoined measurements (see Table IX) shows that these con- 
clusions are borne out by further material. 
As already noticed (p. 2), the American bison is not distinguished from 
the aurochs by the possession of fifteen pairs of ribs and only four lumbar 
vertebra, as was formerly supposed, and as has been so often stated, the two 
species having normally the same number of lumbar vertebrae and the same 
number of pairs of ribs. Professor Riitimeyer* refers to the greater length of 
the anterior dorsal spines in Bison americanus, but this difference is evidently 
not constant, as is shown by the measurements given in Table IX. | He also 
regards the differences in the relative length of the different segments of 
the extremities to each other and to the whole height of the animal as 
affording differences worthy of note. He gives a table illustrative of these 
differences, which I subjoin. . He says: “Nahm ich die Large von Metacar- 
pus und Carpus zusammen als Einheit, so verhielten sich dazu die andern 
Segmente der Extremititen folgendermassen : — 
* Versuch einer natiirlichen Geschichte des Rindes, ete., Part II, p. 68. 
nce nove 
