FOSSIL VERTEBRATES — REPTILIA 721 
in the air. Just as the preceding groups, the Jcthyosaurs and the 
Flestosaurs had been compelled by the great struggle between 
the large number of reptilian forms to seek some peculiar modes 
of life to maintain an existence and had taken to the water, so 
these forms had been compelled to seek new environment and 
became adapted to an aérial, or partially aérial, life. Whether 
they were possessed of any great power of flight or were only 
capable of soaring, as the flying-squirrel, is not known, but the 
enormous distance that their remains are found from what must 
have been the land at the time and the pneumaticity of their 
bones speak for a very well developed power of flight. There 
was great variation in the sizes of the animals, some being very 
small, while others reached a spread of 18 feet from tip to tip of 
the expanded wings. The bones were all hollow and provided 
with foramina at the extremities that seem to have filled the 
same function that the foramina in the bones of the birds do, 
that of supplying air to the interior of the bones. These two 
facts seem to imply that the Pterodactyls were warm-blooded, 
but this can not, of course be definitely settled from the skele- 
ton. The tail was either long or short. In the cases where it 
was long, it ended in an expansion that served as a rudder to 
guide the flight of the animal. The fore limbs were very much 
longer than the hind limbs and were especially modified to sup- 
port the organ of flight. This was a strong membrane much 
like that which serves the same purpose in the bats. In certain 
of the specimens preserved in the fine grained slates of the 
Solenhofen beds, the folds of the wings are preserved and even 
the course of the nutrient arteries may be followed. There 
were four digits on the front foot or wing, the last four, and the 
last of these, or the little finger, was enormously extended so 
that it was many times the length of the arm. The other fingers 
were short and greatly reduced in size ; they ended in small 
claws which perhaps aided the animal to cling to the sides of the 
cliffs on which it lived. The wing membrane stretched from 
this extended finger and the arm to the weak posterior limbs. 
In all probability the membrane extended also between the 
