THE FORE LIMBS. 89 



The Humerus. 

 (Plate XXVIII; and woodcuts 106-107, below.) 



The luinierus of DiitocriKs is a .strong' bone, pre.senting roughened and 

 tuberculated surfaces, evidently for the attachment of powerful muscles. 

 In this respect, it is in strong contrast with the comparatively smooth 

 femur, and a glance at the structure of the skeleton, as shown in the 

 restorations in Plates LV and LVI, will suggest a reason for tliis 

 difference. 



The hind leg of Dinoccras, like that of the elephant, could be 

 straightened, so that the weight of the hinder part of the body was 

 supported by a vertical column of bones, rising from the ankle joint to the 

 pelvis, and comparatively little muscular action was required to keep the 

 bones in the requisite position. Tlie elbow joint, on the contrary, was not 

 capable of sufficient extension to bring the radius and ulna into a line 

 with the humerus, but the weight of the fore ])art of the Ijody was 

 supported, as in ordinary quadrupeds, by a long column with more or less 

 flexure near the middle. Constant muscular action was therefore necessary 

 to sustain the weight of tliis part of the body. The heav\- and strongly 

 armed head added still more to the muscular efforts recjuircd of the fore 

 limbs, during progression, or even while standing at rest. 



The proximal end of the humerus (Plate XXVIII, figure 3,rt) presents 

 a large rounded articular face, or head, moi'e convex antero-posteriorly 

 than from side to side. The axis of the head of the humerus forms an 

 angle of nearly 30° with that of the shaft. This angle, while greater than 

 that seen in the same bone of the elephant, is much less than in most 

 quadrupeds. 



The great tuberosity of the humerus is prominent, but not elevated, 

 and is separated, by a shallow and narrow bicipital groove, from the low 

 lesser tuberosity. The great tuberosity is about as large as in the 

 elephant, but does not extend so high, not rising to the head of the 

 humerus. It is stiongly tuberculated and roughened, and is continued 

 down the anterior and outer part of the shaft into a prominent ridge below 



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