Prof. Huxley on the Animals between Birds and Reptiles. 71 
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 forma- 
tions, 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 Pterodactyles, 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 praemaxille 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 reptiles as well as in birds ; 
the structure of the scapulo-coracoid 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 pro- 
longed, in total contrast to the abortion of the corresponding digit in 
birds. The pelvis is as wholly unlike that of birds as is the hind 
limb and foot. 
Thus it appears that Pterodactyles, among reptiles, approach birds 
much as Bats, among mammals, may be said to do so. They area 
sort of reptilian Bats * rather than links between reptiles and birds ; 
and it is precisely in those organs which in birds are the most cha- 
racteristically ornithic, the manus and the pes, that they depart most 
widely from the ornithic type. 
Clearly, then, the passage from reptiles to birds is not from the 
flying reptile to the flying bird. Let us try another line. I have 
already observed that in the existing world the nearest approxima- 
tion to reptiles 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 reptiles which approached these flight- 
less 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. 
The Dinosauria, a group of extinct reptiles, containing the genera 
Iguanodon, Hadrosaurus, Megalosaurus, Poikilopleuron, Scelidosaurus, 
Plateosaurus, &c., which occur throughout the whole series of the Me- 
sozoic rocks, and are, for the most part, of gigantic size, appear to me 
to furnish the required conditions. 
In none of these animals is the skull or the cervical region of 
* Tt will be understood that I do not suggest any direct affinity between 
Pterodactyles and Bats. 
