﻿KIMMERIDGE CLAY. 



85 



it; the tibia alone (woodcut, Fig. 16, t) articulating with the metatarsus, ib., mt, by a 

 finely fashioned, close-fitting, interlocking joint. 



As in all warm-blooded quadrupeds and the majority of cold-blooded ones, recent and 

 extinct, the articular ends of the tibia are ossified independently of the shaft, are in the 

 condition of epiphyses in the young Bird (Fig. 16, Dinornis, P t), and retain longer that con- 

 dition in the Reptile (Fig. 16, Varanus, p t, and Scelidosaurus, p t). The attachment of the 

 distal epiphysis with the shaft of the tibia (t) is made firmer in the biped (Dinornis, p t) 

 than in the quadruped (Fig. 16, Ruminant, p t) ; and the extent of the attachment is greater, 

 is more irregular or interlocking in the warm-blooded quadruped than in the cold-blooded 

 one ; it is still greater in the Bird, in which a process ascends upon the front of the 

 diaphysis, closely fitting to a groove there, and clamping, as it were, the articular 

 epiphysis to the main shaft of the leg bone. The bigger the Bird the greater the share 

 of locomotion allotted to the hind pair of limbs in standing, walking, or running, the 

 longer is the clamping process and the later is the period of the coalescence of the 

 epiphysis with the shaft. The Ostrich among existing Cursores, and the Dinornis amongst 

 extinct ones exemplify this relation. In the metatarsus of the Bird the shafts of the ento-, 

 meso-, and ecto-metatarsi are severally ossified from separate centres, but the proximal 

 epiphyses of the three bones are ossified from one centre, and form a single cap of bone 

 where the shafts are still distinct. 1 Such cap (Fig. 16, Dinornis, p m ) may be arbitrarily 

 homologised with one or more bones of the distal tarsal series in Reptiles (Fig. 16, Scelido- 

 saurus, b, e ; in Varanus, b,e) and in Mammals (Fig. 16, Ruminant, b, n, e). It seems more 

 natural to regard it as answering to the epiphysial cap, covering the ends of the two chief 

 metatarsals, of the Ruminant (ib. ib., pm, Hi, iv), and I associate such instances of complex 

 osteogeny of the metatarsus with the high conditions of organisation differentiating the 

 warm-blooded classes, Aves and Mammalia, from the cold-blood Beptilia. 



In the Ruminant, as in the Bird, the single epiphysis and multiple diaphyses coalesce 

 into one so-called ' cannon bone.' 



In the Dinosauria the hind limbs are not adapted, as in the Birds, for transference 

 of the entire weight of trunk, neck, head, and fore limbs, from the leg upon the foot by due 

 development and modifications of the main leg-bone, the tibia ; but the fibula is continued 

 to the ankle-joint, and takes a larger share in its formation than is usual in Mammals. 

 Both leg-bones have their distal epiphyses (Fig. 16, p/, p t. Scelidosaurus, Varanus). The 

 tarsal segment is represented, usually by four ossicles : 2 one, a, answers, by its connections, 

 to the astragalus, naviculare, and entocuneiform bones of the Mammal ; a second, I, repre- 

 sents the calcaneum with the lever process slightly if at all developed ; there are, also, a 

 cuboid, h, and an ectocuneiform, e . The metatarsals, whether they be three or four 



1 'Transactions of the Zoological Society of London,' 4to, vol. iv (1856), p. 149, pi. xlv (Dinornis 

 elephantopus, pullus ; Dinornis crassus, pullus). 



2 Palaeont. vol. for I860, Oolitic Reptilia (Scelidosaurus), tab.xi, figs. 2, 3, 4, Scelidosaurus, Varanus, 

 Crocodilus. 



