The following briefly discuss about the three major poisonous components in a snake. The components are: 1. Poison Gland 2. Poison Ducts 3. Fangs.
1. Poison Gland
The poison glands, also known as venom glands, are located on either side of the upper jaw, primarily between the eye and the angle of the mouth. Poison glands could be modified superior labial or parotid glands (Figure 1). The poison glands of snakes can be almond-shaped, pear-shaped, or triangular, depending on the species.
Figure 1: Diagram showing the position of poison and Duvernoy’s glands. A. Position of a gland of a proteroglyph snake (Cobra, sea snakes) B. Position of Duvernoy’s and superior labial glands in opisthoglyph snake (Omamental snake). In the picture large grooved fangs are seen at the back of maxilla.
In Naja naja, the shape resembles an almond kernel, whereas in vipers, it is large and tubular. The poison glands’ surfaces can be smooth or lobulate. In Naja naja, the surface is encapsulated with fibrous tissue, and the capsule supports vascular fibrous septa that divide the gland into secretory pockets known as the Poison lakes of Bobeau.
Elapid poison glands (such as cobras and kraits) are made up of long tubules lined with secretory cells. Sea snakes have the elapid type of poison gland. The poison glands of vipers are clumps of tubules. The poison gland section reveals the true structure of an exocrine gland. The gland’s cells secrete poison, which is then stored within the gland.
Temperature affects the secretion of toxins. In some colubrids, the posterior portion of the superior labial gland becomes encapsulated and secretes poison; these glands are known as Duvernoy’s glands. The maximum amount of venom is secreted during the warmest months of the year, while little or none is produced during hibernation.
2. Poison Ducts
The gland is provided with a narrow duct at its anterior end. The duct passes forward along the side of the upper jaw and loops over itself just in front of the fang and opens either at the base of the fang or at the base of the tunnel on the fang.
The duct actually opens in a pocket of mucous sheath that covers the basal part of the fang. In spitting cobras (Naja nigricollis), the poison duct is modified in that it has an “L” shaped bend, just prior to exiting the fang, with the discharge orifice being located on the front of the fang.
Figure 2: Position of a poison gland with accessory poison gland and their primary and secondary duct in a Viperidae snake. The compressor glandulae muscle helps to expel the poison by the pressure.
3. Snake Fangs
A few maxillary teeth in poisonous snakes have been modified to function as poisonous teeth or fangs. Fangs are teeth that have been modified to carry venom. The fangs are enlarged maxillary teeth that regenerate when lost. They are conical in shape, curved, and sharply pointed. At the base of the fangs are an intake aperture and a discharge aperture that is sub-terminal.
Bogert (1943) discovered that the discharge orifice is much smaller in spitting cobras (Naja nigricollis) and South African ringhals (Hemachatus haemachatus), presumably to increase the force of venom. There are two fangs on each side of the maxillary bone in the mouth. The maxilla of the Viperidae has a single large poison fang with small reserve fangs at its base. Fangs are classified into the following types based on the structure and position of the venom canals.
Figure 3: Diagram showing T.S through the tooth of aglyph and fangs of opisthoglyph, proteroglyph and solenoglyph.
Fangs are small, relatively immobile, and located in front of the maxillary bone, a condition known as proteroglyphous. In some species, an open, deep groove runs across the surface of the fangs, but in cobras, the groove’s lips join to form a canal for venom transmission.
A visible suture, which is the line where the lips of the groove meet, goes all the way down to the hole where the waste comes out. Behind the fangs, you can see a few small, strong teeth. There are no grooves or canals in these teeth. This group includes the fangs of cobras, kraits, mambas, and sea snakes (Family Elapidae and Family Hydrophidae, respectively).
At the end of the maxillary bone on the back, there are open-grooved fangs. There are either one or two fangs, and in front of them are a few smaller teeth. This group includes the fangs of snakes like the vine snake (Ahaetulla nasutus), the common cat snake (Boiga trigonata), the Indian flying snake (Chrysopelea ornata), the South African boom slang (Dispholidus typus), and the egg-eating snake (Dasypeltis). Most of the time, a bite from an opisthoglyph snake won’t kill a person, except for South African boom slang. In general, their bites can kill lizards, but they can also kill birds, mice, and rats.
Long, hollow, and located at the back end of the maxillary bone are the canines. The fangs are folded against the roof of the mouth when the jaws are closed and are capable of vertical movement. In this species, venom canals pierce the fangs, transforming them into hypodermic syringes. This category includes the fangs of pit vipers and true vipers (Family Viperidae).
True vipers have long, movable fangs that can penetrate deeply into the tissue of their victims. The fangs of the Gaboon viper are longer than those of other venomous snakes. The fangs of a 1.3-meter-long snake measured 29 millimetres (2.9 centimetres), while those of a 1.83-meter-long specimen measured 45 to 50 millimetres (4.5 to 5 centimetres), which was approximately three times as long as the fang of a 5.5-meter-long king cobra.
All the teeth are solid. Though some may be enlarged and shows fang-like, but these do not possess groove or canal. They are found in all non-poisonous snakes.