l88 THE LIVING ANIMALS OF THE WORLD 
disfavour with which these reptiles are commonly regarded. Among the uneducated even at 
the present day it is not unusual to hear the tongue, with reference to its peculiar shape 
and vibrating action, pronounced to be the seat and instrument of the animal’s poisonous 
properties. The swift, silent, stealthy, gliding motions with which, apart from any visible 
organs of locomotion, a snake slides, as it were, along the ground and over all obstacles fill 
to the brink the measure for its condemnation in the estimation of all but the snake-devotee 
or the naturalist. 
The locomotion of the snake is, as a matter of fact, one of the most remarkable 
and beautifully contrived phenomena in animal mechanics. The peculiarly jointed and 
abnormally mobile ribs constitute the mystic de7is ex mac/iind by which the reptile accom- 
plishes its migration. These ribs articulate in pairs by a single mobile head with their 
respective segment of the vertebral column. At ^their opposite extremity they impinge 
on and are in muscular connection with the broad, slightly overlapping, shield-like scales 
which clothe the under surface of the body. The rib-muscles, contracting in rhythmical 
succession, raise the free overlapping edges of the shield-like scales, which, striking against the 
ground in the same regular order, push the body forward. Adopting an easily comprehensible 
simile, the snake’s body is 
carried along the ground on 
the same principle as a pad- 
dle-wheel steamer is pushed 
along the surface of the water, 
the paddle-boards in the case 
of the snake being affixed to 
a long, narrow plane instead 
of a circular w'heel. 
The poison-fangs of 
snakes are highly specialised 
structures, and their presence 
or otherwise was formerly 
considered sufficiently dis- 
tinctive for the separation 
of these reptiles into two 
sharply dcfinednatural series. 
More recent investigations 
have, however, shown that 
such a system of classification is entirely artificial, both venomous and harmless species 
occurring among groups which are related to one another by essential structural characters. 
The teeth in the ordinary or harmless snakes are usually represented by two rows of slender, 
recurved, sharply pointed teeth in the upper jaw, and a single row of a similar character in 
the lower one. This recurved character of the dentition effectively assists the snake in gorging 
its quarry whole, nothing once seized by the hook-like teeth having a chance of retreating, 
the snake itself being unable to eject the prey upon which the teeth have fastened. In the 
most poisonous series, such as a rattle-snake, there is but a single row of recurved teeth in 
the upper jaw, and these are the equivalents of the inner set of the harmless species. Among 
the most venomous snakes the poison-fangs are tubular in character, the poison being received 
from the venom-glands at their open base, and discharged at the apex. In other forms the fangs 
have grooved channels only for the passage of the virus, while in the other species there may be 
an intermediate condition. In all cases the poison-secreting glands are modifications of the 
ordinary salivary glands of other vertebrate animals. They are situated, one on each side, 
immediately below and behind the eyes, and are in some instances so abnormally dev^eloped 
as to extend backwards along the sides of the body. Special muscles envelop these glands, 
and force the poison into the hollow base of the fangs when the mouth is opened to strike. 
Hoto by H. G. F. Spurn. I, h ?.] lEailbourne 
DARK GREEN SNAKE 
Closely allied to the rat-snake of India, and preys in a similar manner on rats, mice, and birds 
