XVI] COMPARATIVE ANATOMY OF BRIDGES 993 



obvious that the two piers of the bridge, that is to say the fore-legs 

 and the hind-legs, do not bear (as they do in the Forth Bridge) 

 separate and independent loads, but the whole system forms a 

 continuous structure. In this case, the calculation of the loads 

 will be a little more difficult and the corresponding design of the 

 structure a Httle more complicated. We shall accordingly simplify 

 our problem very considerably if, to begin with, we look upon the 

 quadrupedal skeleton as constituted of two separate systems, that 

 is to say of two balanced cantilevers, one supported on the fore-legs 

 and the other on the hind; and we may deal afterwards with the 

 fact that these two cantilevers are not independent, but are bound 

 up in one common field of force and plan of construction. 



In both horse and ox it is plain that the two cantilever systems 

 into which we may thus analyse the quadrupedal bridge are unequal 

 in magnitude and importance. The fore-part of the animal is much 

 bulkier than its hind-quarters, and the fact that the fore-legs carry, 

 as they so evidently do, a greater weight than the hind-legs has 

 long been known and is easily proved ; we have only to walk a horse 

 on to a weigh-bridge, weigh fijst his fore-legs and then his hind-legs, 

 to discover that what we may call his front half weighs a good deal 

 more than what is carried on his hind feet, say about three-fifths 

 of the whole weight of the animal. 



The great (or anterior) cantilever then, in the horse, is constituted 

 by the heavy head and still heavier neck on one- side of that pier 

 which is represented by the fore-legs, and by the dorsal vertebrae 

 carrying a large part of the weight of the trunk upon the other 

 side; and this weight is so balanced over the fore-legs that the 

 cantilever, while "anchored" to the other parts of the structure, 

 transmits but little of its weight to the hind-legs, and the amount 

 so transmitted will vary with the attitude of tne head and with 

 the position of any artificial load*. Under certain conditions, as 

 when the head is thrust well forward, it is evident that the hind-legs 

 will be actually relieved of a portion of the comparatively small 

 load which is their normal share. 



* When the jockey, crouches over the neck of his race-horse, and when Tod 

 Sloan introduced the "American seat," the avowed object in both cases is to relieve 

 the hind-legs of weight, and so leave them free for the work of propulsion. On 

 the share taken by the hind-limbs in this latter duty, and other matters, cf. 

 Stillman, The. Tlnrne, in Motion, 1882, p. 69. 



