THE MASTERY OF THE AIR 257 
adaptations for flight have been wrought out in 
the bodies of bird and bat. Both are lightly 
built as regards their skeleton, which means a 
big surface for fastening muscles on to, with- 
out great increase in weight. Both show a keel 
on the breastbone for the better fixing on of the 
muscles of flight, but the bat’s keel is much less 
prominent than a bird’s. Both show a solidi- 
fying of the middle region of the backbone, 
which affords a firm fulcrum for the wings to 
work against. In almost every other respect 
they are as different as different could be, but 
it may be noted that most birds and most bats 
are small, as if there were a size-limit to flying 
creatures. A bird like an albatross, with a span 
of 11 feet from tip to tip of the outstretched 
wings, is quite out of the common, and so are 
the very large fox-bats of the Far East. 
ATTEMPTS AT FLIGHT 
Apart from man, the problem of flight has 
been successfully solved four times—by in- 
sects, Pterodactyls, birds, and bats; but how 
often has its solution been attempted? It is 
very interesting to study these attempts, some 
of them splendid failures. 
