1004 ON FORM AND MECHANICAL EFFICIENCY [ch. 



in the accompanying diagram of the conditions in the great extinct 

 Titanotherium. 



(2) In the elephant and the camel we have similar conditions, 

 but slightly modified. In both cases, and especially in the latter, 

 the weight on the fore-quarters is relatively krge ; and in both cases 

 the bending-moments are all the larger, by reason of the length 

 and forward extension of the camel's neck and the forward position 

 of the heavy tusks of the elephant. In both cases the dorsal spines 

 are large, but they do not strike us as exceptionally so; but in 

 both cases, and especially in the elephant, they slope backwards 

 in a marked degree. Each spine, as already explained, must in all 

 cases assume the position of the diagonal in the parallelogram of 

 forces defined by the tensions acting on it at its extremity; for it 

 constitutes a "hinged lever," by which the bending-moments on 

 either side are automatically balanced ; and it is plain that the more 

 the spine slopes backwards the more it indicates a relatively large 

 strain thrown upon the great ligament of the neck, and a relief 

 of strain upon the more directly acting, but weaker, Hgaments of 

 the back and loins. In both cases, the bending-moments . would 

 seem to be more evenly distributed over the region of the back than, 

 for instance, in the stag, with its light hind-quarters and heavy load 

 of antlers: and in bo^h cases the high "girder" is considerably 

 prolonged, by an extension of the tall spines backwards in the 

 direction of the loins. When we come to such a case as the mam- 

 moth, with its immensely heavy and immensely elongated tusks, 

 we perceive at once that the bending-moments over the fore-legs 

 are now very severe; and we see also that the dorsal spines in this 

 region are. much more conspicuously elevated than in the ordinary 

 elephant. 



(3) In the case of the giraffe we have, without doubt, a very 

 heavy load upon the fore-legs, though no weighings are at hand 

 to define the ratio; but as far as possible this disproportionate 

 load would seem to be relieved by help of a downward as well as 

 backward thrust, through the sloping back to the unusually low 

 hind-quarters. The dorsal spines of the vertebrae are very high 

 and strong, and the whole girder-system very perfectly formed. The 

 elevated rather than protruding position of the head lessens the 

 anterior bending-moment as far as possible, but it leads to a strong 



