2 REPtlLES AND BIRDS. 



their lungs, but respiration is much less active. " Although," remarks 

 Sir Rich. Owen, " the heart of Birds resembles in some particulars 

 that of Reptiles, the four cavities are as distinct as in the Mammalia, 

 but they are relatively stronger, their valvular mechanism is more 

 perfect, and the contractions of this organ are more forcible and 

 frequent in Birds, in accordance with their more extended respiration 

 and their more energetic muscular action." It is true, as Professor 

 Huxley informs us, that the pinion of a bird, which corresponds with 

 the human hand or the forepaw of a reptile, has three points represent- 

 ing three fingers : no reptile has so few.* The breast-bone of a bird 

 is converted into membrane bone : no such conversion takes place in 

 reptiles. The sacrum is formed by a number of caudal and dorsal 

 vertebrae. In Reptiles the organ is constituted by one or two sacral 

 vertebrae. 



In other respects the two classes present many obvious differences, 

 but these are more superficial than would be suspected at a first glance ; 

 and Professor Huxley believes that, structurally, " reptiles and birds 

 do really agree much more closely than birds with mammals, or 

 reptiles with amphibians."' 



While most existing birds differ thus widely from existing reptiles, 

 the cursorial or struthious genera, comprising the Ostrich, Nandu, 

 Emu, Cassowary, Apteryx, and the recently extinct Dinornis of New 

 Zealand, come nearer to the reptiles in structure. All of these are 

 remarkable for the shortness of their wings, the absence of a crest or 

 keel upon the breast, and peculiarities of the skull, which bring them 

 nearer to the Reptilian order. But the gap between Reptiles and Birds 

 is only slightly narrowed by these examples, and is somewhat unsatis- 

 factory to those who advocate the development theory, which asserts 

 that all animals have proceeded, by gradual modification, from a 

 common stock. 



Traces had been discovered in the Mesozoic formations of certain 

 ornitholites, which were too imperfect to determine the affinities ot 

 the bird. But the calcareous mud of the ancient sea-bottom, which 

 has hardened into the famous lithographic slate of Solenhofen, 

 revealed to Hermann von Meyer, in 1861, first the impression 

 of a feather, and, in the same year, the independent discovery 

 of a skeleton of the bird itself, which Von Meyer had named 

 Ardueopteryx lithograph! ta. This relic of a far-distant age now 

 adorns the British Museum (Fig. i). 



The skull of the Archaeopteryx is almost lost, but the leg, the foot, 



* Vide, however, p. 8. ED. 



