This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
(1916). The Chameleon is another curious example of a reptile obliged to employ its tongue in securing insect prey. The Chameleon is arboreal in its habits: its feet, cleft as it were into two portions, firmly grasp the boughs upon which it climbs; while its well-known power of changing the colour of its skin, so as to imitate that of the branches around it, efficiently conceals it from observation. The tongue of this creature, when extended, is as long as its whole body, and is terminated by a club-shaped extremity smeared over with a viscid secretion: when an insect comes within a distance of five or six inches from the Chameleon, the end of this tongue is first slowly protruded to the distance of about an inch, and then, with the rapidity of lightning, launched out with unerring aim; the fly, glued to its extremity, is with equal velocity conveyed into the mouth.
(1917). The jaws of the Chelonian Beptiles are not armed with teeth, but cased in horny coverings, so as to resemble the beak of a bird, with which they crop the vegetable aliment upon which they generally subsist.
(1918). Serpents, as regards their means of destroying prey, may be divided into two great groups - the first including those which are not venomous, the second embracing such as are armed with poison -teeth.
(1919). In the non-venomous Serpents, as for example in the Boa Constrictor, the upper jaws and the palate-bones are all lined with sharp teeth, so that there are four rows of dental organs, two placed along the margins of the maxilla, and two projecting from the roof of the mouth: all these teeth are simple, very sharp, and point backwards. Each division of the lower jaw is likewise armed with a single row, which are also directed towards the back of the mouth. It must be evident, from a mere inspection of these teeth, that they can be of little use in holding, much less in destroying, such strong and large animals as the Boa devours; and upon a little consideration we shall find that they are intended for a very different office. These serpents kill their victims by coiling their lengthy bodies around the chest, and then by strong muscular contraction they compress the thorax of their prey so firmly, that, its movements being completely prevented, respiration is put a stop to, and the animal so seized speedily perishes from suffocation.
But, having succeeded in extinguishing life, the most difficult task still remains to be accomplished: how is the serpent, utterly destitute as it is of all external limbs, to force down its throat the carcase of a creature many times thicker than its own body? The mode adopted is as follows: - once more winding itself around the slain animal, it commences at the head, which by main force it thrusts into its mouth; the elastic ligament at the symphysis of its lower jaw gives way, and the branches of the inferior maxilla become widely separated, so that the mouth is stretched enormously as the food is thus forced into it. Deglutition is here a very lengthy and laborious process; and were there not some special contrivance to guard against such an accident, no sooner were the efforts of the snake relaxed in the slightest degree than the muscles of the throat and jaws, being in a state of extreme tension, would force out of the mouth what had already been partially swallowed. To provide against this, the teeth are in this case converted into a sort of valve: pointing backwards, as they all do, they permit the bulky food to pass into the fauces; but at the same time their sharp points, being directed towards the throat, efficiently prevent it from being pushed back again in the opposite direction*.
(1920). In the venomous serpents, those teeth which are fixed to the margin of the superior maxillary bone of the innoxious genera are generally deficient; and instead of them there is found an apparatus of poison-fangs, constituting perhaps the most terrible weapons of attack met with in the animal creation. The poison-teeth (fig. 337, a) are two in number, one fixed to each superior maxillary bone: when not in use, they are laid fiat upon the roof of the mouth, and covered by a kind of sheath formed by the mucous membrane of the palate; but when the animal is irritated, or about to strike its prey, they are plucked up from their concealment by muscles inserted into the upper maxillary bone, and stand out like two long lancets attached to the upper jaw. Each fang is traversed by a canal - not, as it is generally described, excavated in the substance of the tooth, but formed by bending, as it were, the tooth upon itself, so as to enclose a narrow channel through which the poison flows. The canal so formed opens towards the base of the tooth by a large triangular orifice; but at the opposite extremity it terminates near the point of the fang by a narrow longitudinal fissure. The gland wherein the poison is elaborated occupies the greater part of the temporal fossa, and is enclosed in a white and tendinous capsule (fig. 337, h); the substance of the organ is spongy, and composed of cells communicating with its excretory duct (c), by which the venom is conveyed to the opening at the base of the fang 1. The poison-gland is covered by a strong process of the temporal muscle (d), which is attached to a thin aponeurotic line (e.) The greater portion of the fibres of this muscle take their origin from the capsule of the secreting apparatus, which they partially envelope; and then winding round all the posterior part of the gland, and passing behind the commissure of the lips, the lower part of the muscle is firmly implanted into the lower jaw very far anterior to the angle of the mouth. The process of the temporal muscle which thus surrounds the gland is very thick and strong, so that it is easy to imagine with what force the poison will by this mechanism be injected into the wounds inflicted by the fangs, seeing that the same muscles which close the jaw at the same time compress the bag of venom with proportionate energy.