2 REPTILES AND BIRDS. 
their lungs, but respiration is much less active. ‘“ Although,” remarks 
Professor 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 ofa 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 
vertebree. In Reptiles the organ is constituted by one or two sacral 
vertebree. , 
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, Nandou, 
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 
Archaeopteryx lithographicus. This relic of a far-distant age now 
adorns the British Museum. 
The skull of the Archzeopteryx is almost lost, but the leg, the foot, 
* Vide, however, p. 8.— ED. 
