264 VERTEBRATE ANIMALS. 
The Land Tortoises have short legs of nearly equal length, 
the toes little distinct, and united into a sort of stump, with 
indistinct, horny claws. Good examples of this group are the 
common European Tortoise (Zestudo Greca) and the Indian 
Tortoise (7. /zdica), the last attaining a length of over three 
feet. 
ORDER IJ. OPHIDIA.—This order includes most of the ani- 
mals which would commonly be called snakes or serpents, and 
is characterised by the following peculiarities: The body is 
always more or less elongated, worm-like, or cylindrical, and 
the skin develops horny scales, but never bony plates. There 
is never any breastbone (szerzzzz), nor pectoral arch, nor fore- 
limbs ; nor, as a rule, are there any traces of hind-limbs, In 
a few cases, however, rudimentary hind-limbs can be detected. 
The ribs are always very numerous. The two halves of the 
lower jaw are composed of several pieces each, and they are 
united to one another in front only by ligaments and muscles 
(fig. 138). Hooked, conical teeth are always present, but they 
are never lodged in distinct sockets, and are only used to hold 
the prey, and not in mastication. The lungs and other paired 
organs are often not symmetrical, one of each pair being usually 
smaller than the other, or altogether absent. 
The most striking of these characters of the snakes (fig. 142) 
is to be found in the nature of the organs of locomotion. The 
fore-limbs are invariably altogether wanting, and there is no 
pectoral arch nor breastbone ; nor, as a rule, are there any 
traces of hind-limbs. In a few forms, however, the hind-limbs 
are present in an extremely rudimentary form, never exhibiting 
any outward evidence of their existence, beyond the occasional 
presence of short horny claws or spurs. In the entire absence, 
then, or rudimentary condition of the limbs, the snakes progress 
by means of the ribs, which are always excessively numerous, 
and, in the absence of a breastbone, are also extremely movable. 
Their free ends, in fact, are simply attached by muscular fibres 
to the scales or “scutes,” which cover the lower or abdominal 
surface of the animal. The number of ribs varies from 50 up 
to 320 pairs, and by means of this arrangement the snakes are 
able to progress rapidly, walking, as it were, upon the ends of 
the ribs. Their movements are also much assisted by the 
extreme flexibility of the whole spine, caused by the cup-and-ball 
