4 
REPTILES. 
by a leathery membrane like that of bats. In a typical Reptile, such as a lizard 
or crocodile, both pairs of limbs are well developed, and of approximately equal 
length • but in the snakes all external traces of limbs have disappeared; while 
in the extinct flying dragons, or Pterodactyles, the fore-limbs much exceed the 
hind ones in size, and in many of the so-called Dinosaurs, which are likewise 
extinct, the excess in size falls to the share of the hinder pair of limbs. In 
other cases, again, the limbs may be modified into paddles, adapted for progres- 
SKELETON OF FISH-LIZARD, OR ICHTHYOSAUR. 
sion in the water, as in the existing turtles, and the extinct fish - lizards or 
Ichthyosaurs; the body in the latter assuming a somewhat fish-like form. In 
nearly all cases Reptiles have long and well-developed tails; although in some of 
the flying dragons these be¬ 
come rudimentary. 
A large number of Rep¬ 
tiles are characterised by the 
development of bony plates 
within the deep layer of the 
skin; such plates, which are 
well displayed in existing 
crocodiles, being overlain by 
horny shields, and thus 
corresponding in every re¬ 
spect with those forming 
the carapaces of the arm- 
aclilloes among Mammals. 
Among certain extinct 
Dinosaurs these bony plates 
attain a development un¬ 
paralleled at the present 
day; and in some they are 
believed to have occupied the extraordinary position shown in the accompanying- 
figure. 
RESTORED SKELETON OF ARMOURED DINOSAUR (about ^ nat. size). 
sc, shoulder-blade, or scapula ; co, coracoid ; h, upper arm-bone, or 
humerus ; r, u, bones of fore-arm, or radius and ulna ; c, wrist or carpus ; 
me, metacarpus ; il, liaunch-bone, or ilium ; p, pubis ; is, ischium ; f, 
thigh-bone, or femur ; ti, ji, bones of lower leg, or tibia and fibula ; ta, 
ankle, or tarsus ; mt, metatarsus.—After Marsh. 
Still , more remarkable differences exist with regard to the form and structure 
of the teeth; which, instead of being, as in the two preceding classes, strictly 
confined to the borders of the jaws, may be spread over the entire palate. 
In spite, however, of this diversity of form, the teeth of Reptiles differ from many 
of those of the majority of Mammals in that they are never implanted in the 
