RULERS OF THE ANCIENT SEAS 53 
of Africa and Asia, especially adapted to a 
roving, predatory life by their powerful tails 
and paddle-shaped feet. Their cup-and-ball 
vertebre indicate great flexibility of the body, 
their sharp teeth denote ability to capture slip- 
pery prey, and the structure of the lower jaw 
shows that they probably ate in a hurry and 
swallowed their food entire, or bolted it in 
great chunks. The jaws of all reptiles are 
made up of a number of pieces, but these are 
usually so spliced together that each half of the 
jaw is one inflexible, or nearly inflexible, mass 
of bone. In snakes, which swallow their prey 
entire, the difficulty of swallowing animals 
greater in diameter than themselves is sur- 
mounted by having the two halves of the lower 
jaw loosely joined at the free ends, so that 
these may spread wide apart and thus increase 
the gape of the mouth. This is also helped by 
the manner in which the jaw is joined to the 
head. ‘The pelican solves the problem by the 
length of his mandibles, this allowing so much 
spring that when open they bow apart to 
form a nice little landing net. In the Mosa- 
saurs, as in the cormorants, among birds, there 
