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The following points highlight the three major poisonous components in a snake. The components are: 1. Poison Gland 2. Poison Ducts 3. Fangs.
Snake: Poisonous Components # 1. Poison Gland:
The poison glands or venom glands (Fig. 8.29), are situated one on either side of the upper jaw, mainly in the space between the eye and the angle of the mouth. The poison glands are possibly the modified superior labial or parotid glands. Depending upon the species of snakes the poison glands may be almond shaped, pear shaped or triangular.
In Naja naja, the shape becomes of an almond kernel and in vipers, it is large and tubular shaped. The surface of the poison glands may be smooth or lobulate. The surface is encapsulated with fibrous tissue in Naja naja and capsule supports vascular fibrous septa, separating the gland into secretory pockets, called the Poison lakes of Bobeau.
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The poison glands of elapids (e.g., cobras and kraits) consist of long tubules lined with secretory cells. The elapid type of poison gland is found in sea snakes. In vipers, the poison glands consist of clumps of tubules. The section of poison gland reveals the true structure of an exocrine gland. The cells of the gland secrete poison which ‘stores within gland.
Temperature is related to the secretion of poison. In some colubrids the posterior part of superior labial gland becomes invested with a layer of capsule, secrets poison, called Duvernoy’s glands (Fig. 8.29B). The secretion of venom is maximum during the warmest months of the year and little or no venom during hibernation.
Snake: Poisonous Components # 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 (Fig. 8.30).
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.
Snake: Poisonous Components # 3. Fangs:
In poisonous snakes a few maxillary teeth are modified to act as poisonous teeth or fangs. The teeth when modified for conducting venom, called fangs. The fangs are conical, curved shaped, sharply pointed and are enlarged maxillary teeth which regenerate when lost. An intake aperture is at the basal part of the fangs and a discharge aperture which is sub-terminal.
In spitting cobras (Naja nigricollis) and South African ringhals (Hemachatus haemachatus), Bogert (1943) has shown that the discharge orifice is much smaller presumably to increase the force of venom.
The fangs are one on each side of the maxillary bone of the mouth. In the Viperidae, there is a single, large, poison fang on the maxilla with small reserve fangs at its base. Fangs are of the following types, depending on the structure and position of the venom canals (Fig. 8.31).
(a) Proteroglypha (Ck. Proto = first, glyph = hollowed):
Fangs are small, relatively non-movable and situated at the front of the maxillary bone, a condition called proteroglyphous. In some species an open deep groove runs on the surface of the fangs but in cobras the lips of the groove join to form a canal for conducting venom.
A visible suture, representing the line where the lips of the groove join together, runs down to the discharge orifice. Several small solid teeth are seen behind the fangs. These teeth are without grooves or canals. Fangs of cobras, kraits and mambas (Fam. Elapidae) and sea snakes (Fam. Hydrophidae) are included in this category.
(b) Opisthoglypha (Ck. Opistho = behind):
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Fangs with open groove are situated at the posterior extremity of the maxillary bone. The fangs are either one or two in number with few smaller teeth in front.
The fangs of vine snake (Ahaetulla nasutus), common cat snake (Boiga trigonata), Indian flying snake (Chrysopelea ornata), South African boom slang (Dispholidus typus), egg eating snakes (Dasypeltis) are in this category. The bite of opisthoglyph snakes is not usually lethal to human beings except South African boom slang. Generally their bite may be lethal to lizards, but sometimes birds, mice and rats.
(c) Solenoglypha (Gk. Solen = Pipe):
Fangs are long, hollowed and situated at the rear end of the maxillary bone. They are capable of vertical movement and are movable in which the fangs are folded against the roof of the mouth when the jaws are closed. In this type, fangs are pierced by venom canals, thus acting as hypodermic syringe. The fangs of pit vipers and true vipers (Fam. Viperidae) fall in this category.
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The long movable fangs of true vipers can penetrate deep into the tissues of the victims. The Gaboon viper possesses longest fangs as compared with fangs of other venomous snakes. A 1.3 metres (51″) long snake had fangs of 29 millimeters (2.9 cm) and 45 to 50 millimeters (4.5-5 cm) fangs in a 1.83 metres (6 ft.) long specimen which was about 3 times long as compared with a fang of a 5.5 metres long king cobra.
(d) Aglypha:
All the teeth are solid. Though some may be enlarged and shows fang-like, but these do not possess groove or canal (Fig. 8.31). They are found in all non-poisonous snakes.
