Page 79 - Reptiles & Dinosaurs (Britannica Illustrated Science Library)

74 TURTLES AND SNAKES

A Specialized Mouth Primitive Snakes

Boas and pythons are called primitive, since they have neither
fangs nor venom. These snakes have several rows of small,
he most primitive snakes have heavy skulls and few teeth. Most snakes, inward-curving teeth used for holding prey and swallowing quickly
however, have lighter skulls and jointed jawbones. These joints are loose and without letting the prey worm out. This feature is necessary for
T can easily become dislocated so that the snake can swallow prey larger than the snakes to be able to hold onto their prey, since they lack
venom. Venomous snakes, on the other hand, have little
the natural shape of its own head. The teeth are fixed in the upper jaw or the need to worry about their prey escaping, since they
palate, and the fangs for injecting venom may be located either at the front know that, after it is injected with the toxic
substance, it will not be able to get very far.
or at the back of the mouth. Some species, as well as being large and
powerful, have retractable fangs, allowing them to close their mouths
when their fangs are not in use. Injecting Fangs
Cobra species expel their venom in different ways
depending on their fangs. The angle and direction of the
opening determine how forcefully the liquid is injected.

Cranial Anatomy
JACOBSON'S ORGAN
is directly related to each species' diet and—in gives the snake an excellent sense
the case of venomous snakes—to its system for of smell. It consists of two
injecting poison. Most snakes have small skulls with cavities in the palate, into
jawbones that can be separated voluntarily by sliding which the snake brings its
them along a kind of perpendicular rail, which tongue after “tasting” the
consists of a bone called the quadrate. This greatly outside air. That is why
increases the size of the snake's mouth. snakes continually BLACK AND WHITE COBRA BLACK-NECKED COBRA
stick out their Naja melanoleuca Naja nigricolis
It has a jaw with a spur, but
tongues. It must bite its prey in order to
inject venom. it does not actually spit.
DUVERNOY'S
GLAND RETRACTOR FANGS
MUSCLE
GLOTTIS
UPPER JAW

1 Viperid ASIAN COBRA RINKHALS SPITTING
Naja naja
COBRA
This type of skull has small It is the typical cobra, which Hemachatus haemachatus
teeth and large, retractable 2 Colubrid 3 Elapid bites to inject its venom. It can spit great distances.
fangs that are thick or This type of skull lacks front fangs. In this type of skull, the fangs are
hooked. Some species are nonvenomous, located in front, but they are smaller
but others have fangs with a and have only a groove, rather than
QUADRATE groove for delivering venom. a canal, for injecting venom.
Venom System Spitting Venom
consists of the two Duvernoy's glands, one on Forty cobra species can spray their venom
each side of the skull, which produce venom and 6.6 feet (2 m) from a distance. They spray in self-defense
are connected to the fangs. When biting, muscle THE DISTANCE FROM WHICH THE SPITTING when they feel threatened. They can direct
contractions exert pressure on the gland and the stream into an enemy's eyes, causing
TEETH activate the injection mechanism. COBRA CAN KILL BY SPRAYING ITS VENOM grave damage or even death. The shape of
FUSED BONES their fangs is essential to this defense.

The Deadliest Weapon NON-SPITTING
Rattlesnakes have long, thick fangs that are very sharp and The long canal points
kept folded inside their mouths. A movable joint at the base of downward and has a beveled
the fang enables it to stand upright when the snake's mouth edge at the end. The stream
opens to bite. loses momentum.
LENGTHWISE CROSS SECTION
The venom The tooth has a SPITTING
flows through Entrance cavity that SOLENOGLYPHS PROTEROGLYPHS OPISTHOGLYPHS The canal's opening points
the tube and serves as the A The hollow fangs are the B Small fangs in the front of C Fangs in the back, with no forward and is narrow so
directly into canal for the only teeth in the jaw. They the jaw, fixed in position canal or groove. The prey that it can eject the venom
the prey. poison. are long and retractable and with a rear groove for must be held in place. more forcefully.
and inject venom into the conducting venom
Exit Poison Canal prey's tissues.