116 DIVISION I. VERTEBRAL ANIMALS.—CLASS III. REPTILIA. 
much more than others. Thus, in the tortoises and lizards, respiration is 
the most full and perfect. In the frogs it is much Jess. Following this 
fact, and comparing the extent of respiration with their organs of move- 
ment, M. Brougniart has divided them into four orders, as follows: The 
Chelonians, or Turtles and Tortoises; the Saurtans, or Lizards; the 
Ophidians, or Serpents; and the Latrachians, or Frogs. 
ORDER I. CIHELONIA (The Turtles and Tortoises). 
The Chelonians have a heart with two auricles, and a ventricle with two 
unequal chambers, which communicate together. The blood from the body 
enters the right auricle, and that from the lung the left, but the two streams 
mingle more or less in passing through the ventricle. These reptiles are distin- 
euished by having the body enclosed between two shields or shells, so that 
the head, neck, legs, and tail only appear externally ; and these are capable 
of being retracted in a greater or less degree. The upper shell is formed 
hy the ribs, which are enlarged, flattened, and closely united by sutures ; 
the under shell is the sternum or breast bone, and the vertebr of the neck 
and tail only are movable. In consequence of this conformation, the mus- 
cular system is inverted, in many respects, as with insects and crustacea ; 
and to this circumstance these animals owe their great strength. Tortoises 
rin of the mandibles is covered with horn, as in 
have no teeth; and the mare 
the beaks of birds. They are very tenacious of life, and will move weeks 
after being deprived of the head; and this last will continue to bite long 
after it is severed from the body. They ean remain months, and even years, 
without food. The eggs have a hard shell, and are deposited in the sand. 
The Land Tortoises are distinguished by the convexity of their upper shell, 
and their short toes, enveloped in the common integument nearly to the 
nails. They perish if thrown into the water. 
Genus Trestupo.—The Land Tortoises. These animals are distin- 
guished by a bulged carapace, which is supported by a solid, bony skeleton ; 
their feet are truncated, with very short toes connected nearly to the nails, 
and, together with the head, can be wholly withdrawn within the shell. The 
fore feet have five nails, and the hinder four. They feed chiefly on vege- 
table substances. 
LT. Indica. —This species is distinguished by its large size, measuring 
over three feet in length, and is of a brown color. The Indian species are 
numerous, and most of them are remarkable for their great strength. Mr. 
Bell describes one, which he names Pyxis arachnoddes, that can easily carry 
two men on its back. The hind legs of this Tortoise bear an extraordinary 
