ON ANIMALS BETWEEN BIRDS AND REPTILES. 
239 
animal Evolution, I am able to show a considerable piece of 
parchment evidently belonging to them. 
To superficial observation no two groups of beings can appear 
to be more entirely dissimilar than Eeptiles and Birds. Placed 
side by side, a Humming-bird and a Tortoise, an Ostrich and a 
Crocodile, ofier the strongest contrast, and a Stork seems to have 
little but animality in common with the Snake it swallows. 
Careful investigation has shown, indeed, that these obvious 
differences are of a much more superficial character than might 
have been suspected, and that Eeptiles and Birds do really agree 
much more closely than Birds with Mammals, or Eeptiles with 
Amphibians. But still, though not as wide as a church-door 
or as deep as a well,” the gap between the two groups, in the 
present world, is considerable enough. 
Without attempting to plunge into the depths of anatomy, 
and confining myself to that osseous system to which those 
who desire to compare extinct with living animals are almost 
entirely restricted, I may mention the following as the most 
important differences betvv^een all the Birds and Eeptiles which 
at present exist. 
1. The pinion of a Bird, which answers to the hand of a man 
or to the forepaw of a Eeptile, contains neither more nor fewer 
than three fingers. These answer to the thumb and the two 
succeeding fingers in man, and have their metacarpals connected 
together by firm bony union, or, in other words, are ankylosed. 
Claws are developed upon the ends of at most two of the three 
fingers (that answering to the thumb and the next), and are 
sometimes entirely absent (Plate XXVII. fig. 2). No Eeptile 
with well-developed forelimbs has so few as three fingers ; nor 
are the metacarpal bones of these ever united together ; nor 
do they (Plate XXVII. fig. 1) present fewer than three claws at 
their terminations (with the exception of the marine chelonia). 
2. The breast-bone of a Bird becomes converted into a mem- 
brane-bone, and ossification commences in it from at least two 
centres. The breast-bone of no Eeptile becomes converted into 
membrane-bone, nor does it ever ossify from several distinct 
centres. 
3. A considerable number of caudal and lumbar, or dorsal, 
vertebrae unite together with the proper sacral vertebrae of a Bird 
to form its sacrum.” In Eeptiles the same region of the spine 
is constituted b}^ the one or two sacral vertebrae. 
4. In Birds the haunch-bone (ilium) extends far in front of, 
as well as behind, the acetabulum ; the ischia and pubes are 
directed backwards, almost parallel with it and with one another ; 
and the ischia do not unite in the ventral middle line of the 
body (Plate XXVII. fig. 4). In Eeptiles, on the contrary, the 
