XVI] IN THE SKELETON OF QUADRUPEDS 707 



though comparatively small, are obviously fashioned for support, 

 but the weight which they have to carry is far less than that 

 which the hind-limbs bear. The head is small and the neck 

 short, while on the other hand the hind- quarters and the tail are 

 big and massive. The backbone bends into a great, double-armed 

 cantilever, culminating over the pelvis and the hind-limbs, and 

 here furnished with its highest and strongest spines to separate 

 the tension-member from the compression-member of the girder. 

 The fore-legs form a secondary supporting pier to this great 

 cantilever, the greater part of whose weight is poised upon the 

 hind-limbs alone. 



Fig. 350. Diagram of Stegosaurus. 



(6) In a bird, such as an ostrich or a common fowl, the 

 bipedal habit necessitates the balancing of the load upon a single 

 double-armed cantilever-girder, just as in the Iguanodon and the 

 kangaroo, but the construction is effected in a somewhat different 

 way. The great heavy tail has entirely disappeared ; but, though 

 from the skeleton alone it would seem that nearly all the bulk of 

 the animal lay in front of the hind-limbs, yet in the living bird 

 we can easily perceive that the great weight of the abdominal 

 organs lies suspended behind the socket for the thigh-bone, and 

 so hangs from the posterior lever-arm of the cantilever, balancing 

 the head and neck and thorax whose combined weight hangs from 



Tornier, SB. Ges. Naturf. Fr. Berlin, pp. 193-209, 1909; Hay, 0. P., Amer. Nat. 

 Oct. 1908; Tr. Wash. Acad. Sci. xlii, pp. 1-25, 1910; Holland, Anj,er. Nai. May, 

 1910, pp. 259-283; Matthew, ibid. pp. 547-560; Gilmore, C. W. (Restoration of 

 Stegosaurus). Pr. U.S. Nat. Museum, 1915. 



45—2 



