CROCODILES. 
16 
halves of the lower jaw are united in front by a very short bony union. The 
stout teeth vary considerably in size in different parts of the jaws; the third and 
ninth in the upper jaw, the fourth, and frequently also the first and eleventh, in 
the lower, being generally much larger than the others. In these features caimans 
and alligators resemble many of the true crocodiles; from which they are distin¬ 
guished by the circumstance that, as a rule, both the first and the fourth tooth on 
each side of the lower jaw are received into pits in the upper jaw, so as to be 
invisible externally when the mouth is closed; while the upper teeth bite on the 
outer side of the lower ones. Moreover, the number of teeth varies from seventeen 
SPECTACLED CAIMAN (y s liat. size). 
to twenty on each side of the upper jaw, and from seventeen to twenty-two in 
the lower jaw. Then, again, both these groups are characterised by the very small 
size of the upper temporal fossae on the top of the skull, or those marked T in the 
figure on p. 13; these fossae being in some cases completely obliterated. Caimans 
are specially distinguished by the aperture of the nostrils not being divided in two 
by the nasal bones, by the presence of a strongly developed bony armour on the 
inferior surface of the body, and by the bony plates on the upper surface being 
articulated together. 
Caimans, or jacares, as they are called by the natives of Brazil, are restricted 
to Central and South America, where they are represented by five species. Of 
these, the largest, and at the same time the best known, is the black or great 
