704 ON FORM AND MECHANICAL EFFICIENCY [ch. 



require to weigh the total load, not in two portions, but in many ; 

 and we should also have to take close account of the general form 

 of the animal, of the relation between that form and the distribu- 

 tion of the load, and of the actual directions of each bone and 

 ligament by which the forces of compression and tension were 

 transmitted. All this lies beyond us for the present; but never- 

 theless we may consider, very briefly, the principal cases involved 

 in our enquiry, of which the above animals form only a partial 

 and preliminary illustration. 



(1) Wherever we have a heavily loaded anterior cantilever 

 arm, that is to say whenever the head and neck represent a 

 considerable fraction of the whole weight of the body, we tend 

 to have large bending-moments over the fore-legs, and corre- 

 spondingly high spines over the vertebrae of the withers. This 



Tail 



Head 



Fig. 349. Stress-diagram of Titanotherium. 



is the case in the great majority of four-footed, terrestrial animals, 

 the chief exceptions being found in animals with comparatively 

 small heads but large and heavy tails, such as the anteaters or 

 the Dinosaurian reptiles, and also (very naturally) in animals 

 such as the crocodile, where the "bridge" can scarcely be said 

 to be developed, for the long heavy body sags down to rest upon 

 the ground. The case is sufficiently exemplified by the horse, 

 and still more notably by the stag, the ox, or the pig. It is 

 illustrated 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 large; 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 



