ORDER III. 
OPHIDII. 
Ciiar. 1 . The head varies in form ; the branches (rami) of the lower jaw-hone are not firmly 
united to each other at their anterior extremities, hut are joined by an extensible ligament which 
allows of their being drawn apart laterally ; the hones of the upper jaw are also connected in 
the same way to the intermaxillary, and allow the same sort of motion. Even the palatine 
hones participate in the general mobility and dilatability, which is still further increased by the 
tympanal bone or pedicle of the lower jaw, which is always suspended to another bone analagous 
to the mastoid process of the temporal, and is attached to the cranium by muscles and ligaments. 
From this structure, and from the mobility and distensibility of each of these bones, it results 
that the mouth may be so widely opened as to receive an object of greater dimensions than the 
animal itself. 
Char. 2. The mouth is of variable size and furnished with lips ; and the upper and lower 
jaws, as well as the palatine arches in all, with only one exception, ( Oligodon ,) are armed with 
teeth. These teeth are solid, of simple construction, and are always situated on the margins of 
the maxillary bones, and not on the inner margin as in some of the lizards. As the serpents 
do not masticate their food, their teeth are organized for seizing and killing their prey or for 
retaining it; they are accordingly pointed and smooth, and curved or arched backward to pre¬ 
vent its escape. 
Char. 3. The tongue is very long, slender, extensible, retractile, within a sheath placed at 
the root, with the apex bifid and terminating in two slender semi-cartilaginous filaments. 
Char. 4. There are no moveable eyelids, nor is there a tympanal membrane. 
Char. 5. The body is exceedingly elongated—destitute of a sternum or of any external organs 
of locomotion—though in some genera {Boa) there are concealed rudiments of posterior limbs near 
the vent. The ribs and vertebrae make up nearly the whole skeleton ; the former surround a 
great portion of the circumference of the body, and are only wanting at the tail ;• the latter are 
curiously arranged ; the body of one is articulated by a convex surface to a cavity in front of 
the succeeding vertebra. The structure of ball and socket allows of free lateral motion, but 
the spinous processes of the back prevent motion up and down to any great extent. The whole 
body is covered above with scales, mostly small and imbricated, and below with large quad¬ 
rangular plates. 
Char. 6. The trachea is very long, and surrounded by simple, complete cartilaginous rings 
only at its anterior half; the lung is single and extends nearly the whole length of the body. 
In some is found a rudiment of a second lung. 
Char. 7. The heart is placed far back, and is provided with two auricles and a single ventricle. 
Char. 8. Serpents are, for the most part, oviparous ; the eggs are covered with a calcareous 
