242 
POPULAR SCIENCE REYIEW. 
disunited. Thus it is a matter of fact that, in certain particulars, 
the oldest known bird does exhibit a closer approximation to 
reptilian structure than any modern bird. 
Are any fossil reptiles more bird-like than those which now 
exist ? As in the case of birds, the Tertiary formations yield 
no trace of reptiles which depart from the type of the existing^ 
groups. But, otherwise than is true of birds, the newest of the 
Mesozoic formations, the Chalk, makes us acquainted with 
reptiles, which, at first sight, seem to approach birds in a very 
marked manner. These are those flying reptiles, the Ptero- 
dactyles, which resemble the great majority of birds in the 
presence of air-cavities in their bones, in the wonderfully bird- 
like aspect of their coracoid and scapula, and in their broad 
sternum with its median crest. Furthermore, in some of the 
Pterodactyles, the premaxillse and the symphysial part of the 
mandibles were prolonged into beaks, which appear to have been 
sheathed in horn, while the rest of each jaw was armed with 
teeth. But horn-sheathed beaks are found in living chelonian 
reptiles as well as in birds ; the structure of the scapulocoracoid 
arch and of the sternum, and the pneumaticity of the bones, 
vary greatly among birds themselves ; and these characters of 
the Pterodactyles may be merely adaptive modifications. On 
the other hand, the manus has four free digits, the three inner 
of which are strongly clawed, while the fourth is enormously 
prolonged, in total contrast to the abortion of the corresponding 
digit in birds. The pelvis is as wholly unlike that of birds as 
are the hind-limb and foot. 
Thus it appears that Pterodactyles, among Eeptiles, approach 
birds much as Bats, among Mammals, may be said to do so. 
They are a sort of reptilian Bats * rather than liuks between 
Eeptiles and Birds, and it is precisely in those organs, the manus 
and the pes, which, in birds, are the most characteristically 
ornithic, that they depart most widely from the ornithic type. 
Clearly, then, the passage from Eeptiles to Birds is not from the 
flying Eeptile to the flying Bird. Let us try another line. I 
have already observed that, in the existing world, the nearest 
approximation to Eeptiles is presented by certain land Birds, 
the Ostriches and their allies, all of which are devoid of the 
power of flight by reason of the small relative size of their 
fore limbs and of the character of their feathers. Can we find 
any extinct Eeptiles which approached these flightless birds, not 
merely in the weakness of their fore limbs, but in other and more 
important characters ? I imagine that we can, if we cast our 
eyes in what, at first sight, seems to be a most unlikely direction. 
* It will be understood that I do not suggest any direct aflhiity between 
Pterodactyles and Bats. 
