TRANSCRIBER'S NOTE
oe ligatures have been expanded.
The footnote in Paragraph #35 on page 69 (the only one in the book)
was moved to follow the paragraph from which it is referenced.
Eight pages of advertisements that preceded the title page have been
moved to the end of the book and placed before the two pages of
advertisements that closed the book.
Obvious typographical errors and punctuation errors have been
corrected after careful comparison with other occurrences within
the text and consultation of external sources.
More detail can be found at the end of the book.
[Illustration: THE HORSE'S MOUTH,
SHOWING THE AGE BY THE TEETH.]
THE HORSE'S MOUTH,
SHOWING THE AGE
BY
THE TEETH.
CONTAINING
A FULL DESCRIPTION OF THE PERIODS WHEN THE TEETH ARE CUT;
THE APPEARANCES THEY PRESENT;
THE TRICKS TO WHICH THEY ARE EXPOSED;
THE ECCENTRICITIES TO WHICH THEY ARE LIABLE;
AND
THE DISEASES TO WHICH THEY ARE SUBJECT.
BY
EDWARD MAYHEW, M. R. C. V. S.
DEDICATED, BY PERMISSION,
TO
THE PRESIDENT AND COUNCIL
OF
The Royal College of Veterinary Surgeons,
AND EMBELLISHED WITH
NUMEROUS COLOURED ENGRAVINGS FROM
DRAWINGS MADE EXPRESSLY FOR THE WORK, AND
TAKEN FROM AUTHENTICATED MOUTHS;
WITH
THIRTY-TWO WOOD-CUTS, ILLUSTRATIVE OF THE LETTER-PRESS.
FOURTH EDITION.
LONDON:
MESSRS. FORES, 41, PICCADILLY.
TO THE
PRESIDENT AND COUNCIL
OF THE
ROYAL COLLEGE OF VETERINARY SURGEONS,
THIS WORK
IS (BY PERMISSION) RESPECTFULLY DEDICATED,
BY THEIR OBLIGED AND
VERY OBEDIENT SERVANTS,
THE PUBLISHERS.
41, _Piccadilly_.
ILLUSTRATIONS.
COLOURED ENGRAVINGS.
Page.
Frontispiece--The Head of a Horse with the teeth exposed
Nine months old, and 2 years old 70
Three years old, and 3 years off 80
Rising 4 years, and 4 years old 82
Rising 5 years, and 5 years old 94
Five years off, and 6 years off 96
Seven years off, and 8 years off 104
Twelve years old, and 20 years old 112
Sixteen years old, and 30 years old 120
WOOD CUTS.
Section of an incisor tooth 21
Arrangement of the substances composing a molar tooth 26
View of a molar tooth 29
A permanent and temporary incisor tooth 48
Molar tooth about to be shed 62
Molar tooth recently cut 62
Table of the 3 year old incisor tooth 79
Table of the 3 year off incisor tooth 79
Tables of the incisor teeth at 4 years off 85
Tables and arrangement of the incisor teeth rising 5 years 92
Tables and arrangement of the incisor teeth at 5 years old 95
Tables and arrangement of the incisor teeth at 6 years old 99
Tables and arrangement of the incisor teeth at 7 years off 103
Tables of the incisor teeth at 8 years off 106
Tables of the incisor teeth at 9 years old 109
Tables of the incisor teeth at 10 years old 110
Tables of the incisor teeth at 12 years old 112
Tables of the incisor teeth at 14 years old 112
Tables of the incisor teeth at 16 years old 115
Tables and arrangement of the incisor teeth at 28 years old 119
Tables and arrangement of the incisor teeth at 29 years old 120
Tables of the incisor teeth at 30 years old 121
Irregularity in the growth of the corner incisor tooth 140
A parrot mouth 147
Changes caused by a diseased tooth 175
Mr. Gowing's tooth forceps 183
The lever to ditto 184
The forceps, fixed 185
Mr. Gowing's framed chisel 188
Mr. Gowing's guarded chisel 190
Mr. Gowing's repeller for the guarded chisel 191
Mr. Gowing's lateral repeller for the guarded chisel 193
CONTENTS.
Par. Page.
1. That the teeth of the horse denote the age of the
animal &c. 1
2. In every case the evidence of the teeth is secondary
to direct and substantiated testimony; &c. 3
3. Some of the causes which induce certain persons
to doubt &c. 4
4. The teeth more frequently contradict an arbitrary
calculation than disagree with fact. 7
5. For the security of the purchaser of a horse, not
connected with the turf, the teeth are a sufficient
guard, &c. 10
6. The description of the teeth &c. 14
7. The teeth are situated &c. 15
8. The teeth are organised, &c. 16
9. The horse possesses forty teeth, &c. 16
10. Three substances enter into the composition of the
horse's tooth. 18
11. The crusta petrosa &c. 18
12. The enamel &c. 20
13. The ivory &c. 20
14. The uses of the ivory, enamel, and crusta petrosa
&c. 22
15. The separate uses of the three component structures,
&c. 24
16. The various parts and peculiarities of form, &c. 32
17. There are infundibula also in the molar teeth, &c. 35
18. To distinguish an upper from a lower molar
tooth &c. 36
19. The teeth of the horse are very firmly implanted in
the jaws, &c. 37
20. The molars of the lower jaw are the active agents
of mastication, &c. 37
21. Provision has been made by Nature to meet the
wear to which the horse's teeth are subjected. 38
22. The cavity of the pulp &c. 42
23. Nature provides the horse with two sets of teeth. 43
24. To know the temporary from the permanent
teeth, &c. 46
25. To recognise a milk incisor tooth &c. 46
26. The permanent incisors are indicated by their
greater size, &c. 49
27. The temporary cannot be well distinguished from
the permanent molars, while the horse is alive. 51
28. The various points which denote youth &c. 52
29. The indications of age &c. 53
30. The incisor teeth in old age, &c. 54
31. Some judges depend upon the tushes as indicative
of the age, &c. 57
32. The wolf's teeth or eye teeth aid us in judging of
the age; &c. 59
33. The mode in which the horse cuts his teeth &c. 60
34. The manner of examining the teeth &c. 65
35. At birth &c. 69
36. At six weeks, &c. 69
37. At six months, &c. 69
38. At nine months old, the corner milk teeth are up,
but their edges do not yet meet. 70
39. At one year, &c. 70
40. At eighteen months, &c. 71
41. At two years old, there is a full mouth of milk
incisors, all of which show considerable wear. 71
42. At three years old, the centre horse teeth are well
up, and are distinguished by their size, shape,
and colour. 72
43. At three years off, the lateral milk teeth are shed,
and the permanent teeth are coming up. 80
44. When rising four years old the lateral horse teeth
are in the mouth, but their edges do not fairly
meet. 81
45. At four years, four pair of horse teeth are well up,
but the corner milk teeth are retained. 82
46. When rising five years old all the horse teeth are in
the mouth, but the corner teeth have yet to meet. 90
47. At five years old there is a full mouth of horse
incisors, all the edges of which fairly meet. 94
48. At five years off the corner teeth only show slight
wear, and the posterior margins are round. 95
49. At six years of age the corner teeth look more
firmly set, and their edges begin to be uneven; &c. 97
50. At seven years off, the corner teeth, without showing
age, exhibit further evidence of wear. 99
51. At eight years off, the gum of the lower corner tooth
has become square, and the lower tush blunt. 104
52. After the eighth year, &c. 106
53. At twelve years old, there may be tartar on the
lower tush. The teeth are longer, narrower, and
the enamel darker. 110
54. At sixteen years old, when the teeth are viewed
from the side, only two incisors can be seen in the
lower jaw, &c. 112
55. At twenty years old, the form of the mouth has
changed, and the lower teeth are imperfectly seen
from the front. 115
56. At thirty years old, the jaws are contracted; the
lower are not seen when the upper teeth are in
view. 117
57. The tricks that are practised on the teeth, &c. 123
58. The irregularities of growth in the horse's teeth &c. 138
59. The diseases to which the teeth of the horse are
subjected, &c. 149
60. The agents which are likely to injure the teeth, &c. 177
61. The instruments used in connexion with the teeth
of the horse &c. 181
PREFACE.
When submitting to the reader this my first work on Veterinary Science,
I cannot forbear from addressing to him a few remarks, in the hope of
explaining some of those peculiarities which it may appear to present.
At a period of life, when many men retire from active business, I
commenced the study of a new profession. My mind was not prepared to
receive instruction through the ordinary process, and I was, by
necessity, obliged to be, in a great measure, my own tutor. I found that
I could learn only through observation, and this circumstance led me
into inquiries which often left me in opposition with established
opinions. Hence many of the facts announced in the following pages are
new, and not very much contained in them is strictly accordant with the
acknowledged authorities. The latter circumstance I may regret, but I
have no apology to offer for it. My convictions are derived from the
study of Nature, and are conclusions gained from a higher source than
conjecture or opinion sanctioned by time or approved by professors.
Short as may have been my experience, nothing herein set down will be
found which is not the result of practice, or the consequence of
reasoning. Perhaps a longer professional existence would have given more
weight to that which is either novel in its announcement, or may appear
to be bold in its assurance. Truth, however, is speedily read by those
who are intent on deciphering it, and facts are not rendered more clear
to the mental vision by years of conventional dependence.
The teaching of our English Veterinary School has, for too long a
period, been traditional; what one had said, he who succeeded him
repeated, and when I entered as a pupil, there existed no spirit of
inquiry, or thought of extending the boundaries of knowledge. To what a
degree an evil system had been established, I may here state as an
instance, that in the first horse which I dissected, I was able to
demonstrate the existence of four muscles that had previously been
unnoticed by my teachers.
Under such circumstances, it is not surprising if a fresh intruder, on a
comparatively unexplored soil, did turn up something which, though it
laid near to the surface, had not before been exposed. On the teeth, my
investigations began from the beginning; and though I cannot but say I
have been greatly assisted by the information derived from the labours
of previous writers, yet I have, in every instance, accepted their
assertions only after I had tested them, and found them to be correct.
To the members of my profession, I am deeply indebted. When they knew
the subject on which I was engaged, each volunteered to aid me, and
generously gave me the benefit of that experience, which personally I
was unfortunate in not possessing. It was acknowledged, that upon the
teeth, some work which might be depended upon, was sadly needed, and to
render the present worthy of the confidence of the public, all to whom I
applied cheerfully gave their utmost help. From their cordial
communications and disinterested co-operation, I learnt much, and gained
many valuable ideas.
_16, Spring Street,_
_Westbourne Terrace._
THE HORSE'S MOUTH,
SHOWING THE AGE
BY
THE TEETH.
1. _That the teeth of the horse denoted the age of the animal_ appears
to have been a very ancient belief, which the experience of centuries
seems in no degree to have weakened. As a general rule, applied within
certain limitations, the impression is certainly well founded; for
perhaps no development is more regular than the teeth of the horse, and
no natural process so little exposed to the distortions of artifice. We
are, nevertheless, not to expect that the animal carries about in its
mouth a certificate of birth, written in characters so deep or legible
that they cannot be obliterated or misinterpreted. The indications to
be discovered by an inspection of the mouth of the horse, however, are
so generally true, that in these dependence may be placed; although they
are not so arbitrary or invariable, that upon them in every instance an
absolute opinion can hastily be pronounced. He who would judge of the
age by the teeth, must therefore be content to study and prepared to
encounter difficulties. In proportion as he has done the one, and is
fortified thereby to overcome the other, will be his success. There is
no secret charm which will enable man to unravel Nature's mysteries. Her
ways are regular, but they are not uniform--her laws are fixed, but her
acts cannot be measured by a system of rule or compass. The qualified
judge alone will read the teeth correctly; but in proportion as the task
is difficult, will be the candour and caution of him who fulfils it
properly. He will make allowance where certain marks are indistinct or
absent--he will not feel himself degraded by a confession of inability
to speak with certainty when the signs are complex or confused--and
above all, he will be cautious before he pronounces a final opinion, and
gives it forth as a decision, against which there ought to be no
appeal. The Veterinary Practitioner knows from repeated trials, tested
by long experience, that the teeth of the horse are worthy of attention;
he feels that their indications, scientifically interpreted, will seldom
mislead; but he does not regard them with a reverence resembling that
originating from an antiquated superstition, or look upon them as the
exemplifications of a principle which admits of no exceptions.
2. _In every case the evidence of the teeth is secondary to direct and
substantiated testimony_; for as there is no limit to possibility, so no
man can be prepared to say what Nature may or may not do. In the
absence, however, of positive and corroborated testimony, the teeth
become the best evidence, and that on which reliance should be placed.
When opposed to the indications of the mouth, the oath of a single
individual, for obvious reasons, would be of no weight. A foal can
hardly be born without many parties being cognizant of the fact--the
colt cannot change its master without several persons being made aware
of the transaction--and horses, for honest purposes, are not generally
sold or bought in secret. Proof of the age can generally be adduced, if
the parties interested think proper to seek it; or when it is not
possible to adduce such proof, the teeth deserve more confidence than an
uncorroborated assertion. An individual may be interested to mis-state,
or may be mistaken in his belief; whereas the teeth, being natural
growths, are removed from such suspicions.
3. _Some of the causes which induce certain persons to doubt_ the
possibility of the horse's age being accurately told from the teeth, are
not difficult to explain away. The Jockey Club has seen reason to
declare, that all thorough-bred animals shall be born on the 1st of
January, or if any should make their appearances at a later period, such
shall be esteemed one year old when the 31st of December has expired.
All blood horses have but one birth-day, nor do they in that respect
differ from their brethren of the coarser breeds; only those of the last
description are supposed to begin their existences upon the 1st of May.
If a racer has seen six Januaries, it is said to be six years old; and
if a nag had looked upon half a dozen Mays it would be pronounced to be
of a similar age. These customs are convenient, as affording a point
from which to date the age of an animal; but under such regulations,
confusion will and does frequently arise. In a long number of years, a
few months may be of little importance; but at the earlier period the
difference of several weeks may, in the calculation of the age, be a
serious matter. I will endeavour to show how far, in an extreme case,
confusion may be created by the operation of these customs, and to
prove, that he who should read the teeth correctly, would be unable to
satisfactorily pronounce the accepted age of a colt. According to the
received laws, a blood foal dropt on the 31st of December, and a foal
not thorough-bred, born on the 30th of April, would each, the second day
of life, complete the first year of its existence. Let it be supposed
that a blood mare bore a foal in the latter end of December--the animal
would be entered in the stud book according to the year of its birth,
but for obvious reasons could never be put into training; it would be
kept until another January arrived, when, although but one year and a
few days of age, it could, in strict accordance with the established
custom, be sold as a two-year-old; and the entry being in the stud book,
of course the point would not be disputed. The colt is bought and taken
into an ordinary stable, where all the horses not being thorough-bred
advance a year when the 1st of May appears; and when that day dawns, the
blood colt, not eighteen months of age, rising with the rest, is called
three years off. Now in such a case, the man who judged by the teeth
would be certain to be wrong; and if it is possible under any
circumstances for truth to be discredited, we may imagine that many
apparent mistakes would, on inquiry, be cleared up. The age of a horse
is seldom correctly stated even in a court of law. Witnesses swear by
the customs of men, and it never seems to occur to them that Nature has
not yet given in her adherence to the codes by which their consciences
are narcotized. Horses are born at all times and seasons. The regular
breeder, it is true, takes care towards the observance of the
regulations; but all who may think proper to have "a foal out of the old
mare when she's done up for work," are by no means nice in that
particular. Stallions are paraded for "service" in the autumn, and there
are to be found men who will argue stoutly in favour of a "late get."
4. _The teeth more frequently contradict an arbitrary calculation than
disagree with fact._ The mouth declares only the positive age, reckoned
from the actual day of birth, and I know of no evidence of a similar
description which may be more confidently trusted. Occasional exceptions
are to be found, and of these notice will be hereafter taken; such
exceptions, however, are not sufficiently frequent to upset the rule,
and were the testimony of the teeth to be rejected, I know of no other
that could be substituted. We are therefore necessitated to retain the
test, and consequently should know how to apply it. Almost every one
within or about the stable pretends to be able to do this, but some even
of those who have studied the subject are not capable of doing it
correctly. The evidence is often true when the judgment is false, and in
this circumstance, perhaps, lies the chief danger of the test. A
knowledge of the teeth is by no means universal; but where that
knowledge is profound, though the test may seldom disappoint, yet
because it will occasionally do so, the indications of the mouth ought
to be corroborated. To proceed summarily (as in the case of the Queen of
Cyprus) upon an inspection of the teeth, is certainly not justifiable,
since the mouth may possibly be eccentric, or the judgment pronounced
upon it may be erroneous. The teeth in every horse case are of
importance. The suggestions to which they give rise should not be
disregarded; yet at the same time no opinion of a final kind should be
based upon their showing. The utmost that the inspection of the teeth
could warrant is a doubt, certainly a strong one, as to the reported age
of the animal. That doubt would justify inquiry, and the teeth can
substantiate no more than the right to inquire. Some may be disposed to
think that such a right would not be worth possessing; but it must be
remembered, that until the inquiry were ended, no decision as to the
qualification of the animal could be arrived at. A valid doubt would
have been created. Let the owner of the suspected horse dispel it, or
the party who is interested to do so have time to seek the evidence
which would convert it into certainty. The umpire, on the showing of the
teeth, would be bound to withhold his judgment, not called upon to
decide. Were such the rule, all fear of injustice would be guarded
against; and as gentlemen connected with the turf cannot endure
suspicion, and are not very patient of delay, those who were the owners
of animals, the mouths of which presented any peculiarities, ought to
notify the fact some days before the horses started. By forbearing to do
so, gentlemen expose themselves to accusation. By examining the animal
at the moment of starting, and founding a decision thereon, no good can
be done, but injustice may be perpetrated; for supposing the suspected
horse is pronounced to exhibit the tokens of the lawful age, the
inspection of its mouth by a stranger may, by exciting its irritability,
lose the race. At the same time, to permit an unqualified animal to
start, would be unjust; and therefore the greater necessity for such a
timely inspection as would allow of a preliminary investigation of the
proofs that could be brought forward in contradiction of the teeth.
These suggestions are made with the less hesitation, as the writer feels
that were they adopted, few cases would spring out of them; for the
mouths of racers are so regular in their development, that the age of
this description of animal can with more certainty be pronounced than
that of any other kind of horse.
5. _For the security of the purchaser of a horse not connected with the
turf, the teeth are a sufficient guard_, and their indications, when
properly understood, may be confidently acted upon. This opinion is put
forth after a matured consideration of the subject, and probably there
is no dealer who would dissent from the decision at which the author has
arrived. The purchasers possibly may, on reflection, see less reason to
be satisfied, because the teeth would, perhaps, in many instances, seem
to favour the interest opposed to theirs. Let the matter, however, be
deliberately weighed, and perhaps it may be found that neither party is
likely to gain considerably, or to be seriously injured. In ordinary
trade, the word of the seller is not much regarded; but in horse
transactions, the assertion of the dealer is never received. One source
of evidence is therefore discarded, and some other must be sought. Now,
where horses are concerned, even the oaths of men appear to be of little
force; "hard" swearing is expected in every business of that nature, and
such expectation almost disqualifies all those persons to whose
testimony the dealer could appeal. Let it be remembered that it is not
the dealer who refuses to give evidence, or to adduce it; but the
purchaser, who is prejudiced against accepting it. This act on the
purchaser's part limits the proof he might demand; for as attestation is
rejected by him, not denied to him, he is by his conduct left without
cause of complaint, and bound to seek the evidence which he will accept.
Such evidence he looks for in the mouth of the animal, and is seldom
deceived when capable of interpreting it. The teeth, in fact, are the
only testimony that his caution leaves him to decide upon; and it will
be hereafter shown, that even when the teeth are early in their
development, the purchaser is not virtually wronged. All men, however,
seek to arm themselves by suspicion, when dealing in horse-flesh; and
the tricks that are played upon the teeth, rise immediately to the mind.
Such tricks certainly are played, but they are assuredly more talked
about than practised. There is a superstitious idea afloat, that
breeders can make horses appear of any age they please, by torturing the
mouths of the poor animals. The folly of such a belief will be exposed
in another part of this work; it is sufficient for the present to state,
that the credulity of the public in this matter has no foundation. A
colt cannot be made by any barbarity to look like a horse; and an old
horse cannot be forced to exhibit the mouth of a colt. That attempts are
made to disguise the teeth, and that such attempts occasionally impose
upon the buyer, is not denied; but all of such practices are shallow in
the extreme, and so easily detected, that the person deceived by them is
not an object of pity. If people will presume to judge before they have
learnt to recognize, their temerity is more to be blamed than its
consequence is to be commiserated. No one goes to buy a horse unwarned
of the dangers that will surround him; and if in his conceit he rather
prefers to hazard these than to seek protection, what right has he to
murmur at a result which it needed no conjurer to foretell? Is there any
market in the world where ignorance is secure from imposition? The world
is not yet so honest that the affairs of the horse mart are a subject
worthy of its special wonder; and it may be doubted if the principles
which regulate the conduct of the horse dealer, are not those which
influence the transactions of the most honourable traders. There are men
of the highest character living by the sale of horses; and it is
creditable to humanity, that after all of a certain class have been
unscrupulously stigmatized and openly reproached, there may still among
its members be found, beings preserving honour for the sake of itself
alone. The liberal public, however, in its wisdom, has pronounced the
character of the horse dealer; it has rejected his attestations, and
refused to listen to the testimony of those with whom he has
communication. The age of a horse is not taken from the mouth of its
owner, but looked for in that of the animal. This mode of procedure is
convenient--the record is at hand, the evidence brief, and the decision
to which it leads is that to which the purchaser by choice appeals. The
dealer stands by and knows that his voice is to be restrained. The teeth
denote the age, and when the word of the owner is not to be accepted,
there is no other evidence at hand. Were additional proof to be
required, in some instances it could not be procured, and in the
majority its production would be attended with an expense perhaps equal
to the price of the horse which it concerned. The expence, the seller of
course could not be expected to bear, and the buyer equally would resist
its infliction. Nothing is more high priced than absolute proof of any
kind; and there is always a further difficulty in the difference of
opinion which prevails, as to what constitutes absolute proof. A cursory
glance at the matter is enough to convince us, that the custom of
inspecting the teeth of the horse to ascertain the age of the animal, is
one which has had its origin in necessity. Experience has taught that
the mouth of the horse affords the most satisfactory evidence, and the
author's investigations on this subject have convinced him that the
public need require no better or more conclusive testimony. The reader,
however, before he ventures to abide by his own interpretation of the
signs which the horse's teeth exhibit, must be content to study, and
prepared to find the task somewhat difficult. All that can be done to
render the subject plain and clear, the author will attempt.
6. _The description of the teeth_ cannot be rendered pleasing; but as it
is a necessary part of the subject, the reader must exert his patience,
while the matter is briefly discussed. Teeth are anatomically classed
with bones, which in many respects they resemble. A tooth is divided
into two parts, or into _crown_ and _fang_. The _crown_ is that portion
which projects above the gum into the mouth; therefore so much as can
be seen while the animal lives, is the crown of the tooth. The _fang_,
the end of which is called the _root_, is that part of the tooth which
is hidden from view, and is inserted into the jaw. For the convenience
of description, however, other portions of the tooth have received
distinct names, and the _neck_ and _table_ are spoken of. The neck is
that portion of the tooth which is immediately surrounded by the gum.
The _table_ is the upper surface, or the part which touches the
corresponding tooth of the opposing jaw when the mouth is closed. Such
is the division made, and it will hereafter be found to assist the
description of the various changes which the teeth undergo.
7. _The teeth are situated_ in the maxillary bones, in which certain
osseous cups, like indentations or holes, called the alveolar cavities,
are developed for their reception. Each tooth has its separate cavity,
and however close the crowns may appear, nevertheless each fang is
divided from those before and behind by bony plates. The alveolar cavity
always corresponds to the fang. As the fang alters in form, or
diminishes in length, so does the shape of the cavity simultaneously
change; and should the tooth be removed, the space, no longer needed, is
filled up; the alveolar cavity being obliterated by a growth of bony
matter.
8. _Teeth are organised_, that is, they possess nerves, arteries, veins,
and absorbents, or are endowed with those vessels needed to resist
decay, and to promote nutrition. That a tooth possesses nerves, no one
who has submitted to have these members filed by the dentist, or who has
endured the tooth-ache, can for an instant doubt; and that they are
even, in some degree, susceptible of external impressions, the sensation
produced by certain acids seems to render probable. The growth they
exhibit shows they are gifted with arteries and veins; and these vessels
can be traced directly to and from, though not unto, their substance.
The existence of absorbents some have doubted; but the removal by nature
of the fangs of the temporary teeth, clearly testifies the presence of
these vessels.
9. _The horse possesses forty teeth_, viz., twelve incisors, four
tushes, and twenty-four molars. The _incisors_, sometimes called
_nippers_, are those which, situated in front of the mouth, are seen
when the lips are parted. They are the instruments, by means of which
the animal bites its food, and are placed six in the upper, and six in
the lower jaw. They are classed as pairs, being generally cut or
developed after that fashion. The middle two, in both jaws, are called
the _centre_ incisors; the two most backward, on either side of the
mouth, the _corner_ incisors; and the teeth, by which the corners and
centres are separated, the _lateral_ incisors. Of the _tushes_, the two
placed in the lower jaw are the most forward. These teeth, which are
sometimes termed canines, and sometimes cuspidati, (from _cuspis_, a
point,) are isolated, appearing in the space which divides the incisors
from the molars. They are only fully developed in the male, the mare
often being without any indication of them, and never displaying them in
so prominent a degree as the horse. Their use is not very apparent, but
they certainly would be employed in those combats to which stallions
seem naturally predisposed, and would render the grasp, and the wound it
could inflict, more severe. Because the mare is of a more pacific
temperament, Nature seems to have denied to her a perfect tush, by the
presence or absence of which, the sex is indicated by the mouth, and
upon which castration appears to exercise no influence, since the
gelding has as well-formed a tush as the perfect male. The _molars_ are
ranged in companies of six, one company on either side of the upper, and
a like number similarly situated in the lower jaw. The molars are the
instruments which enable the horse to grind down the fibrous and hard
food upon which it subsists, and they are distinguished by their
locality, as first, second, third, fourth, fifth, or sixth molar tooth
of the near or off side in the upper or lower jaw; the first being that
growing in front, or nearest to the incisors, and the sixth that placed
most backward in the cavity of the mouth.
10. _Three substances enter into the composition of the horse's tooth._
Each of these substances is distinct, and can be distinguished from
either of the others. The names given to the various parts are--1,
crusta petrosa, or hard crust; 2, enamel; and 3, ivory.
11. _The crusta petrosa_ is the most externally situated, and when the
tooth first appears in the mouth, it is entirely coated by this
substance, having a somewhat dull and dark appearance, which is only
lost when the hard crust is removed by attrition, and the enamel thereby
exposed. In amount, the crusta petrosa is second to the ivory, being
more in quantity than the enamel. In composition, it is characterized by
containing a great amount of animal substance; and, in structure, it is
peculiar for exhibiting, under the microscope, numerous corpuscles or
cells, from which pores or minute tubes appear to radiate. Within the
alveolar cavity, the crusta petrosa, which around the fang becomes of
considerable thickness, is of a yellowish white colour; but where, in
connexion with the crown of the tooth, it is exposed to the chemical
action of the food and air, it presents a darker aspect and looks like
an accumulation of tartar, for which indeed it has been mistaken. It
fills up the infundibula of the molars of the upper jaw, and lines those
of the incisors, being pierced by all the vessels which nourish the
teeth. If a tooth be subjected to the action of dilute hydrochloric
acid, the enamel will be removed, and the ivory and crusta petrosa be
rendered separate and distinct.
12. _The enamel_ of the horse's tooth appears to be unorganized, and to
contain no animal matter. Hydrochloric acid entirely dissolves it with a
slight effervescence, and though a few and a very few threads remain,
these rather seem to be connexions between the ivory and crusta petrosa,
than component parts of the enamel itself. That the enamel is an
unorganized substance, it may be essential to state, is asserted only of
this body in the tooth of the horse; for the enamel of the cow's tooth
is of a different nature, since hydrochloric acid does not dissolve it,
affect its whiteness, or destroy its form. The enamel is the least of
the three components of the tooth; of a whitish semi-transparent shining
aspect, it forms a thin crust to the ivory, lying immediately under the
crusta petrosa, and extending nearly to the root.
13. _The ivory_ forms the main bulk of the tooth, and though blood
vessels can be traced to, but not within its substance, yet it presents
numerous pores or minute canals, radiating from the centre to the
circumference, which the mind naturally associates with nutrition. These
pores cannot be traced to the cells or corpuscles of the crusta
petrosa, though in works of high authority, drawings obviously
indicating such a connexion, are presented; they are limited to the
ivory, and terminate within it. What their exact use may be, is not
known, but that they are of service, their presence is sufficient proof.
Like the minute canals of bone, they probably convey a serous or
colourless fluid, for the nutrition of the part in which they are
developed.
[Illustration]
The relative positions of the various structures that enter into the
composition of the incisor tooth, will be better understood by
reference to the accompanying wood-cut, which represents one of those
members divided down its centre:--_a_ indicates the crusta petrosa,
which can be traced to enclose the organ, and to dip down the
infundibulum B. The crusta petrosa is shown to be thicker at the root of
the fang, and at the base of the infundibulum, than at other parts. _b_
denotes the ivory, which forms the principal and central portion of the
tooth, in the middle of which is the darker space marked by the letter
_d_. This last is intended to represent the cavity of the pulp, which,
in the young incisor is, as in the diagram, of great length. Between the
ivory _b_, and the crusta petrosa _a_, is a white line _c_, which
indicates the position of the enamel, and will be seen to cover the
upper surface of the tooth dipping into the infundibulum, but not to
extend quite to the root.
14. _The uses of the ivory, enamel, and crusta petrosa_ must be now
noticed. The ivory is less dense than the enamel, and harder than the
crusta petrosa. On the external surface of the incisor teeth, the crusta
petrosa is, by the attrition to which this part must be subjected during
the gathering of the food, soon sufficiently removed to expose a
portion of the enamel: as the years of the animal increase, the outer
coating is almost worn away, and not being reproduced, little of the
crusta petrosa will be found on the nippers of very old horses. The
ivory, however, is always nearly on a level with the enamel,
notwithstanding the greater attrition which the substance forming the
principal portion of the table of the tooth must necessarily endure. A
sufficient indentation of the ivory, nevertheless, can be observed, to
render prominent the ridge of enamel, and to indicate that the
last-named material is endowed with the greatest power of resistance.
The enamel, in fact, is as hard as flint, and by striking it against a
steel, fire can be drawn forth. The three structures, therefore, vary in
hardness, and in an opposite direction they contrast to one another in
toughness. The ivory is sometimes fractured, but not frequently. I have
never seen the crusta petrosa of a living tooth exhibit such an injury;
but the enamel is rarely inspected without its being discovered to be
more or less in a ragged, chipped, and broken condition, especially at
the anterior edge of the table of the incisors.
15. _The separate uses of the three component structures_, however, is
not well shown in the incisors; for as the crusta petrosa is by a
natural process removed, and the ivory is not of essential service in
cutting the food, it might be supposed that the first was no more than a
temporary covering to, and the last only a basement for, the enamel.
When the mind, however, is directed to the observation of the molars or
double teeth, the properties and uses of all become apparent. The sense
of touch in the horse resides in the lips; with those organs he gathers
together the food before he grasps it with the incisors. Delicate,
however, as the animal's sense of touch is, the selection of the food is
further aided by the sight and smell. The most fragrant, the softest,
and the cleanest portions, therefore, are selected; but it would be too
much to suppose, that no particle of dirt, sand, or grit, was ever taken
into the mouth. That much is necessarily bitten, the incisors of those
horses which pasture on sandy soils, afford sufficient proof, as such
animals generally exhibit the anterior edges of those teeth considerably
jagged or notched. In the best fields, the grass is never free from
adherent impurities, and the manger, as well as the rack, is not always
remarkable in that respect. All, however, that is gathered by the lips,
or grasped by the incisors, passes to the molars to be comminuted and
mixed with the saliva previous to being swallowed. The molars, in fact,
are animal grindstones, and the different degrees of hardness which the
three component substances display, by wearing unevenly, always keep the
grinding surfaces irregular or sharp. The inequality of the grinding
surfaces of the molars enables the horse to reduce the toughest fibre to
a pulpy mass; but as many substances little less hard than the tooth
itself must frequently be ground up with the food, the molars would, at
first sight, appear to be subject to injury, especially as they have ten
times the work of the incisors to perform, and the senses of touch,
smell, and sight, cannot operate for their protection. Nature, however,
has provided against the danger to which they appear to be exposed; for
if, notwithstanding the guarding agency of the senses, the incisors are
so often injured, the molars, blindly employed, and used when the full
power of the horse's jaw is exerted, certainly needed some provision
against fracture. The crusta petrosa gives all the security that could
be desired; it encircles these teeth, dips into their fissures, and
fills their infundibula, forming no small part of the substance of the
molars. The subjoined wood-cut will better explain the manner in which
the various substances are arranged.
[Illustration: _Fig._ 1.]
[Illustration: _Fig._ 2.]
_Figure_ 1 represents the table of one of the molars taken from the
upper jaw. _Figure_ 2 the table of a molar extracted from the lower jaw.
The difference of size between the two organs is thus well marked, as
also the difference of shape. The white line indicates the enamel, and
the variegated substance which is encircled by it, denotes the
comparative quantity and position of the ivory. The crusta petrosa is
represented by the somewhat darker shade situated on the exterior of the
enamel. In figure 1, however, the reader will observe two patches
enclosed by white lines. These are the representatives of the two
infundibula which exist in all of the molars of the upper jaw, but which
are not developed in the lower teeth. The similar direction of the lines
will enable the reader to connect them with the crusta petrosa, which
substance, save in the newly-cut tooth, generally fills up these
cavities, although the enamel lining extends almost to the root. The
intricacy of the arrangement is, by this diagram, made apparent, and the
purpose rendered plain. Without such a provision, the first meal of the
animal consumed would probably shatter the instruments of mastication
into innumerable atoms; but girded round, and bound up with the tough
and resistant crusta petrosa, however hard may be the fibre the animal
chews--however much of grit or sand may be contained in it--or however
great may be the force by which the molars are pressed together, and
made to pass at the same time from side to side--not a particle of the
brittle enamel is fractured. Like a thin layer of glass, guarded between
two pieces of wood, it performs its office in security; and as the
necessity for the provision, towards which I have directed attention,
is obvious, so is it the more strange that the thick coating of the
crusta petrosa around the molars should by authors have been mistaken
for an accumulation of tartar. The mistake was certainly extraordinary,
as the crusta petrosa in the horse's tooth is of physiological
importance, and will presently be shown to merit the attention of the
pathologist. I am aware, when making this statement, that contradiction
is offered to the opinions of many and deservedly esteemed authorities;
and while I regret the necessity of differing with such writers, I also
lament that my opinion as to the supposed use of the outer membrane of
the newly-developed organ, does not coincide with theirs. The nature of
this treatise will not allow me to enter into the subject of the
development of the teeth; but I may here say, that the outer membrane
has been generally stated to secrete the enamel. It is that membrane
which, thickening with the growth of the tooth, becomes the crusta
petrosa; but with regard to its secretive powers, I do not imagine it is
endowed with any function of that description, or that it is in any way
concerned in the production of the enamel. My reasons for making such
and so bold an assertion are well considered, not hastily advanced. I
have before me the left anterior molar, taken from the jaw of a colt
which was rising four. A representation of the tooth alluded to is here
given.
[Illustration]
_a_ denotes the crusta petrosa, _b_ the outer surface of the enamel, the
lines representing the plated or finely grooved aspect, which this part
exhibits on its exterior. _c_, which letter will, on inspection, be
discovered in the centre of the darkened space to the right of the lower
portion of the enamel, indicates a spot where disease was existing, and
to which reference will be hereafter made. _d_ denotes the roots, which,
as will be seen, are (although the tooth had been in active employment
for twelve months) still incomplete, and not enveloped by crusta
petrosa. The above wood-cut, the accuracy of which is not to be
disputed, shows a comparatively large portion of the assumed secretive
membrane to be absent. The deficient part of the outer covering, I may
here state, was removed by a natural process, as I myself extracted the
tooth. Nevertheless where the crusta petrosa is deficient, the laminated
external surface of the enamel is exposed in perfect and normal
condition. This evidence appears pretty conclusive, for where the
secretive substance is absent, the secretion would hardly appear. On the
other hand, if the secretion of the enamel were the special function of
the crusta petrosa, then wherever the one was found, the other would
also be present. Let the reader, however, refer to the wood-cut inserted
at page 21. In that diagram, the crusta petrosa is faithfully
represented as thickest at the root; but at this very point the enamel
is seen to be entirely wanting. The conclusion towards which such facts
point, is almost decisive; but, nevertheless, there are many inferences
which help to support it. If a longitudinal section of a tooth be made,
a very thin white line may be plainly seen, indicating, probably
between the ivory and the enamel, another source for the production of
the substance which the crusta petrosa has been said to secrete.
Moreover, if a tooth be boiled for some hours, a very little force will
enable any person to pull off the enamel from the ivory; and this
experiment likewise suggests the intervention of some gelatinous
membrane between the two structures. The microscope also confirms the
opinion I advance, and shows that, in the old tooth, the membrane is
absorbed, for its remains can only be detected in isolated places. I am
fully aware that none of the arguments here advanced are, with the
exception of the first, at all conclusive. Appearances are deceptive,
and results consequent upon artificial processes by no means to be
trusted. After all, however, the necessity for such a secretive membrane
is by no means imperative for the production of the enamel. Our views on
these points may be too circumscribed, since at the extremities of the
bones we see cartilage and osseous structure connected, without any such
interposition; and no one expects such a matrix for the vitreous table
of the cranial parietes. The crusta petrosa may have its uses apart from
any conjectural function of secretion; and, in further proof that it
does not secrete, it can, in the young subject, before the tooth has
emerged from its primary cavity, be separated with the greatest facility
from the enamel. It serves to protect the enamel, but it likewise
answers the end of keeping the tooth firm in the jaw: around the neck of
the molars it becomes thickened to a great extent; and at the roots,
especially of old teeth, it exhibits considerable substance. The horse's
molars are continually being wrenched from side to side while the food
is being ground, and unless they were very firmly mortised, the vessels
which nurture them would be continually lacerated: this the crusta
petrosa, by entirely filling the alveolar cavity, prevents; and as the
molars wear down with age, the thickening of the membrane enables the
jaw to retain with security the latest portion of the tooth. I have
specimens taken from very aged subjects, where the fang having been worn
away, the molar consists merely of the roots of teeth embedded in a mass
of crusta petrosa.