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CHAPTER IV. 
CHELONIANS, OR SHIELDED REPTILES. 
[“ Tue body,” as described by Dr. Gray, “is covered with square 
embedded plates, generally forming a dorsal and ventral shield 
united by their margins, leaving only the head, neck, limbs, and 
tail free, and (in some species, as the Box Tortoises, Czvasternon, 
shut up by movable closely-fitting doors) only covered with a scaly 
skin; the upper shield formed of the ribs united together and 
adherent to the dorsal vertebree by a toothed suture, and surrounded 
by a series of bones forming the edge of the shields; the lower 
shield or sternum, formed of four pairs and acentral anterior, 
bone; the jaws toothless, covered with a horny D'll, rarely hid by 
fleshy lips; eyelids distinct; drum of the ear visible; legs short 
and thick; tail conical.” “The natural dwelling chamber of the 
Cheionia consists chiefly,” says Professor Owen, “and in the 
marine species (Chelone) and Mud Turtles (Z7zonyx) solely, of the 
floor and the roof; side walls of variable extent are added to the 
fresh-water species (Zmjdians) and Land Tortoises ( Zestudintans). 
The whole consists of ‘ osseous plates,’ with superincumbent horny 
plates, or ‘scutes,’ except in the Soft or Mud Turtles (Zrionyx 
and Sphargis), in both of which these are wanting.* 
These animals, to which a portable stronghold is thus given 
in compensation for inferior powers of locomotion and defence, 
are recognisable at a glance from the singular armour with which 
Nature has provided them. A double shield envelopes all parts 
of their bodies, only permitting the head, neck, legs, and tail to 
pass through it; moreover, all these organs can be hidden within 
this double cuirass by means of a retractile power possessed by the 
animal. This double armour consists of a carpace, or back-piece, 
and f/astron, or breast-plate, composed of a series of small bones or 
plates closely united together; the first resulting from the union 
of the sides and dorsal vertebra the plastron or lower buckler, 
* “Circle of the Sciences.” 
