XVI INTRODUCTION. 
the surface of the skin is divided into small rectangular spaces by trans- 
verse folds traversed by longitudinal grooves or furrows. Limbs are absent, 
or only present in front. Chirotes, a Mexican genus, has the fore limbs; 
the other genera are footless. Most of the species are said to be found in 
or about the nests of ants. One species, Lepidosternon floridanum Bd., 
inhabits the Southeastern United States, 
OpuHip1A.—Serpents. 
The elongate spindle-shaped or subcylindrical form of the snake is a 
familiar one. There are species which present no distinction between head, 
neck, and tail, and there are others in which these parts are well marked. 
The majority have no limbs; a few have rudimentary hind limbs, which 
appear as claws on each side of the vent. A sternum is lacking, but in the 
worm-snakes there are rudiments of a pelvic arch. Most of the serpents 
have teeth on jaws and palate. In consequence of the elastic articulations 
of the bones of the skull and the symphysis of the lower jaws, they are 
able to swallow animals considerably larger than would otherwise be possi- 
ble. All the species of the order are carnivorous. Some crush their prey 
in the folds of the body, others kill the creatures on which they feed by 
venomous secretions, but the greater number swallow living food. During 
the operation of swallowing, small pores along the jaws give out a saliva 
which renders the act more easy. Frequently the snake disgorges a partly- 
swallowed meal to change its position in the mouth, or to take breath; the 
slimy appearance of such morsels has given rise to the erroneous idea that 
they have been deliberately covered with slime before the attempt to dine. 
Movable eyelids do not exist in the Ophidia. The epiderm is continuous 
over body and head, and forms a transparent cover for the eyeball. With 
the slough or cast skin the outer envelope of the eye is carried away; this 
happens at least once in a season. 
Near the time of sloughing or moulting, the dermal covering of the eye is 
loosened, more opaque, and interferes, to some extent, with the sight; at such 
times snakes are said to be blind. Size of ball, shape of pupil, keenness 
of sight, ete., vary according to the habits of the species. Hearing is dull. 
There are no external evidences of ears, and it is most likely the jar felt over 
the whole body from an approaching tread often gives the needful warning. 
The hissing sound produced by expelling the breath from the lungs has been 
supposed to be the nearest approach to a voice, Lately, however, some 
