’Tis a Conglomerated Gland, composed of many smaller ones contained in a common Membrane; each of These sends off an Excretory Vessel, all which do afterwards Unite and Form one Duct (b), which running towards the Roots of the Fangs, discharges the Yellow Liquor into a Bag.
This Bag is fixt to the Basis of the first Bone of the Upper Jaw, and also to the Extremity of the Second, covering the Fangs near the Root (d, [Fig. 10.]). To the upper Part of this Vesicula there is joined another (a), in the Anterior Part of which there is a Passage for the Poisonous Teeth.
This consists of Muscular Fibres, both Longitudinal and Circular, by Means of which it can Contract it self when the Fangs are erected; and by this Contraction the Venom is press’d into the Hole at the Root of the Tooth, and forced out at the Fissure near the Point.
That this is so done, I have frequently observed with the naked Eye, having cut off the Head of a Viper, and immediately pinching the Neck to make it open the Mouth wide; for by this means the Venom was Squirted out as from a Syringe.
When the Viper lyes quiet with its Mouth shut, the Fangs are depress’d and covered with the External Bag; when it intends to bite, it opens the Mouth very wide, at the same time the lower Extremity of the Second of the Common Bones ([Fig. 4. b]) is moved forwards by proper Muscles, and turns as it were upon the fixt Centre (b), thus pushing forward the Upper and Lower Jaws, whose Extremes are united at (c). By this means the Lower Part of the First Bone of the Upper Jaw ([Fig. 3. a]) is thrust forwards, the other Extremity turning in the Cavity of its Articulation, where it is fastned by Ligaments; the Fangs being by this Mechanism Erected, the Bags which covered them, by the Contraction of their Longitudinal Fibres, are pulled back, and the Action of the Circular Ones does at the same Time straiten the Internal Bag, and force the Juice into the Teeth.
Besides this, when the Viper bites, It strikes in the Fangs to the very Root; and thus the Vesiculæ are still more squeezed for the Discharge of the Liquor.
It is worthy our Observation, that the Viper can move the Jaw Bones on one side without moving Those on the other, for they are not joined together at the Extremes as in other Animals; which Contrivance is very beneficial to it in the swallowing its Prey; in that, while the Teeth on one side stand unmoved, and fixt in the Flesh to hold it, Those on the other side are brought forward, to draw it in farther, then they keep it fast till the former Jaws advance again in their Turn. Thus they act successively, and force the Animal intire (there being no Dentes Incisivi or Molares to divide it) into the Œsophagus, whose Muscular Fibres are very Weak, and can help but little in the Business.
It may not be amiss to conclude these Remarks with a short Hint concerning the Organs of Hearing; Mr. Charas (who is however followed by others in it) having, as we mention’d before, Entertain’d a very absurd Opinion about Them.
These then are placed in the Temporal Bones, as in other Animals, and consist of One long, small Bone (Vid. [Fig. 11.]), like that of Birds, whose Extremity is broad, like the Basis of the Stapes in Man, and situated upon a little Hole which opens into the Labyrinth; and besides of three Demicircular Canals ([Fig. 12. a b]) which also open into the Labyrinth.
This Labyrinth ([Fig. 13.]) has a great many Eminencies in it of no determin’d Regular Figure ([Fig. 14.]), and is covered with a Membrane full of Nerves and Blood Vessels. The Nerve enters from the Brain at a Hole in the middle of this Cavity (a, [Fig. 15.]).