_DENTITION._
IN the preceding pages it may have been observed that the adage, ‘There
are no rules without exceptions,’ occurs so frequently in ophidian
physiology that the latter are almost in the majority. Concerning the
teeth especially, the forms of dentition in the various families, the
distinction of species by them, the size and position of poison fangs,
etc., the rules involve so many exceptions that we can perhaps render
the subject less perplexing by dispensing with rules altogether. ‘The
gradations of teeth are very imperceptible,’ said Prof. Huxley in
his lecture at the London Institution. So numerous are their stages
of development that there is really no well-defined gap between the
venomous and the non-venomous species. ‘We do not know for certain
whether the ordinary teeth are poisonous or not,’ Huxley also said.
The recent researches into the nature of salivary secretions will
throw more light on this subject. A large non-venomous snake, like
other normally harmless animals, if biting angrily, with its abundant
salivary glands pouring secretions into its mouth, might inflict a
very ugly wound, especially on a feeble or frightened victim.
A few rules may, however, safely be offered as ‘without exception,’ and
these I will point out in order to clear the way a little towards a
better comprehension of the exceptional ones.
All true snakes, poisonous or not, that have teeth at all, have the six
jaws described in the first chapter, viz. the right and left upper jaw,
the right and left lower jaw, and the right and left palate jaw. The
latter are called ‘jaws,’ not anatomically, but merely as answering the
same purpose, being furnished with teeth; each true jaw and the palate
being considered as two or a pair, on account of the independent action
imparted to each by the especial muscles and the elastic tissue which
unites them, where in the higher animals they are consolidated.
With but one exception (the _egg-eating Oligodon_ or _Anodon_ family)
all other true serpents, whether venomous or not, possess the two rows
of palate teeth.
All can move or use each of the six jaws, or any two, three, or more of
them independently, as we observed in feeding, some of the six holding
the prey while others move on. Some writers have conveyed the idea
that there is a regular alternation and even rotation of the jaws in
feeding, No. 1, 2, and so on in succession till all the six have moved,
and then No. 1 in its turn again; but observation inclines me rather
to decide that there is no other rule than the feeder’s individual
convenience, according to what its teeth may be grasping, any more than
there is in other creatures that without reflection or intent, and not
strictly in turn, eat now on one side of the mouth and now on the
other (except in the case of some poor mortal with the toothache, when,
having only the two jaws, his distressful efforts are chiefly directed
towards relieving that side of its ordinary duties). Snakes, for aught
we know, may have the toothache: loose teeth they frequently have; they
suffer from gum and mouth affections too, and no doubt can at such
times relieve a whole jaw of its work.
In all true snakes the teeth are long, conical, and curved: not planted
perpendicularly, but directed backwards; these long, fine, claw-shaped
instruments presenting a formidable obstacle against the retreat of a
creature once seized by them. Their arrangement is a species of trap,
like the wires of a mouse-trap: to enter being easy enough, but to
escape against the spikes being impossible.
All snakes renew their teeth throughout life. Except fishes, therefore,
no creatures are so abundantly supplied with teeth as are the Ophidia.
On account of this continual loss and replacement of teeth, the number
is rarely so fixed and determinate as to be characteristic of the
species. Probably no two snakes, not even brothers and sisters of the
same brood, may possess precisely the same number of teeth at a given
age; because they are so easily loosened and lost, that the normal
number might rarely occur in all the members of the same family at the
same time. In the scientific language of Rymer Jones, ‘the facility for
developing new tooth germs is unlimited, and the phenomena of dental
decadence and replacement are manifested in every period of life.’
Says Nicholson, ‘The teeth are replaced not merely when accident has
broken off the old ones, but they are all shed at more or less regular
intervals, coinciding with the casting of the epidermis.’ Not on _each
occasion_ of sloughing, as we may, I think, understand this, but, like
the casting of cuticle, contingently, according to the condition of the
individual. Not altogether, either, or at certain periods of life, as
a child loses his first teeth and gets a second crop, or as an adult
cuts his wisdom teeth, but ‘a crop of young teeth work their way into
the intervals of the old teeth, and gradually expel these latter.’ All
the spaces and depressions between the maxillary and palatine rows are
occupied by the matrix of tooth germs. Not a cut can be made in this
part of the palate without the knife turning up a number of young teeth
in every stage of development.[92]
Independently of this accidental number, the maxillary presents certain
phases which characterize families. For instance, a true viperine snake
has in the upper jaw fangs _only_: non-venomous snakes have a whole row
of from fifteen to twenty-five maxillary teeth, and in intermediate
species their normal numbers vary considerably. Some of the highly
poisonous families, notably the cobras and the sea snakes, have a few
simple teeth in addition to fangs. The length of the jaw, therefore,
diminishes in proportion to the number of teeth it bears. Only the
viperine snakes are limited to the poison fang in the upper jaw; but
fangs, like the simple teeth, are shed, broken, or lost, and renewed
continually.
Behind the one in use—the functional fang—others in various stages of
development are found—‘a perfect storehouse of new fangs,’ as Mr. F.
Buckland in his facetious style called them; ‘lying one behind another
like a row of pandean pipes.’ In the skeletons of viperine snakes these
may readily be observed. In the living example they are enclosed in a
capsule, hidden by the loose gum sheath, called a gingeval envelope. So
when the functional fang meets with an accident, or falls out in the
order of things, the supplementary fangs in turn supply its place, each
becoming in time firmly fixed to the jaw-bone, and ready to perform the
office of its predecessor.
Poison fangs succeed each other from behind, _forwards_; the simple
teeth from the inner side, _outwards_.
Before proceeding further, it may be well to explain that what is
meant by the _true_ snakes in the foregoing rules, are those which do
not possess the lizard features; _Anguis fragilis_, and some of the
burrowing snakes which approach the lizards, not having the palate
teeth. But here again we are tripped up with exceptions, since we are
told that in dentition the boas are allied to the lizards; yet they
have palate teeth.
The importance of dentition in distinguishing snakes is seen in the
names assigned to them from their teeth alone. In giving a few of these
terms we enable the reader to perceive at once, not only how very
varied are the systems of dentition, but in what way they vary, the
words themselves conveying the description.
The names here given are without reference to venomous or non-venomous
serpents, but only as belonging to certain families whose teeth present
characteristics sufficiently marked to be named by them.
From _odous_, _odontos_, a tooth.
Anodon, Toothless.
Boodon, Ox tooth.
Cynodon, Dog’s tooth.
Deirodon, Neck tooth.
Dinodon, Double tooth.
Glyphodon, Grooved or carved tooth.
Heterodon, Abnormal tooth.
Isodon, Equal toothed.
Lycodon, Wolf’s tooth.
Ogmodon, Furrowed or grooved tooth.
Oligodon, Few toothed.
Rachiodon, Spine toothed.
Sepedon, Noxious tooth, or a tooth causing putridity.
Tomodon, Stump tooth.
Xenodon, Strange tooth.
In Dumeril’s system very many families, including sometimes several of
the above, are grouped according to their teeth, thus:—
_Aglyphodontes_, Teeth not carved or notched.
_Holodontes_, Whole or entire teeth.
_Anholodontes_, Without whole or entire teeth.
_Aproterodontes_, Without front teeth.
_Isodontiens_, With even teeth.
_Apistoglyphes_, Grooved at the back, or the back teeth grooved.
_Proteroglyphes_, Grooved in front, or the front teeth grooved.
_Solenoglyphes_, Cut or carved with a canal.
And some others whose names are equally descriptive.
These various characters, with the exception of _Aproterodontes_, which
refers to the under jaw, have reference to the upper jaw only. It might
be tedious to the reader to enter into a minute description of each of
the above groups: sufficient for our present purpose is it to show that
such varieties exist, and that a simple, even row of teeth, as a family
distinction, is oftener the exception than the rule. Some of the teeth
increase in size posteriorly, others are largest anteriorly; others,
again, are larger towards the middle of the jaw, and decrease at either
end. Some harmless snakes have ‘fangs,’ that is to say, fang-like
teeth, but not connected with any poison gland, and at the back
instead of the front of the jaw. Again, there are some non-venomous
species that have the power of moving these fang-like teeth, raising
or depressing them as vipers move their fangs, and as will be further
described presently. Some grooved teeth convey an acrid saliva, others
are without any modification of saliva, the long teeth being of use in
holding thick-skinned prey.
Thus we find every gradation both in number and in form until we come
to the true fang, the ‘murderous tooth’ of the terrible cobra, the
_hydrophidæ_, and the _viperidæ_. And noteworthy it is that the fewer
the teeth in the maxillary bone the more terrible are they. Fig. A of
the four illustrations given opposite is the jaw-bone of the Indian
Rat snake, _Ptyas mucosus_, already ‘honourably mentioned’ in these
pages. The illustration being taken from Fayrer’s _Thanatophidia_,
may be received as a faithful representation. This conveys a good
idea of jaws generally in non-venomous snakes of that size, say from
six to ten feet long. In some of the smaller kinds the jaw and palate
teeth are so fine as to be almost imperceptible to the naked eye. To
the touch they feel like points of the finest pins. Draw your finger
along or press it against a row of ‘minikin pins,’ and you will form a
correct idea of these tiny weapons. I have often _felt_ when I could
not _see_ them in the mouth of a small harmless snake. Pass the tip of
your little finger gently along them towards the throat, and they are
almost imperceptible even to the touch; but in withdrawing your finger
_against_ the points, you feel how excessively fine they are.
The accompanying illustrations are from nature, and exemplify the
various lengths of jaw in four snakes, not differing very greatly in
size.
[Illustration: Four jaws. From Fayrer’s _Thanatophidia of India_.]
_Fig. A._ _Ptyas mucosus_, with simple teeth only. That they are not
very regular is probably owing to the stages of growth in those that
have replaced others.
_Fig. B._ A venomous snake, _Bungarus_, the ‘Krait,’ with a fixed fang
in front and a few simple teeth behind it.
_Fig. C._ Jaw of the cobra, with a longer fixed fang, and one or two
simple teeth behind it.
_Fig. D._ The shortest jaw of them all, that of the Indian viper
_Daboia_, in which the maxillary is reduced to a mere wedge of
bone. These, with four or five reserve fangs, are here folded back
‘depressed.’ A few palate teeth are also seen.
Having given a slight sketch of the various forms of dentition, and
arrived at ‘fangs,’ we may recapitulate, in what Nicholson calls
‘roughly speaking,’ four stages of development in these latter.
_First_, the ‘fangs’ of the harmless snakes, such as _Lycodon_,
_Xenodon_, _Heterodon_, etc., which have no poison gland, but whose
saliva may be slightly and occasionally injurious.
_Secondly_, those having a salivary gland secreting poison and a
grooved fang in front of some simple teeth, _Hydrophidæ_.
_Thirdly_, the maxillary bone shorter, bearing one poison fang with a
perfect canal, and one or two teeth behind it. In some of these there
is a slight mobility.
_Fourthly_, the maxillary bone so reduced as to be higher than long,
and bearing only a single tooth, viz. a long, curved, and very mobile
fang, _Viperina_.
These four classes, be it observed, are only designated ‘roughly
speaking.’ Nicholson describes a close gradation in the development of
the poison glands also to correspond with those almost imperceptible
stages. The poison gland is after all only a modified salivary gland.
It lies behind the eye, whence the venom is conveyed by a duct to the
base of the fang, down along it, and sometimes through it, and is
emitted at what we may for the present call the point, into the wound
made by it, something on the principle of an insect’s sting. As when
inserting the sting the pressure forces the poison out of a gland at
its base, so does the pressure of certain muscles act upon the poison
gland when a snake opens its mouth to strike. In some of the most
venomous, viz. the viperine families, the largely developed glands give
that peculiar breadth to the head. There is a hideous, repulsive look
about some of these, that seems to announce their deadly character,
even to those who see one for the first time. The evil expression of
the eye, with its linear pupil; the peculiar curve of the mouth, with
its very wide gape downwards, and then up again, are unmistakeably
treacherous, venomous, vicious.
Like all other animal secretions, the poison is produced, expended,
and renewed, but not always with equal rapidity; climate, season, and
temperature, as well as the vigour of the reptile, influencing this
secretion. The hotter the weather, the more active the serpent and all
its functions. When the poison gland is full and the snake angry, you
may see the venom exuding from the point of the fang, and by a forcible
expiration the reptile can eject it. I have seen this in the little
_Echis carinata_ and its congener the _Cerastes_. I am not certain
whether the _Cerastes_ hisses or not, but under terror or excitement
it moves itself about in ‘mystic coils’ as Echis does, producing a
similar rustling noise with its scales; but both of them, if angry,
will strike at you with a sound which may be compared with a sneeze or
a spit, at the same time _gnashing_ their mobile fangs and letting you
see that they have plenty of venom at your service. They may almost be
said to ‘spit’ at you, though literally it is the mouth ‘watering with
poison,’ combined with the natural impulse to strike, which produces
this effect. We can, however, by this judge of the force with which the
venom is expelled, which in a large viper must be considerable.
Travellers have told us that a serpent ‘spouts poison into your eye.’
If an angry one strike, but miss its aim, the poison is then seen to
fly from its mouth, sometimes to a distance of several feet. Whether a
snake is so good a marksman as to take certain aim with this terrible
projectile, or whether he possess sufficient intelligence to attempt
it, we may doubt. Dr. Andrew Smith tells us that this belief prevails
among the natives of South Africa.
A bright object always attracts snakes, and some victimized traveller’s
eyes may have been remarkably brilliant, and in consequence smarted
under the accident. Be that as it may, the poison is sometimes so
abundant that you may see it flow from the mouth over the prey. The
glands being excited, just as are the salivary glands of mammals, the
mouth ‘waters’ with poison. In the Hamadryad I have seen it flow, or
more correctly ‘dribble,’ down over the snake it was eating. This
noxious secretion assists digestion in the same way that the ordinary
saliva in the human mouth does. Says Dr. Carpenter, ‘The saliva
prepares food for the business of the stomach; and if the ordinary
operations of mastication and insalivation be neglected, the stomach
has to do the whole work of preparation as well as its own especial
duty of the digestion.’ That the digestive powers of snakes are strong,
we know from the fact that nearly all animal substances are converted
to nutriment in the stomach of a healthy snake. The abundant saliva
must be a powerful agent in the process, because mastication takes no
share in the work. This has become more than mere conjecture, since
recent experiments have shown that snake venom possesses strong peptic
qualities; that, like pancreatic juice, it will even dissolve raw meat
and albuminous substances. Recent experiments have also shown that
the salivary gland is the laboratory in which the poison of venomous
serpents is elaborated; that ordinary saliva is there intensified,
concentrated, and endowed with its toxic properties.
During the two hundred years that have witnessed the development of
natural history into a science, many and various have been the methods
of zoological and particularly of ophiological classification. A
few of these methods are sketched out in chap. ii. It will be seen
that the character of the teeth had not for a long while much weight
in classifying snakes. According to Schlegel, Klein in 1755 was
the first to separate the venomous from the non-venomous snakes in
classification. But after him Linnæus, then the greatest naturalist of
modern times, distinguished snakes chiefly by the form of the ventral
and sub-caudal plates; so that in the six genera which he established
(_Amphisbæna_, _Cecilia_, _Crotalus_, _Boa_, _Coluber_, and _Anguis_),
rattlesnakes and boas, colubers and vipers, with others of the most
opposite characters, were jumbled up together; and the little burrowing
blindworm and the venomous sea snakes were supposed to be related,
because they neither of them had ventral scales! On account of his
vast researches and great reputation, subsequent naturalists were slow
to entirely overthrow his system and to venture on reforms of their
own, and our cyclopedias are suffering to the present day from the
confusion of the various methods of classification adopted by so many
naturalists, as a few quotations presently will show. Dandin, 1802,
though his work was reckoned by Schlegel the most complete up to his
time, comprehended all the venomous snakes under the head of ‘vipers.’
Cuvier divided the vipers (with _crochets mobiles_) from those with
fixed fangs; but yet was unsound in many other respects, confounding
the _Elapidæ_ with the _Viperidæ_, although he professed to separate
them. Another confusion arose out of the word _cobra_, Portuguese
for snake, so that wherever the Portuguese settled most snakes were
_Cobras_. In India the English have retained the name _Cobra_ for the
snakes with the hood, which name is now confined to the one group,
_Capella_.
‘The characters of dentition offer in a great many cases a decisive
method for distinguishing the species,’ says Günther; ‘but as regards
the combination of species into genera and families, it is of no
greater importance than any other external character by itself....
Still I am always glad to use the dentition as one of the characters of
genera and species whenever possible—namely, whenever it corresponds
with the mode of life, the general habits, and the physiology.’[93]
Since the publication of Dr. Günther’s work, _The Reptiles of British
India_, 1864, the distinctions of the various types of dentition
seem to have been more clearly comprehended; and as this work is the
accepted authority among English ophiologists, and will best commend
itself to the reader, it shall be our guide in the present attempt to
simplify much complication.
The five groups of snakes described in chap. ii. are divided into three
sub-orders of Ophidia as follows:—1. _Ophidia colubriformes_ (the
harmless snakes). 2. _Ophidia colubriformes venenosi_ (those which, not
having the viperine aspect just now described, are the more dangerous
from their innocent appearance). 3. _Ophidia viperiformes_ (the
viperine snakes).
Although apparently named from their form only, it is the teeth which
have chiefly to do with these latter distinctions, as will be seen on
reference to the dotted examples of upper jaws. The first have the six
rows of simple teeth (four above, as seen, and the lower jaw teeth),
in all from 80 to 100 perhaps. The second have the two rows of palate
teeth, the lower jaw teeth, and a _fixed_ fang on each upper jaw, with
one, two, or more simple teeth in addition. The Australian poisonous
serpents are nearly all of this group, the only viperish-looking one,
the ‘Death adder,’ having fixed fangs like the cobras. The sea snakes
and the _Elapidæ_ are included. The third have only four rows of simple
teeth, viz. those of the lower jaws and those of the palate, with a
solitary moveable fang in each upper jaw.
[Illustration: From Fayrer’s _Thanatophidia_. The four larger dots
represent fangs.]
Fayrer divides the poisonous snakes of India, again, into four
families, viz. _Elapidæ_ and _Hydrophidæ_, with fixed fangs; and
_Viperidæ_ and _Crotalidæ_, with mobile fangs.
But without so many perplexing distinctions, I hope to be able to
interest the reader in that wonderful piece of mechanism, the poison
fang, and by the aid of the authorities to represent it in simple
language.
We have long been accustomed to read that a serpent’s fang is a
‘perforated tooth’ or a ‘hollow tube,’ as if a miniature tusk had a
hole bored through its entire length, the poison entering at the root
and flowing out again at the point. This is not strictly the case.
Fangs in their construction are not absolutely ‘hollow,’ with ivory on
the outside and pulp on the inside, but are as if you had flattened
out an ivory tusk and folded or wrapped it over again, so as to form a
pointed tube. It would then have dentine both on the outer and inner
surface. This involution may be compared with that seen in a long
narrow leaf, in which the larva of an insect has enwrapped itself. The
various degrees of involution are extremely close, as also would be
the forms of leaves and the extent of curling which each caterpillar
had effected. Some fangs are folded so as to leave the—_join_, we
will call it, easily perceptible. Others leave a groove more or
less evident; while in others the fold is so complete as to have
disappeared entirely. Schlegel, in describing the insensible passage
from solid teeth to fangs, affirms that traces of the groove are always
perceptible: ‘_On découvre toujours les traces de la fente qui réunit
les deux orifices pour le venin._’[94]
[Illustration: Two fangs magnified, showing the slit more or less
complete. _c_, a section. From Fayrer’s _Thanatophidia_.]
In a mixed collection of thirty odd fangs of various snakes lent to
me by Holland, the keeper, for examination, and sent all together in a
little box, there were few in which I could not discern the join. The
keeper was not sure to which snakes each belonged, excepting one or two
of the largest, which were those of a puff adder. Those of the larger
_Crotalidæ_ I could identify by the peculiar curve. In a functional
fang of the ‘bushmaster’ (_Lachesis mutus_), which I myself took from
its jaw, there is a well-defined line, like a crack, the whole way
down, from the base to the slit; in a rattlesnake fang, also in my
possession, there is a faint appearance of this line or join; and in a
young Crotalus fang it is still there,—only a faint crack, such as you
would contemplate with alarm in your egg-shell china, still there it is.
It is scarcely necessary to explain that fangs differ in size in
different families, as well as proportionately to the size of the
possessor. In sea snakes they are not much larger than the simple teeth
behind them. In the Cobra they are larger than in the Bungarus; in the
viper they attain their largest size.
But in one respect all fangs agree, and that is in their delicacy and
fineness. Under the microscope, the stronger the lens the greater the
degree of exquisite polish and sharpness revealed. To handle those
of very young vipers is as difficult as it would be to handle fine
needle-points of similar length. One can compare them with nothing
else, except perhaps the fine thorns of the sweet briar, which are
equally unmanageable, and, as compared with manufactured articles,
equally exquisite.
Sir Samuel Baker describes the fangs (both functional and
supplementary) of a puff adder which he found. His words, if not
strictly scientific, are so graphic as to convey a true idea of these
terrible weapons. The viper was five feet four inches long, and fifteen
inches in girth in its largest part. The head was two and a half inches
broad. Sir Samuel counted ‘eight teeth’ (fangs), and secured five of
them, the two most prominent being nearly one inch long. ‘The poison
fangs are artfully contrived, by some diabolical freak of nature, as
pointed tubes, through which the poison is injected into the base of
the wound inflicted. The extreme point of the fang is solid, and is so
finely sharpened that beneath a powerful microscope it is perfectly
smooth, although the point of the finest needle is rough!’[95] He
describes the aperture in the fang as like a tiny slit cut in a quill.
This ‘slit’ is a very important feature in the fang, and is the cause
of much trouble in deciding whether a bitten person has been poisoned
or not. It is in reality a very small space _near_ the point, where the
involution of the fang is incomplete, that is, where it has remained
unjoined. This is to permit the emission of the venom. It is not
close to the point, which, as Sir S. Baker affirms, is solid. Being
solid, it is stronger and sharper, penetrating the skin of the victim
more easily, and making way for the venom which in viperine fangs
then follows and escapes through the slit into the wound. By this we
comprehend how a person may receive a puncture only, or a scratch with
this extreme but solid point, but not deep enough for the poison to
enter. The space between the lines at _a_ in the next illustration
shows where this slit in the fang is found. In the larger fangs it
may be readily discerned with the naked eye: under a magnifying glass
it is distinguishable in all. It is distinct in the fangs of the young
Jararacas now before me, and extends nearly half-way up the fang in
these.
The examples of fangs here given are all from nature, and as near to
the exact size as it is possible to be in delineating objects of such
exceeding fineness and delicacy. Excepting the _Xenodon’s_ and the baby
viper’s, the others belong to the _Crotalidæ_, whose fangs are mostly
distinguishable by a slight double curve or flange. The viperine fang
is a continuous curve (see _f_), but in the _Crotalus_ the point curves
very slightly back again and downwards.
For the Brazilian specimens, I am indebted to Dr. Arthur Stradling, who
presented me with the snakes, out of whose jaws I myself procured them.
In this _Lachesis_ there were two fangs _visible_ on one side, and
only one on the other, viz. the functional pair, and one nearly ready
to replace one of these. In addition to the pair were four reserve
fangs hidden under the functional one on the right side. I say ‘under,’
because anatomically they were _beneath_, though locally _above_ when
the snake was in its natural position. All these five fangs I got from
only one side, and in addition some others too small to represent.
There may be yet more in the membranous capsule, as mine was a sadly
unscientific search for them, and without any very powerful magnifier.
Like Charas, I ‘grovelled’ for them! From a young _Jararaca_ I also got
out the functional and four or five supplementary fangs from one side,
also an exceedingly small and short jaw-bone, leaving the other side
undisturbed. Even the principal fang (_d_) is too fine to represent
faithfully in printer’s ink; the others are to the naked eye and to the
touch almost impalpable. When we reflect on the exquisite sharpness and
finish of these minute weapons, and the fatal injury they are capable
of inflicting, we are filled with awe and amazement at the virulence of
the subtle fluid which oozes through that almost invisible aperture.
The brother of this tiny African viper (_f_), when only a few hours
old, struck a mouse, which was dead in less than one minute. The whole
forty-six of them (p. 321) were born with the ‘murderous teeth’ in
their vicious little jaws. The fang here represented was loose in its
mouth. A pair of perfect functional fangs remained.
[Illustration: Fangs and some simple teeth from my specimens.
_a._ Functional fang and four supplementary fangs from _Lachesis
mutus_ (Brazil).
_b._ Rattlesnake fang.
_c._ Fang of young rattlesnake (Brazil).
_d._ Fang of young _Jararaca_ (Brazil).
_e._ Pseudo ‘fang’ of _Xenodon_ (Brazil).
_f._ Loose fang from the mouth of _Vipera nasicornis_, aged one week.
_g._ Portion of palate bone bearing four teeth, from _Lachesis mutus_
(Brazil).
_h._ Two lower teeth from the same.]
Picture to yourselves the intensity of that invisible molecule of
venom, which could ooze through an equally invisible aperture in this
last diminutive weapon, and be fatal to life in a minute of time! From
the effects observed on victims, I am inclined to place these large
African vipers amongst the most venomous of all serpents of their size.
It may be of interest to remark that the fang of the baby viper found
loose in its mouth does not resemble those remaining, either in form
or structure. That it cannot be a jaw tooth is evident from its size.
Jaw and palate teeth there are, but discernible only to the touch,
and under a magnifying glass. The fixed fang from the side on which
I found this loose one, is a trifle shorter, and much finer than its
fellow. In the loose one here given I can hardly discern any involution
at all, but on touching it with the inky point of a fine needle, the
stain shows it be hollow, and clearly so, at its base. In the two fixed
fangs, however, the involution is so incomplete that, minute as they
are, the point of a very fine needle can be drawn all down them without
slipping off.
One of them, the larger, on being touched with ink, revealed this
open groove or incomplete involution so distinctly that I tried the
other and was convinced at once. The loose one may be a first and
only half-developed fang. They are almost as transparent as glass. I
requested the keeper to look into the mouths of those subsequently
dead, but he found no other loose fangs. Of the remaining forty-five
deceased, let us hope those into whose hands they have fallen will be
able to throw some further light on the development of fangs in very
young vipers. Fayrer tells us that a young cobra is not venomous until
it has cast its first skin, which is usually within a fortnight. White
of Selborne found no trace of fangs in young vipers which he examined
with a lens; but these had not yet been born. The possible cause of
functional development in this little viper’s fangs may be found in
chap. xxiv. of this work.
Another erroneous impression regarding fangs has been produced by
confusing those that are ‘fixed’ and those that are ‘moveable.’ All
truly are fixed firmly into the jaw; but in the viperine snakes the
very short bone itself is moveable by a volitionary action, so that it
partially ‘rotates,’ and with it the fang. The _Elapidæ_ have fixed or
‘permanently erect’ fangs, and when the mouth is closed these fit into
a depression in the lower jaw. Viperine fangs only can be erected or
depressed at pleasure. It is those which spring into place for use like
a pen-knife half opened, and which when at rest are folded back, like
the knife shut up again. This action has been most lucidly described by
Coues in connection with the _Crotalidæ_, under which head I will quote
from his paper. Schlegel himself is not very clear in his distinctions
between those serpents that have ‘moveable’ fangs and those which have
not, but Cuvier had already described them as _crochets mobiles_.
Indeed, it is since the date of Schlegel’s work that more complete
investigations have revealed closer anatomical distinctions. We
therefore find in some of our highest-class encyclopedias, if not of
recent date, mis-statements regarding fangs which unfortunately have
been quoted in many works. ‘Venomous serpents depress their fangs,’
says Schlegel’s translator, true to the text, but as if it were common
to all. Describing deglutition, Schlegel says ‘the same in all’ ‘_sans
en excepter les venimeux, qui lors de cet acte redressent leur crochets
et les cachent dans la gaine des gencives, pour ne point les exposer
à des injures_.’[96] This, however, is the case with the _Viperina_
only. It is common, for the reasons just now assigned, to find the
cobra classed among the vipers, in some popular encyclopedias; and in
one, a valuable and generally trustworthy American edition of 1875, we
read, ‘moveable fangs like the cobra, viper, and rattlesnake.’ A cobra
has _not_ moveable fangs. Another, an excellent English edition, but of
not very recent date, includes _all_ venomous snakes under the head of
‘vipers;’ a third in general terms states that ‘venomous snakes have no
teeth in the upper jaws, excepting the fangs, and that the opening of
the mouth brings these into position;’ whereas it is now known that a
viper can open its mouth and yet keep its fangs depressed and sheathed.
In several other encyclopedias the description of fangs is suited to
vipers only.
It is not necessary to designate names, as these things will be set
right in the new editions. They are mentioned more with a view to
show that ophiology has advanced with rapid strides of late, rather
than presumptuously to criticise our standard works. Perhaps in
another twenty years my own poor efforts will be exposed as ‘old-time
misconceptions.’
The renewal of poison fangs is another subject of interest to
ophiologists: how the next supplementary fang becomes fixed,
_anchylosed_ to the jaw-bone; and how and when the connection with
the poison duct is completed. Mr. Tombes, in a paper read before the
Royal Society in 1875, describes a ‘scaffolding’ of bone thrown out
to meet and grasp the new fang, to ‘interdigitate and fix it in its
place; this soft bone rapidly developing and hardening.’ Sufficiently
marvellous is the functional fang in itself; the insertion of the
venom, a mode of subcutaneous injection invented long before the
doctors thought of it. ‘A most perfect hypodermic syringe,’ Huxley
calls it. Suddenly the hypodermic syringe is removed, say by accident,
by force, or by gradual decay, and all connection with the gland is cut
off; yet within a given period a second, a third, an unlimited number
in turn replace it: the connection is restored and the hypodermic
syringe is ready for action again. How the new one is brought into
relation with the poison duct has afforded much speculation, and
in the American scientific journals, as well as those of Europe,
papers on this subject appear from time to time. Dr. Weir Mitchell of
Philadelphia affirms that when the fang is lost by natural process
it is replaced in a few days: when by violence, several weeks elapse
before the next is firmly fixed.[97] He speaks of the rattlesnake
chiefly. Fayrer gives the periods in several cobra experiments. In one
cobra whose fangs were carefully drawn out on Oct. 7th, new fangs were
‘anchylosed’ to the bone in twenty-four days. In another, thirty-one
days elapsed before the new ones were ready for use; and in two others,
eighteen days. In all of these cases the new fangs were capable of
inflicting deadly injury by the time stated.
But the perfection of mechanism culminates in the viper fangs; and
reasoning from analogy, the intensity of poison in their glands also.
When at rest, these lie supine along the jaw, but can be ‘erected,’
_i.e._ sprung down, for use by a special muscle. The two fangs above
the dotted illustration of viperine dentition (p. 355) show both
positions. Nicholson affirms that the Indian viper Daboia can inject
as much poison in half a second as a cobra can in three seconds; ‘that
whereas a cobra’s virus flows in small droplets, the viper’s runs in
a fine stream.’ Though a much smaller snake than the cobra, Daboia’s
fangs are nearly double the size, as may be observed by comparing the
figs. _C_ and _D_ (p. 349). There seems reason to believe also that
this viper (which in its features Fayrer considers a true Indian type)
can inflict injury with more than the pair of functional fangs. ‘In
reference to the connection of the poison fangs with the maxillary
bones,’ says this learned experimentalist, ‘I would note that second
or even third supplementary fangs may be anchylosed with the principal
one to the maxillary bone. I have before me the skull of a Daboia, for
which I am indebted to Mr. Sceva, in which this is the case; and where
there are five well-developed poison fangs on each side, of which on
one side two are anchylosed to the bone.’[98] (Described by Mr. Tombes,
_Phil. Trans._ vol. clxvi. p. 146.)
This may explain what we so often read in the description of venomous
snakes found with two, three, or more fangs on each side. In my
_Lachesis_ two were distinctly visible before I began to dig for those
hidden in the loose membrane, of which there seemed an abundance, and
I am nearly certain that the second one had its own particular sheath.
The spirit in which the specimen had so long been immersed, as well as
my awkward probings, forbid me to speak with certainty regarding this
second sheath.
After one of his rattlesnake bites—twenty days after—Dr. Stradling
informed me by letter: ‘My little _durissus_ is shedding its skin; but
when that is over, I shall certainly examine its mouth. Now that my arm
is on the verge of ulceration, I find what I had not noticed before,
that each puncture is _double_—two large ones and a tiny second one,
about 1/12 inch behind each, standing out in black relief against the
scarlet skin.’
Neither of these experimentalists stated positively that the reserve
fangs were in connection with the duct, a phenomenon which I believe
is still unexplained. Fayrer removed the functional fangs from an
_Echis carinata_, and observed that there were no others fixed at the
time, though there were others loose in the mucous membrane. _On the
fifth day another pair were anchylosed and ready for use!_ As will be
presently seen, this little viper of sixteen or eighteen inches (almost
too small to recognise near the great python in the frontispiece),
displays corresponding vigour both in the potency of its venom and in
the renewal of its weapons.
From the foregoing illustrations of numerous pointed teeth, the
question might arise, ‘How are they disposed of when the mouth is
closed? and from the narrow space which is apparent in the flat head
of a snake, and the close fit of the jaws, how do the four or six rows
meet without interfering with each other?’ This difficulty is obviated
by the teeth _not_ closing one upon the other as ours do. Nor are the
palate teeth in the centre, or they would wound the upper part of the
trachea and the tongue sheath, which occupy considerable space. They
close down on each side of these organs. ‘Every relief on one surface
fits into a corresponding depression on the other surface, and accurate
apposition of every part is obtained,’ Nicholson explains to us. ‘The
four upper rows of teeth divide the roof into three parts, and the
lower jaw teeth fit between the upper maxillary and palatine teeth.’
There remains yet much more to describe in connection with the poison
fang, which might come in the present chapter; but as the two following
will treat of the _Viperidæ_ and the _Crotalidæ_—the dentition being
the same in both—the viperine fangs shall claim further space under
those heads. These three consecutive chapters, and also chap. xxii.
on some exceptional forms of dentition, must necessarily be somewhat
blended; but I divide them thus in order to present the distinct
families more clearly, and render the subject less tedious to the
reader.
[Illustration]
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