636 REPTILIA. 
The Crocodilians ave oviparous. The eggs have firm cal- 
careous shells, and are laid in holes in the ground. 
Skeletal system.—Numerous transverse rows of sculptured bony 
plates or scutes, ossified in the dermis, form a dorsal shield. On the 
ventral surface the scutes are absent, except in some alligators, in 
which they are partially ossified. But besides and above the scutes, 
there are horny epidermic scales like those in other Reptiles. The hide 
is often used as leather. 
‘ The vertebral column 
= consists of distinct cer- 
/ vical, dorsal, lumbar, 
sacral, and caudal verte- 
bree, all proccelous except 
the first two cervicals, 
the two sacrals, and the 
first caudal. In most 
of the pre-cretaceous 
Crocodilians, however, 
the vertebree were amphi- 
coelous. The centra of 
the vertebree are united 
by fibro-cartilages, and 
the sutures between the 
neural arch and the cen- 
trum persist at least for 
a long time. Chevron 
bones are formed beneath 
the centra of many of 
the caudal vertebrz. 
Many of the ribs have 
two heads — capitulum 
and tubercle—by which 
they articulate with the 
vertebree. From seven 
to nine of the anterior 
Fic. 349.—Cervical vertebra of crocodile. dorsal ribs are connected 
7.S., Neural spine; P.A., posterior articular pro- with the sternum by 
cess; A.A., anterior articular process; C.R., sternal ribs, and from 
cervical rib; C., proccelous centrum, several of these anterior 
ribs cartilaginous or par- 
tially ossified uncinate processes project backwards. The so-called 
abdominal ribs have nothing to do with ribs, but are ossifications in 
the fibrous tissue which lies under the skin and above the muscles. 
They form seven transverse series, each composed of several ossicles. 
As to the skull, there is an interorbital septum with large alisphenoids ; 
the presphenoid and orbitosphenoids are at best incompletely ossified ; 
all the bones are firmly united by persistent sutures; both upper 
and lower temporal arcades are completely ossified ; the maxille, the 
palatines, and the pterygoids meet in the middle line of the roof of 
