﻿KIMMERIDGE CLAY. 



81 



numerically ; and this concurs with the exceptional reduction of number in the ' dorsals ;' 

 both being in special physiological relation to bipedal support and progression. 



The numerous cervicals have peculiar joints, governing the sigmoid flexure and 

 oscillating sway of the long and slender neck ; whereby, in walking, both neck and head, 

 in Birds, may be brought more directly over the supporting columns of the hind limbs as 

 these change their position. These limbs, moreover, have their specialties in relation to 

 their peculiar work in the vertebrate series. 



The femur (Kg. 14 (Dinornis), f) is relatively short ; the tibia (t) relatively long ; the 

 fibula (fb), styliform and short, takes no share in the ankle-joint, but co-operates with the 

 tibia in a special manner to extend and strengthen the articulation of the leg with the thigh. 

 The femoral condyles are concomitantly modified to effect the accessory femoro-fibular 

 joint. Nothing of this exists in Dinosaurian 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 loco- 

 motion. 



The tarsal segment is suppressed; the metatarsal segment (mi) is aggrandised, 

 lengthened out and con fluently 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 wielded carpal spines and some Mammals bore tarsal ones, it 

 would be as germain on that ground to derive Chauna or Palamedea from Iguanodon or 

 Omosaurus, as Platypus from Phasianus. 



"What are the known structures in Megalosaurus, Iguanodon, and other Dinosauria, 

 which, corresponding with those in 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 ' Hypsilophodon ' in 

 ignorance of the true structure of the mandibular teeth. 



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

 ventral symphysis/' 1 is most probable from the shape and surface of the somewhat 



1 Huxley, 1 Quarterly Journal Geol. Soc.,' vol. xxvi. 



