608 BRITISH FOSSIL REPTILES. 



joint. Nothing of this exists iu Dinosauriau or other Reptiles. Still more special is the 

 modification in Birds by which the leg is united with the foot. No break in the column 

 charged with the sustaining function peculiar thereto in the Bird is allowed beyond the 

 absolute necessities of bending movements of such column when subserving locomotion. 



The tarsal segment is suppressed; the metatarsal segment {mt) is aggrandised, 

 lengthened out and confluently compacted; the metatarsals of three toes are welded into 

 one bone. 



The joint of the leg with this bone is closely and tenaciously trochlear, strictly 

 limiting the movements of the foot to one plane. The long and slender phalanges 

 stretch forward at right angles to the metatarsus, and diverge to form a suitable base for 

 the columns to which has been assigned such an unique task — so peculiar a work — as is 

 performed by the hind limbs on the feathered class. 



Certain Dinosaurs \vielded carpal spines and some Mammals bore tarsal ones. It 

 would be a3 germain on that ground to derive Chaiina or Palamedea from Ignaiiodoii or- 

 Omosaurus, as Platypus from Phasianus. 



AVbat are the known structures in Meyalosaurus, lyuanodon, and other Binomuria, 

 which, corresponding with those iu Birds, would justify the conclusion or suspicion that 

 the ischium and pubis, besides being long and slender, as they are demonstrated to be 

 in Omosaurus, were directed from their acetabular ends backward parallel to one another ? 

 It is certain that the ischium in Iguanodon had not the ' obturator ' process charac- 

 teristic of the same bone in Birds, and as certain that there must be a mistake about the 

 matter when the same is predicated of the pelvic bone, erroneously called ischium, in 

 the immature or small kind of Iguanodon which has been termed 'Hypsilojohodon ' in 

 ignorance of the true structure of the mandibular teeth. 



That the pelvic bones, truly homologous wdth ischia, were " united in a median 

 ventral symphysis,"* is most probable from the shape and surface of the somewhat 

 expanded distal extremities of the unquestionable ischia iu OmosaiirKs. But such union 

 does not exist in Birds. If it should be found in all Pinosauria, it is one of the majority 

 of characters in which that order differs from the class of Birds and agrees with its own 

 class, viz. the Reptiles. 



Of the comparatively few sacral vertebris in Dinosauria the ' costal portions of the trans- 

 verse processes' (plcurapophyses) abut chiefly against the part of the ilium contributing to the 

 cup to be upborne by the thigh-bone ; there arc no postacetabular abutments against other 

 parts of the ilia, or against the comparatively broad iscliia, as in Birds. In the latter pelvic 

 character we have again to quit the Reptilian class and to indicate the repetition of 

 it in certain bird-like Lissencephalous Mammals. t 



The augmentation of number of sacral vertebrae beyond that — two — in Crocodiles and 

 Lizards, whose bellies trail upon the ground or are but little raised therefrom by the out- 



* Hii.xley, ' Quarterly Journal Geol. Soc.,' vol. xxvi. 



t 'Anat. of Vertebrates,' ii, pp. 39/— 402, figs. 2(i3, 2G-4, 266—268. 



