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 rib in B. amcricanns, for 

 example, is 452 mm.; in B. bonasus, 375 mm.; of the third rib in B. amcri- 

 canus, 548 ; in B. bonasus, 492 ; of the sixth rib in B. americamis, 711 ; in B. 

 bonasus, 697; of the ninth rib in B. americamis, 910; in B. bonasus, 869; of 

 the twelfth rib in B. americamis, 783; in B. bonasus, 750; of the fourteenth 

 rib (osseous portion only), in B. americanus, 437 ; in B. bonasus, 41S. 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- 

 tebra 1 , and shorter sternum of the American bison. 



While the above-given comparisons are based on a single skeleton of each 

 species, the subjoined measurements (sec Table IX i shows that these con- 

 clusions arc borne out by further material. 



A- already noticed (p. 2), the American bison is not distinguished from 

 tin' 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 sane number of lumbar vertebrae and the same 

 number of pairs of ribs. Professor Rutimeyer* refers to the greater length of 

 tin- anterior dorsal spines in Bison americamis, but this difference is evidently 

 nut constant, as is shown by the measurements given in Table IX. lie also 

 regards the differences in the relative length of the different segments of 



the extremities to each other and to the whole height of tlie animal as 



affording differences worthy of note, lie gives a table illustrative of these 

 differences, which I subjoin. Be says: "Nahm ich die Large von Metacar- 

 pus Mid Carpus ziisanitneu als Kinheit. so \erliielten sich da/ii die andern 



lente der Extremitaten folgendermassen : — 



• \ . i m li . in. i ii. mull. In ii (.. -. In. Iii. .1. - Hindi . cb . Part II. p 68 



