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FOSSIL REPTILIA OF THE 



in number, never coalesce, but retain their primitive distinctness throughout life. The 

 sole ground taken to bridge over this significant difference in the structure of leg and foot 

 in the Bird and Dinosaur is to affirm that the distal epiphysis, pt, of the tibia in the Bird 

 is the homologue of the astragalus in the Mammal and Reptile (Fig. 16, a). 1 



" If the whole hind-quarters, from the ilium to the toes, of a half-hatched Chicken 

 could be suddenly enlarged, ossified, and fossilised as they are," 2 the ilium would be 

 distinguished from that of a Dinosaur by the major number of its sacrovertebral attach- 

 ments and by their greater extent, by the absence of the ridge continued from the super- 

 acetabular plate upon the antacetabular one ; the pelvis would be distinguished by the 

 presence in the ischium of an obturator process wanting in the Dinosaur (Fig. 12, is), and 

 by the absence of a pectineal process of the pubis present in the Dinosaur (ib., pb), by 

 the parallelism of the ischium and pubis, and by the backward extension of both bones 

 (compare Figs. 12 and 14). The differences grow and multiply as the comparison proceeds ; 

 as, e.g., by the non-extension, in the Chick, of the fibula (Fig. 14,/6) to the ankle-joint and 

 by the larger and more complex distal epiphysis of its tibia (Fig. 16, Dinornis), by the 

 absence of a tarsus, by the backward direction of the innermost or first toe (Fig. 16,«), as con- 

 trasted with the parallel position of that toe with the second toe in the reptilian foot (Fig. 16, 

 Scelidosaurus, Varanus). If the entire skeleton of an immature Chick, Ostrich, or Moa were 

 enlarged, whether suddenly or gradually, to the dimensions of that of a Cetiosaur, and 

 were so ossified and fossilised, the characters of the dorsal vertebras, of the cervical ver- 

 tebras, of the skull, and the absence of an anterior pair of limbs with fore-paws organized 

 to be applied to the soil and take their share in the support and progression of a long 

 and bulky trunk and massive head as in the Dinosauria, would be decisive against the 

 reference of such imaginary gigantic Chick to any known representative of the Dinosaurian 

 order of Reptiles. But, to the Biologist who rejects the principle of adaptation of struc- 

 ture to function, the foregoing facts and conclusions will have no significance. 



By a modification of the hind-limbs the Bear, and by addition of a longer sacrum to 

 plantigrade feet the Ground-sloth, may assume a crouching bent-kneed attitude and hold 

 the fore -limbs free to grapple with a foe or a tree. 



Such is the plasticity of some mammalian structures that, by due training, a Bear, a 

 Dog, or a Monkey may be taught to dance and walk erect for a brief space. It may be 

 doubted whether a cold-blooded, small-brained Reptile could by any training be brought 

 to exemplify the mode of motion conceived in the quotation at p. 92. But that, like 

 the Chlamydosaur with its long-toed, wide-spread, hind feet, the huge Dinosaurs 

 might assume the fighting posture of the Bear, when occasion called them to wield 

 their carpal weapons, is conceivable without commission of physiological or anatomical 

 solecism. 



1 Prof. Huxley, ' Quarterly Journal Geol. Soc.,' vol.xxvi, p. 29. 



2 lb., loc. cit., p. 30. 



