In repeated Dissections of the Viper, comparing the Descriptions given Us by Authors with the Parts themselves, I have found them in many Particulars to be very Defective. I shall however at present confine my self to some Observations made chiefly on those Organs which serve to prepare and emit the Poison.

To begin therefore with the Head. The Skull (Fig. 2.) is composed of several Bones, joined together by Sutures, as in Man, but with this Difference, that the Os Frontis in the Viper consists of Two Bones united by a Rectilinear Suture, and the Parietal Bones are entire; whereas in Man the Parietal Bones have Sutures, and the Os Frontis is entire.

(a) Shews Two small Semicircular Bones, which form the inferior Part of the Nostrils.

(b) The Two Bones which make the upper Part of the Nose, from the latter pass down two thin Laminæ, which touching one another, and falling perpendicular upon the Ossa Palati, compose the Septum of the Nose.

(e e) Point out the Ossa Frontis, which form the upper Part of the Orbits of the Eyes. And (c c) the Orbits themselves.

The Parietal Bones (d) make a large Cavity, in which the greatest Part of the Brain is contained, and this we may call the Sinciput.

Behind this Bone are placed the Ossa Temporum (f f) in which lye the Organs of Hearring; and behind Them a Bone (g) which, we may call the Os Occipitis, covers the posterior Part of the Brain. This is joined to the first Vertebra of the Neck (h), by a Spherical Articulation, as all the Vertebræ are to one another; and this is the Reason why this Creature can turn its Head and Body so much, and so nimbly, every way.

To some of These there are Two other Bones Articulated for particular Uses.

The First of Them, which serves as a Basis to the Articulation of the Rest (a, Fig. 4.), is fastned by one Extremity to a small Proturberance (i, Fig. 2.) in the middle and lateral Part of the Os Sincipitis, and running back towards the Vertebræ, lyes in the same Plain with the Sinciput. This Bone has a Motion, tho’ very inconsiderable, both upwards and downwards. By means of This, the opening of the Mouth is somewhat inlarged in the Time of Deglutition.

That End of this Bone, which is next to the Vertebræ, is articulated at oblique Angles with Another (b) placed Horizontally, and whose Motion is forwards and backwards, being made chiefly for moving the Bones of the upper and lower Jaw, into which the Teeth are inserted. By reason of this kind of Articulation, It cannot contribute any thing towards widening the Mouth for Swallowing.

This Bone, and That with which it is joined, I call the Common Bones.

The Upper Jaw (Fig. 3.) is, besides the Teeth, composed on each side of three Bones. The First (a), into which the Poisonous Fangs are fixt, is articulated with the Anterior Protuberance of the Orbit of the Eye; and has a Motion of Flexion and Extension, that is, forwards and backwards, by which the Fangs are Erected or Depress’d. It is small at the Joint, but grows broader by degrees, to a pretty large Basis, the better to contain a considerable Number of Teeth. It is Spongy like the Substance of the Vertebræ, and no ways fit to be the immediate Organ of Hearing, as Mr. Charas and some others have imagined.

The Second (c), is a broad thin Bone, Articulated by one Extreme to the Former, (f), and by the other firmly fixt to the middle of the third Bone. When this is thrust forwards, it likewise pushes the First, and by this means the Erection of the Fangs is helped; and when it is pull’d backwards, they are depressed.

The third Bone (e d), is join’d by one Extremity (e), to the End of one of the Bones of the Lower Jaw (c, Fig. 4.), And being somewhat crooked, turns in a little towards the Basis of the Cranium, and running along the Inferior Part of it towards the Nose, terminates near the Internal and Anterior Part of the first Bone.

The Lower Jaw (c d e f g, Fig. 4.) on each side is made up of two Bones, but firmly united, the Extremity of the one entring within the other (f). The First (c d e) articulates with the Second of the Common Bones (b), where it is broad, and sends off an Apophysis, into which there is a Muscle inserted, which helps to open the Jaw. There is in this is a Hole (d), for the Entrance of the Branch of the Nerve, which passing thro’ a Canal in the middle of it, goes to the Extremity of the Second Bone, and in its way sends off several Branches which go to the Teeth; and also a very considerable one, which goes out at (e), and is wholly spent upon the Neighbouring Muscles.

The Second Bone (f g) serves chiefly to receive the small Teeth, which answer to those in the upper Jaw.

As for the Teeth, they are of two Sorts, the Great, or poisonous Fangs, and the Small.

The Great (b, Fig. 3.), being fixt in the First Bone of the Upper Jaw, are Crooked and Bent, like the Dentes Canini in most Carnivorous Animals. They are manifestly hollow from their Root a considerable way, not to the very Apex or Point, (which is solid and sharp, the better to pierce the Skin) but to a small distance from it, as is plainly seen by splitting the Tooth thro’ the middle (Vid. Fig. 6.). This Cavity ends at the Convex Part in a visible Slit, very well resembling the Nip or Cut of a Pen (Fig. 9. d), which is the Emissary or Outlet to the Poyson.

Galen (37) has given us a considerable Hint of this Make of the Tooth: For, The Mountebanks (He says) used to suffer themselves to be bit by Vipers, having first with some Pastes stopt the Holes of their Teeth, that the Venom being thus kept in, the Spectators might think they did by their Antidote secure themselves from its dangerous Effects.

The Reason why these Teeth are Crooked, is, That the Point of the Tooth, when the Viper bites, may be Perpendicular to the Part to be Wounded; for the Head being raised back in the Time of Biting, and the Tooth erected, if this were strait, It would not, by reason of its oblique Situation to the part, enter with so much Force, nor so deep into the Flesh.

As for the Number of the Poisonous Fangs, I have observed, that there are, for the most part, besides One, Two or Three on each side, fixt Perpendicularly to the first Bone of the Upper Jaw, some others which are Young, and of a smaller Size, adhering to the same Bone: Their Points are hardened, and they have their Fissures formed as in the other, but their Roots are Soft and Mucilaginous, like the Roots of the Teeth in Infants, and so they lye always depress’d at the Bottoms of the Former, as may be seen Fig. 10. c.

They drop off from the Bone at the least Touch; and therefore some Anatomists have imagined them to be fastened to Muscles or Tendons, which would have rendred Them altogether Useless. For they are made to supply the Place of the Greater, when they fall away, or are pulled out by Accident, and in order to do this, they do by degrees harden, and rise more and more, till at last they stand upright, and come to a Perpendicular Situation in the Bone.

They are not all of the same Growth, for in some we can only discern the Shape of a Tooth without any Hardness, in others the Point, and in the next somewhat more is hardened, and so on to the greatest Fang.

Their Number is very uncertain, there being sometimes six or seven in each side of the Jaw, sometimes fewer.

These seem to have occasioned the Disputes among the Ancients concerning the Number of the Viperine Teeth.

The Poysonous Fangs have small Holes at the Internal Part of their Root, thro’ which the Vessels pass which carry their Nourishment (Fig. 5. a).

It is remarkable, that Nature has provided Young Vipers with Poisonous Teeth grown to their Perfection, that so they may kill their Prey as soon as they come into the World.

The Second Kind of Teeth, or the Small, are hooked, and bent, as well as the former, but without any Slit or Opening. Of These there are Four Rows, Two on each side of the Mouth. They are fixt in the third Bone of the Upper Jaw, and in the Second in the Lower, as exhibited to view in the Figures.

Their Use is to hold the Prey fast while Execution is done by the Bite, lest in struggling to get away, It should pull out the Fangs.

The Instruments that Emit the Venom being thus describ’d, we come next to those which serve to Prepare and Contain it.

This Liquor is separated from the Blood by a Gland on each side of the Head, placed in the Anterior and Lateral Part of the Os Sincipitis, just behind the Orbit of the Eye (Fig. 9. a); It lies immediately under that Muscle which helps to depress the Fangs, so that by the Action of this it is Press’d; which is an admirable Contrivance to forward the Secretion of the Juice out of it.

’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.).

There is no Cochlea in the Ear of the Viper; but the Anterior Demicircular Canal opens into a Semicanal, which makes some Spiral Turns in the Fore-part of the Labyrinth; in like manner as it is in Fish.

The Passage for the Air to these Organs is not Outward, but, as in some Fish, thro’ the Mouth, between the Upper and Under Jaws, running below the Second of the Common Bones. But of This, and also of the True Mechanic Use of the aforesaid Parts, more hereafter.