Venoms: Venomous Animals and Antivenomous Serum-therapeutics. A. Calmette
A, and fig. 3). They are traversed by an almost completely closed canal, from the base, which communicates with the poison-duct, to the neighbourhood of the point, where it opens very obliquely on the convex surface (fig. 3, A and D).
Fig. 4.—B, Fang of one of the Colubridæ (Naja tripudians); E, transverse section.
Fig. 5.—C, Fang of one of the Hydrophiinæ (Hydrophis pelamis); F, transverse section.
Fig. 6.—Three transverse sections of a poison-fang of one of the Colubridæ, through A A, B B, C C; P P, pulp cavity; V V V, poison-canal (groove). (After C. J. Martin.)
In the Elapinæ sub-family of the Colubridæ, and especially in the Hydrophiinæ, the teeth are much shorter and simply grooved or canaliculate; that is to say, the canal communicates with the exterior throughout its extent by a narrow slit, which traverses the entire convex surface of the tooth (figs. 4, 5, and 6).
It does not follow from this that the bites of these reptiles are less dangerous; the contrary, indeed, is the case, for their venom is infinitely more active.
These differences, as well as the particular mode of arrangement of the other little non-poisonous teeth in both jaws, enable us in many cases to recognise, by the mere appearance of the bite, the species of snake by which the bite has been inflicted.
Fig. 7.—Marks produced on the Skin by the Bites of different Species of Snakes.
I. Non-venomous Colubrine.—The bite is marked only by the imprint of from 35–40 small palatine or pterygoid teeth, and 20–22 upper maxillary teeth (on the outside of the foregoing) on each side.
II. Venomous Colubrine (Naja tripudians, Proteroglypha).—The bite exhibits 25 or 26 punctures from the pterygoid or palatine teeth, and, on each side, one or two, rarely three, circular wounds produced by the principal poison-fangs and by the reserve teeth.
III. Viperidæ (Solenoglypha).—The sole indication of the bite consists of 8 or 10 punctures from the palatine or pterygoid teeth, and one little round wound, on each side, produced by the poison-fangs.
(After Sir Joseph Fayrer.)
Fig. 7, above, shows how it is possible to distinguish the marks left by a non-venomous reptile, and by one of the Proteroglypha or Solenoglypha respectively.
Poison-glands.—The poison-glands occupy an extensive inter-muscular space behind the eyes, on each side of the upper jaw. They are oval in shape, and may, in Naja tripudians for example, attain the size of a large almond (fig. 8).
Their structure is the same as that of the salivary glands of the larger animals. The poison that they secrete accumulates in their acini and in the efferent duct that opens at the base of the corresponding fang.
Each gland is surrounded by a capsule, to which are partly attached the fibres of the masseter muscle, which violently compresses it and drives the poison, just as the piston of a syringe would do, into the canaliculi or groove of the fang.
Fig. 8.—Poison-gland and Fangs of a Venomous Snake (Naja tripudians, Colubridæ). (Natural size.)
L, Lobe of the gland; D, poison-duct; F, fang attached to the maxillary bone; G G, gland; M, capsule of mucous membrane surrounding the fangs; R, reserve fangs; A A, muscular fascia covering the gland.
(After Sir Joseph Fayrer.)
In a few venomous snakes the gland is developed to such an extent that it extends as far as the first ribs.
The species, on the contrary, that have the poison-teeth placed in the hinder part of the mouth (Opisthoglypha) have glands but little developed.
Muscular Apparatus of the Head.—Figs. 9 and 10, 11 and 12 show the arrangement of the principal muscles that work the jaws and glandular organs in Vipera russellii and Naja tripudians, which respectively represent the most formidable types of Viperidæ and venomous Colubridæ.
It is not necessary to give a detailed description of each of these muscles. Let it suffice to point out that all contribute in giving the greatest elasticity to the jaws, and at the same time strength sufficient to retain the prey and to cause it to pass from front to rear towards the œsophagus, by a series of alternate antero-posterior movements and analogous lateral ones. By means of these movements, which are participated in by the upper and lower maxillary bones, the palatines, mandibles or inter-maxillaries, and the pterygoids, the animal in a manner draws itself over its prey like a glove, since the arrangement of its dentition does not admit of mastication.
A A, Fascia covering the anterior and posterior temporal muscles; B, small gland; C, tendinous insertion of the fascia; D, poison-duct; E, poison-fang; F, reserve fangs; G, mandible; H, ectopterygoid muscle; J, poison-gland covered by the masseter; K, masseter inserted in the mandible; L, insertion of the temporal muscle; M, digastric muscle.
A A, Ectopterygoid muscle; B, præ-spheno-pterygoid muscle; C, intermandibular muscle; D, præ-spheno-palatine muscle; E præ-spheno-vomerine muscle; F, capsule of mucous membrane surrounding the fangs; G, long muscle of the neck.
Figs. 9 and 10.—Muscular Apparatus and Poison-gland of Vipera russellii (Viperidæ). (After Sir Joseph Fayrer.)
A, Tracheo·mastoid muscle; B B, digastric muscle; C C, posterior temporal muscle; D D, anterior temporal muscle; E E, masseter; F, poison-gland, covered by the masseter and fascia; G, poison-duct; H, maxillary bone; I, neuro-mandibular muscle; J, costo-mandibular muscle.
A, Entopterygoid muscle; B, poison-gland; C, poison-duct; D, poison-fangs; E, præ-spheno-palatine muscle; F, præ-spheno-vomerine muscle; G, capsule of mucous membrane surrounding the fangs; H, præ-spheno-pterygoid muscle (which erects the fangs); J, inter-mandibular muscle; K, ectopterygoid muscle; L, long muscle of the neck (longus colli).
Figs. 11 and 12.—Muscular Apparatus and Poison-gland of Naja tripudians (Colubridæ). (After Sir Joseph Fayrer.)
Fig. 13.—Arrangement of the Scales of the Head in one of the Non-poisonous Colubridæ (Ptyas mucosus). (After Sir Joseph Fayrer.)
A, Rostral scale; B, anterior frontals; B1, posterior frontals; C, vertical; D, occipitals; E, supra-ciliaries; F, temporals; L, M, nasals; N, loreals, or frenals; O, anterior oculars, or præ-orbitals; P, posterior oculars, or post-orbitals; Q, supralabials; G, median infralabial; H H, lateral infralabials; I K, mentals.
The enormous extensile power of the mouth and œsophagus thus enables snakes to swallow animals, the size of which is several times in excess of their own diameter.
Deglutition is slow and painful, but the gastric and intestinal juices are so speedy in action, that the digestion of the most resistant substances rapidly takes