■IIRIIIT \ LIMARY Age of the Domestic A( BEING A COMPLETE TREATISE OX THE DENTITION OF THE HORSE, OX, SHEEP, HOG, AND DOG, AND ON THE VARIOUS OTHER MEANS OF DETERMINING THE AGE OF THESE ANIMALS. RUSH SHIPPEN HUIDEKOPER, M.D., VETERINAKIAX (ALFORT. FRANCK) : rUOKKSSOIt OF SANITARY MEDICIN.K A.M) VKTERINARY JURISPRUDENCE, AMERICAN VETERINARY COLLEGK. NKW YORK : LIEUTENANT-COLONEL AND SURGEOX-IN-CHIEF NATIONAL GUARD or PENNSYLVANIA; FELLOW OF THE COLLEGE OF PHYSICIANS, PHILADELPHIA; HONORARY FELLOW OF THE ROYAL COLLEGE OF VETERINARY SURGEONS, LONDON ; LATE DEAN OF THE VETERINARY DEPARTMENT, UNIVERSITY OF PENNSYLVANIA, ETC. ILLUSTRATED WITH 200 ENGRAVINGS. PHILADELPITIA AND LONDON : F. A. DAVIS, PUBLISHER, I89I. Agrit. Entered according to Act of Congress, in the year 1891, by RUSH S. HUIDEKOPER, In the Ofl&ce of the Librarian of Congress, at Washington, D. C, U. Philadelphia, Pa., U. S. A. The Medical Bulletin Printing House, 1231 Filbert Street. Ml bros TO THE MEMORY OF ARNIAND GOUBAUX, LATE DIKECTOR OF THE VETERINARY SCHOOL AT ALPORT, GUSTAVE BARRIER, PROFESSOR OF ANATOMY AND EXTERIOR AT THE VETERINARY SCHOOL AT ALFORT. THIS WORK IS RESPECTFULLY DEDICATED, IN RECOGNITION OF THEIK SCIENTIFIC TEACHINGS, FROM WHICH I HAVE LARGELY PROFITED AND DRAWN, AND IN SINCERE APPRECIATION OF THE MANY COURTESIES I RECEIVED FROM THEM WHEN A STUDENT AT ALFORT. THE AUTHOR 287712 PREFACE As an owner of horses and dogs, and later as a student, practitioner, and teacher of veterinary medicine, the author has constantly regretted the poverty of practical books on the domestic animals, and has felt the want of accurate text-books on many of the ordinary subjects concerning them. Upon the age of the domestic animals there exist in English but incom- plete and scattered writings ; the best of them by writers of the first half of the century, which have only been supplemented in later years by short compends, or the publication of charts of variable merit, with but a small amount of descriptive matter. The author has attempted to prepare such a book as he feels would have been of interest and service to himself in his association with animals as a layman, and would have aided his studies and appreciation of the anatomy of the teeth, dentition, and the means of determining the age. He hopes, also, that this work will furnish, to students and veterinarians, knowledge which will aid in surgical operations on the mouth. In French, German, and Italian the literature upon this subject is much more complete, and the articles in these lan- guages are much better illustrated ; so that the author lias drawn freely in quotations and translations from the list of writers found in the appended Bibliography, and has used many illus- trations where he has not believed that new drawings would be an improvement upon the older ones. He wishes to recognize (V) VI PREFACE. especially his indebtedness for many paragraphs which have been freely translated, and for a majority of the illustrations on the horse's age, from Goiibaux and Barrier ; for illustrations on the dog, from Girard ; to text and the use of illustrations on the hog, from Dr. Olof SchwartzkopfF; and the use of illustra- tions on the human mouth, from the White Dental Manufac- turing Company, of Philadelphia. Rush S. Huidekoper. Broadway, cor. Fifty-third Street, New York, October, 1891. i """"321891 Vi TABLE OF CONTENTS. Preface, . v Introduction, , . . 1 Definition of age ; periods of age. The Teeth, . . . . *? Dentition in the Horse 9 Incisors : Temporary, permanent, structure, direction. Molars : Temporary, per- manent, development and structure. Eruption of the Teeth, 43 The incisors ; tusks ; molars. Duration of the Life of the Horse 40 Principles of examination for determining the age of the horse; characteis fur- nished by the teeth. First Period. 53 Eruption of the incisors of first dentition ; at birth, one week, one month, three months, four months, five months, six months, ten months. Second Period . 64 Leveling, progressive use. and falling out of the incisois of the first dentition ; one year, sixteen months, twenty months, two years. Third Period, 74 Eruption of the permanent or adult teeth; two and a half years, rising three years, three years, three years off, rising four years, four years, four years olf, rising five years, five years, five years otf. Fourth Period 92 Leveling of the permanent incisors; at six years, at seven years, at eight years. Fifth Period 100 Wearing away of the crowns ; at nine years, at ten years, at eleven years, at twelve years, at thirteen years, at fourteen years, at fifteen years, at sixteen years, at seventeen years, after nineteen. (vii) Vlll TABLE OF CONTENTS. PAGK Irregularities OF THE Dental System, 122 Irregularities in number — augmentation ; diminution ; irregularities of form ; irregularities by uniting of two incisors ; irregularities in form of the dental cup— fissure ; irregularities in depth of the dental cups ; excess of hardness of the teeth ; excess of length of the dental cup ; fault of length or size of one jaw ; excess of width of upper incisive arch ; irregularities by excess or fault of use ; excess of length of jaws ; excess of length of incisors ; excessive length of single teeth ; deficiency of length of incisors ; deficiency of length of crown of molars ; excess of length of crown of molars ; accidental irregu- larities ; irregularities from cribbing ; artificial irregularities ; removal of temporary incisors ; bishoping ; dressed mouths. Age of the Ass, Mule, and Hinny, 157 Age of the Ox, 158 Dentition; incisors, molars; table of eruption. Determination of age by the teeth ; eruption of temporary teeth ; wearing of the temporary teeth ; eruption of permanent teeth ; leveling of permanent teeth ; wearing away of the crowns. Determination of age by the horns. Age OF the Sheep AND Goat, 175 Dentition ; incisors, molars ; eruption of temporary teeth ; alteration during the first year ; eruption of ijermanent teeth. Determination of age by the horns. Age of the Hog 184 Dentition ; incisors, tusks, molars. Determination of age by the teeth ; eruption of temporary teeth ; eruption or permanent teeth ; table of dentition. Age OF THE Dog, 194 Dentition ; incisors, tusks, molars. Determination of age by the teeth ; eruption of temporary teeth ; eruption of permanent teeth. Determination of age from other signs. Age of Man, 203 Dentition, temporary, permanent ; determination of age by the teeth. Bibliography, 211 Index, 218 Age of the Domestic Animals, INTRODUCTION. Age is defined by Webster as " the whole duration of a being," or " that part of the duration of a being which is between its beginning and any given time." It is not to be confounded with the term as appUed to the various periods or epochs of an animal's life, as the juvenile, adult, and senile, which correspond to organic metamorphosis of distinct character and to a marked cliange in tlie degree of functional activity. The age of the domesticated animals is a matter of great impor- tance in agricultural commerce, as, in the limited period during wliich each of them is individually useful, a com})aratively short time diminishes greatly the extent of usefulness to which each can be put, and consequently lowers its value as an investment. Tlie means which enable us to judge the age of an animal are based upon certain anatomical and physiological changes which occur in the course of the development of the newborn to the adult animal, and in the deterioration of it from its period of perfection to the decrepitude of its last years. These changes are constant, and, while the animal retains its general form and the tissues are chemically identical, there is a constant renewal of the molecules, which is rapid early in life and slower later. Age can be divided into tliree periods : First, juvenile, or tlie period of growth, which extends from the birth of the animal to its full development, during which it is gaining in size, in strength, and in intelligence, and is constantly increasing in its (qualities and value. Second, adult, or the stationarij period ; in this the animal is at its best ; it has every organ complete in size and perfect in function, working in perfect harmony with the rest of the body ; its intellect has the most complete control over its perfectly organized muscles, digestive tract, and other » (1) 'i AGE OF THE DOMESTIC! .\NIMALS. apparatuses, and it is capable of its best and greatest work; in this stage there is an equiUbrium estabhshed between the waste and repair, and the activity of composition is equal to that of decomposition. Third, senilitjj^ or old age, the period of deterioration ; during this period the animal may have the strength of previous years, it may be capable of as great efforts, and from experience may even display greater intelligence ; for specific purposes the animal may at this time be capable of ren- dering even, greater service than it could have given when younger, but its efforts now demand a waste of tissues no longer capable of rapid repair, and continual drains on its organs alter them in size and depreciate them in function, and the whole animal economy undergoes a steady deterioration in usefulness and value. These periods may be called that of growth, the stationary period, and that of decline. The veterinarian is the expert referee in all questions of age, and any addition to our knowledge in regard to it needs no apology. If animals lived a perfectly equable life, the changes which take place in their form and character would be regular and easy to appreciate ; but, from overwork, from the alterations produced by excessive food, want of food, or irritant substances ; from the effects of variable surroundings, at times trying on the constitution, at other times rendering the external tissues deli- cate and sensitive to exposure, the wear and tear on them is irregular. Excessive work in one animal and want of food in another open easy avenues for the ravages of time, which would not show on one which was better nourished and better cared for. The well-bred colt training over fast miles from a yearling. and the great draught-horse hauling a load of several tons in our large cities, demand excess of food for their herculean tasks. The greater quantity of food overtaxes the organs in proportion, and, in the same number of years, one animal may live double that of another in usefulness and functional activity. INTRODUCTION. ^5 We judge the age of an animal from its general aspect, from the various changes in the conformation of the body, both external and internal, and from the functional activity of its various organs. All of these are to be examined in detail, and the synthesis of the result usually gives us an accurate indica- tion of its age. The most important details in judging of the age, especially in the horse, are found in the teeth. We find the wear and tear of these organs directly in relation to the amount of aliment Avhich they have had to handle, and the amount of aliment directly in relation to the number of years which the animal has lived ; taking always into consideration that the energetic draught-horse and tlie rapid race-horse, which are obliged to do excessive work, will have their organs more rapidly modified by the excessive nature of the work Avhich they are obliged to perform. In the ox and sheep, again, the teeth are of great value in judging of age, but the epidermic products in the shape of the horns are also important factors after they have become adult. In the dog, the teeth are valuable in indicating the age of young animals, but in older ones we find that the variable mode of life to which these animals are subject so modify these organs that they are of little value, and in them we must look to altera- tion of the epidermic appendages of the skin, and to conditions in their general aspect, for our best guide. In very young animals there, is a decided disproportion be- tween the length of the legs and the size of the belly and the rest of the body, which varies with the species, the habits, and apti- tudes of the animal. In the herbivora, where the young follow their mothers to pasture and suck the udders standing, the legs are long and capable of holding the animal immediately afleo* birth ; the young see well and have the intelligence to avoid ordinary dangers from the first day. In the carnivora, on the contmry, whose search for food is often at a great distance, and so fatiguing that the young could not follow the mother, the young are born with legs too short for use and with closed eyes. 4 AGE OF THE DOMESTIC ANIMALS. which force them to remam quietly in their nests while their mothers are away, and until they have acquired considerable force and strength. In all species the young are born with a short down over the body, which serves to protect them from cold and wet ; if the animals are pigmented, this is lighter in color tlian the coat will be later. The brain and head are always large, and overhang the little faces. The digestive tract is well developed, and frequently gives the belly a swelled appearance. The tissues are soft; the bones, scarcely formed, are flexible; and while, on the one hand, they may favor deviations and de- formity, on the other they allow of considerable displacement in the helpless animal without injury to it; the liver is enor- mous, from its activity in intra-uterine life ; the lymphatic ganglia are large, as are the thymus glands and supra-renal capsules ; the ventricular portion of the heart and the arteries exceed the veins in size ; the lungs are well developed, the kidneys the same, and the nervous system is relatively ex- cessive in size, while the organs of generation may be almost ludimentary. The functions of the organs are in co-relation with their development. That of digestion is most prominent, and, in- deed, is the first and only one in the very young animal, for which it uses its inteUigence to direct voluntarily, searching and crying for food almost as soon as born, to find, at the teats of the mother, the nutrition which was interrupted at the rupture of the umbilical cord. Digestion and assimila- tion of food take place rapidly ; the circulation of the blood is frequent ; the secretion of saliva, pancreatic fluid, and bile is active, while the excretion of waste matter is small. The rapid chemical changes in the tissues of the very young is productive of a high body temperature. The function of relation is somewhat limited in the young herbivora, which, however, see, can guide themselves, and move Considemble distances ; the sense of hearing and taste is de- veloped, while that of smell is almost absent. In the young INTRODUCTION. 5 caniivora, on the contrary, the function of relation is limited at iirst to the search for and sucking of the mother's milk. As the animal gets older its parts become more harmonious. In the herbivora the body grows in all directions, the legs be- come larger without lengthening proportionately, the head elongates, the chest develops, and the belly recedes, until the young has attained the form of the adult animal. This de- velopment can be guided, hastened, and aided very materially by judicious feeding and care on the part of man. In the young carnivora the legs elongate after the other changes in development have commenced. As the animal grows the large intestine increases relatively in size, the liver and kidneys diminish, the venous system in- creases, the nervous system develops relatively much less, while the generative organs and the special senses become perfect with complete development of all the organs, and the establishment of their perfect functional activity. The points of conformation and character which distinguish the male from the female become marked, while in the very young they were scarcely appreciable. In the adult or stationary period, the animals show the distinctive characters of their species, race, family, and in- dividuality. The bodies are harmonious, the bones are solidi- fied, the organs are capable of auxiliary work, and may either be used to produce force or as store-houses of latent force, in the form of flesh, to be consumed and converted into force at a later time. At this period the sexual organs are at their best, and the sexual desire is most active. In the senile or period of decline, the rounded lines of the beautiful adult animal disappear, the bony points of the skeleton become prominent, the back drops down, the skin becomes dry and loses its elasticity, the hairs turn white, the head becomes long and pointed, the eyes sink, the muscles atrophy, the tendons contract, and the bones are subject to inflammations. The organs lessen in activity until they are 6- AGE OF THE DOMESTIC ANIMALS. unable to supply the tissues with nutritive matter equal to that which is destroyed and thrown off, and the animal emaciates. The functions slow; the senses are diminished and finally become extinct. As the determination of age, in all of the domestic animals, depends primarily on the alterations which take place in their teeth, and, secondarily, upon other signs and changes, the sub- ject will be taken up in regular order : First, the study of the dentition of the animal, the number and structure of its teeth, and the manner of eruption and the alterations which they undergo by use ; then the various other organs which undergo chamcteristic changes with age will be described, — the horns and other epidermic products, the alterations of form and of expression. The species of animal will be taken up according to its importance and value as an article of commerce. THE TEETH. The teeth are described by Cuivier as "mechanical in- struments in the vertebrated animals, at the entrance of the alimentary canal, designed to seize, cut, tear, bruise, and grind nutritive substances, before their transmission to the mouth, pharynx, and the oesophagus." Professor Owen says : " They present many varieties as to number, size, form, structure, position, and mode of attachment, but are principally adapted for seizing, tearing, dividing, pound- ing, and grinding the food. In some species they are modified to serve as formidable weapons of offense and defense ; in others as aids in locomotion, means of anchorage, instruments for uprooting or cutting down trees, or for transport and working of building materials." Chauveau says : " Identical in all of our domesticated animals, by their general disposition, their mode of development, and their structure, in their external conformation these organs present notable differences the study of which offers the greatest interest to the naturalist, for it is on the form of its teeth that an animal depends for its alimentation. It is. the regime^ in its turn, which dominates the instincts and commands the diverse modifications in the apparatus of the economy ; and there re- sults from this law of harmony so striking a correlation between the arrangement of the teeth and the conformation of the other organs, that an anatomist may truly say : " Give me the tooth of an animal, and I will tell you its habits and its structure." All of the domestic animals have two sets of teeth : first, those o^ first dentliion^ which appear at or soon after birth, which are known as foetal^ temporary^ miJlc^ deciduous^ or caducous teeth ; second, those of the second dentition^ which are known as replacing^ persistent^ or permanent teeth. 8 AGE OF THE DOMESTIC ANIMALS. The teeth of both dentitions are placed in each jaw so as to form more or less of an arch, or horseshoe, the convex por- tion forward and the open end facing toward the posterior part of the mouth and throat. These arches are subdivided into three portions, an anterior, a lateral, and an intermediate, and in each section the teetli have characters which distinguish them from the others, and distinctive forms which indicate the use to which they are adapted. In the anterior arch the teeth are sharp-edged, and are adapted for cutting or nipping the food ; these are called incisors {incidere, to cut), and are most characteristic in the herbivora. In the intermediate section the teeth are large, pointed, and sharp, destined to tear the food or to serve as weapons of offense and defense; these are called tuslcs^ tushes^ fangs ^ or canine teeth ; they are most developed in the carnivora, which tear their food. The lateral arches have broad, strong teeth, with flat sur- faces, admirably fashioned for the grinding of the food, from which they take the name of molars {molere, to grind), or grinders. These are sometimes subdivided into premolars and f>ost-molars, or molars proper. As the teeth on the two sides are symmetrical, for conveni- ence of description zoologists have adopted the following formula to indicate the number of teeth in either dentition or at any given period of an animal's life ; it gives only the teeth on one side of the mouth : — T z= incisors, T = tusks, M = molars. Thus, for the permanent dentition of the horse : — Superior jaw | i 3 ^ 1 ^ ^ 6^ _ 20 ; both sides, 40. Inferior jaw ) 3 l 6 Or, more simply : — 3.1.6 == 40. DENTITION IN THE HORSE. pen.ponu-y, .... ^-^^^^ = 24 Formula J I ^ 1 r I Permjuient, „ ' ' ^ = 40 The horse has thirty-six or forty teeth, according to the sex of the animal, which are divided into three groups, — the incisors^ the molars, and the tusks. In front are the incisors, to each side the tush or canine teeth, and still farther hack, on the sides, the molars. (Fig. 1.) The first are used to grasp and cut the food, the second to tear it, and the third to hruise and grind it up. Following their position in the jaw, the teeth form a paraholic curve, known as the dental arches, of which there are two, — one in the upper jaw and one in the lower jaw. These arches are again subdivided into three portions, an anterior and two lateral. The incisor teeth form the anterior part, in the shape of a half- circle, convQX in front. On each side, directly behind the in- cisors is a space, larger or smaller, according to the sex of the animal, which corresponds to the intermaxillary and maxillary bones, and extends to the lateral part of the dental arch. This is known as the interdental space. It is plain and extensive in mares, because they ordinarily do not have tush teeth ; but when they do, as in the male, it is divided into two parts, known as the anterior and posterior. The latter, in the lower jaw, is known as the bar of the jaw. Further behind, to the riglit and left, forming, as it were, branches or sides to the dental arch, are found the molar teeth. In the adult animal there are in each jaw six incisors, two tush teeth, and twelve molars, making a total of forty for the horse, and, without the tush teeth, thirty-six for the mare. In the colt there are twelve incisors and twelve molars, the latter divided into rows of three above and three below on each side. In the young animal the tush teeth do not exist. How- (9) AGE OF THE DOMESTIC ANIMALS T' Fig. 1. Complete dentition of the horse. P, pinoher teeth ; I, intcnncdiatt" tt-cth ; C, corner teeth ; T, tush or canine teeth ; S M, supplementary proTuohirs ; DM, deciduous molars ; M P, permanent molars. INCISORS. 11 -ever, in the place where they will appear later, we sometimes find small, rudimentary teeth with no defined shape. We again sometimes find, both in the young and in the adult animal, a more or less rudimentary premolar tooth, commonly known as the wolf tooth, which raises the number in the adult animal to forty-four. INCISORS. INCISORS OF FIRST DENTITION. The milk-teeth, known also as deciduous or foetal teeth, are twelve in number, — six in each jaw, three on each side. The Fig. 2. A milk-tooth. A, posterior face ; B, anterior face ; C, profile. middle ones are known as pincher teeth, the next as the inter- mediate teeth, and the outside ones as the corner teeth. They are at first imbedded in the body of the bone, and cohered by the gum ; but when they have protruded from the alveolar cavities they form a half-circle, convex in front. Compared with the permanent teeth, they are shorter ; they have a con- striction in the centre which is known as the neck, which divides them into a free portion or crown, and an imbedded por- tion or root (Fig. 2). They are dead white, milky, or yellowish white in color. The anterior face of these teeth is convex in both directions and roughened by little parallel, longitudinal ridges and depressions, which, however, become worn off, and 12 AGE OF THE DOMESTIC ANIMALS. have a smooth and poUshed surface as the animal becomes older. The posterior face is concave from above to below, and slightly convex from side to side. The internal border of each tooth is thicker than the external. In a virgin tooth (Fig. 3), or one which is not worn by use, the free portion of crown is divided from in front to behmd and limited by two borders, one anterior,, a, and the other posterior, h, which are separated by a cavity known as the cup, c. The anterior border is the highest and longest ; it is shaped convex transversely, and is the first portion of the tooth to come through the gum. The posterior border is "be a Fig. 3. Longitudinal section of a virgin milk-tooth in its alveolar cavity. shorter and appears later, but soon reaches, however, the level of the anterior border from the wearing down of the latter. From the same cause the cavity or cup, which first existed, gradually disappears. This is known as the leveling of the teeth. The imbedded portion or root also contains a cavity, known as the internal dental cavity, or pulp-cavity (c/), which protects the papilla or pulp of the tooth ; but as the animal be- comes older the tooth elongates by the growth of its imbedded portion, and the internal cavity diminishes in calibre and is nearly obliterated by a deposit of bony substance ; at the same INCISORS OF FIRST DENTITION. 13 7catf' Pig. 4, b. Temporary incisors, front face, a, upper jaw ; b, lower jaw. The roots are uncovered to show their position in the alveolar cavities. u AGE OF THE DOMESTIC ANIMALS. Fig. 5. Temporary incisors, profile anil table. In profile the roots are uncovered to show their position in their alveolar cavities. INCISORS OF FIRST DENTITION, 15 time the bone of the jaw mcreases in size, and the permanent incisors form in them. These develop behind the deciduous teeth, and are at first separated from them by a bony septum, which, however, usually becomes thinned, and the permanent tooth pushes the other out. Fig. 6. A, permanent incisor just before eruption ; B, deciduous incisor in place. but sometimes they come from an independent opening and the milk-tooth remains in place. The absorption of the bone, by pressure of the developing teeth, is frequently attended by constitutional phenomena, loss of appetite, sluggishness, etc., and I have seen it produce convul- sions in a colt two and a half years old. There is an old superstition that the period of eruption of 16 AGE OF THE DOMESTIC ANIMALS. the permanent incisors predisposes the animal to the contraction of contagious fevers. PERMANENT INCISORS. The permanent incisors are six in number in each jaw, like the deciduous incisors which they replace ; they, like the latter, are known as the pincher teeth, intermediate teeth, and corner teeth. They are longer than the milk-teetli, are more of a wedge- shape, have no constriction or neck separating tlie crown from the root, and are of a bluish-white, instead of the cream color of the others. The permanent incisors (Fig. 7) are shaped somewhat Fig. 7. A Tirgin inferior permanent incisor. A, anterior face ; B, posterior face ; C, profile. like an irregular cone, of which the base corresponds to the crown or free extremity, and the summit to the root or the imbedded extremity. They are curved on their long axis, with their con- vex face in front and their concave face behind, and they are also somewhat twisted on their long axis; the pincher teeth are slightly so, the intermediate teeth more so, and the corner teeth sometimes make almost a decided S. The free portion, or crown, is flattened from in front to behind, at the level of the gums the two axes have about the same diameter, and the root or imbedded portion is flattened from side to side. PERMANENT INCISORS. 17 The anterior laee, which is widest above, is fiat troiii side to side and convex from above to below. It frequently is grooved by a little canal, which is most distinct on the free por- tion of the tootli. The incisors of the upper jaw are more con- vex than those of the lower jaw, and they frequently have two little longitudinal canals instead of one. The posterior face is convex and rounded from side to side and concave from abov(^ to below. Tlie internal border of the tooth is thicker than the external ; this is more marked in the imbedded portion than in Fig. 8. - I. Longitudinal section of a permanent incisor, leveled. II. Eccentric and longitudinal sei^tion of superior and inferior intermediate permanent incisor, to show the ditferential characters of the dental cixp. the free portion. The free portion, or crown, is flattened from in front to beliind, and is hollowed out by a cavity known as the external dental cavity or cup. (Fig. 7, B and C.) In the virgin tooth there is a border in front and a border behind ; the latter is not so high as the first, but in old teeth these become worn off until perfectly level, when the extremity of the tooth takes the name of the table of the tooth. (Fig. 8, I, upper extremity.) The external dental cavity (Fig. 9, <( n a), surrounded by 18 AGE OF THE DOMESTIC ANIMALS. I P Fig. 9. Longitudinal and antero-posteiior sections of permanent incisors. P, pinchers ; I, intermediate ; C, corner ; a a a, free e.vtremities ; b b b, roots. the cup of enamel, has an irregular, conical form, the base toward the free extremity of the tooth itself and the point im- bedded in the tooth toward its root, but inclined slightly toward the posterior border, especially in the inferior tooth. PERMANENT INCISORS. 19 This is sometimes a hollow cup, but it is frequently filled %vith cement, making the free extremity, even in the virgin tooth, in such cases perfectly solid. The cups in the inferior teeth are less deep than those in the superior incisors. In the incisors of the lower jaw the pincher teeth have a. cup with an average depth of 16 to 18 mm. ; the cup of inter- mediate teeth is 18 to 20 mm., and that of the corner teeth is 11 mm. to 13 mm. In the upper jaw the cup of the pinchers is 25 mm. to 27 mm. deep; that of the intermediate teeth, 27 mm. to 28 mm. deep; and that of tlie corner teeth somewhat less, 18 mm. to 20 mm. (Fig. 9, a a a ; Fig. 12, c.) The cups m the lower teeth incline nearer the posterior border of the tooth than in the upper ones. In the imbedded portion of the tooth there is a large canal which holds the dental pulp or papilla, which is known as the internal dental cavity. (Fig. 9, h ; Fig. 12, P.) Examine Fig. 9, and we find that this cavity occupies the centre of the tooth, in the root, but toward the crown inclines toward the anterior face and penetrates between the latter and the cup of enamel. As tlie tooth becomes older this cavity becomes filled with an ivory- like substance, softer and darker colored than tlie rest of the tooth, and when it appears on the table of the tooth, from the wearing away of the crown, it is known as the '•^dental star.^^ In order to understand clearly the various forms which the table of the tooth assumes as it wears away, a series of sections are shown in Fig. 10, representing the table as it appears from the use of successive years. A. The rubbing surface of the dental table is at first flat- tened from in front to behind ; that is to say, its trans^ erse diameter is greater than tlie antero-posterior. (Sections 1 and 2.) B. It becomes oval ; there is still a disproportion between the extent of its two diameters, but the transverse diameter remains greater than the antero-posterior. (Sections 3, 4, and 5.) (7. It becomes rounded and its two diameters are nearly equal. (Sections 6 and 7.) 20 AGE OF THE DOMESTIC ANIMALS. 1 B Fig. 10. Series of transvorso sections of tlie ri^lit-liaiid inferior permanent incisors of a five-year-old horse. A. forms tiatt('n('), depressed from in front to behind, fills the cavity which hollows out the root of the tooth. The surface of the first is destined to the formation of the enamel of the tooth, which function it completes by the time the tooth has appeared through the gum, when the papilla disappears. 22 AGE OF THE DOMESTIC ANIMALS. The other, which forms the ivory or dentine, remains until a more or less advanced period of the life of tlie animal, and furnishes the tooth witli its vitality. In the interspace between these two papillary systems is deposited the matter which constitutes the bulk of the tootli (Fig. 11, d). This at first consists of a very thin, conical plate hollowed out on the inside, and containhig a deep depression on its free extremity. Later, the walls of the dental fol- licle (Fig. 11, c) are trans- formed into the alveolar periosteum. If we refer now from Fig. 11, where we find a, the papilla of the enamel; h, the papilla of the ivory ; d, the plate consisting of the deposits of these two papillae, — that is, the enamel and dentine juxtaposited, — and c, the germ sac, which is to become the alveolar perios- teum, to Fig. 12, which is a longitudinal antero-posterior section of an inferior perma- nent pincher tooth, fully developed (somewhat en- larged), we find E, the enamel of the cup, surround- ing this cavity, from which the papilla has entirely disappeared ; P, the cavity of the ivory papilla very much diminished in size ; 7, the dentine occupying the major portion of the tooth, having developed on the inner surflice of the thin plate which we found in Fig. 11. In Fig. 12, at T, which represents the table of the tooth after the borders have been worn, we find a separation of the enamel of the cup and the ivory enamel (Fig. 12, E E)^ which we find continuous in Fig. 11, dd. Fig. 11. Schematic section of the dental follicle of an inferior incisor in the horse, a, sui)erior papilla, — germ of the enamel ; b, inferior papilla, — dental pulp or germ of the ivory ; c, wall of the follicle; d, plate of enamel and dentine juxtaposited. STRUCTURE OF THE INCISORS. 23 Three substances enter into the structure of the teeth, — one fundamental, the dentine or the ivory, and two covering sub- stances, which differ from each other very much, and are known as the cement and the enamel. 1. The Cement (Fig. 12, G O'— The cement forms the most superficial layer; it is deposited di- rectly upon the enamel over the whole surface of the tooth, and dips into the cup, which it fills more or less completely in different subjects. Sometimes it is excessively thin, 2 to 3 mm. ; at otlier times it is from 10 to 15 or even 20 mm. in thickness. It is generally tliicker in the lower teeth than in the superior. MM. Chauveau and Arloing, in France, and Mr. Mayhew, in Eng- land, were the first to call attention to the importance of this in judging age. It will be readily seen that the size of the cavity in the dental cup depends greatly upon the amount of the cement which is deposited in it. It is Fia. 12. Longitudinal and antero-posterior section of i»er- manent incisor (enlarged). F A, anterior, F P. pos- terior face: C, cement: E, enamel ; I, ivory, or den- tine : T c, external dental cavityj or cup of enamel lined with cement ; P, internal dental or pulp cavity. 24 AGE OF THE DOMESTIC ANIMALS. exceedingly rare to find excess of depth due to increased deptli of the enamel, which condition will, however, be considered in the study of the abnormalities of the teeth. The cement is a protecting layer which offers only a mod- erate resistance to the friction of food and other substances, and disappears at an early date from tlie periphery of the tooth, while t'ementation of thi' roots Fig. 13. • f thrt incisors. A, dental tables alveolar cavities. B, roots in theii it persists in the cup of the tooth so long as the latter remains on the table, where it forms a whitish spot, surrounded by a band of enamel. (Fig. 10, A^ B, and C.) The cement is shown by microscopical examination to be a bony formation, secreted by the alveolar periosteum (germ sack), and is not a transformed ivory or dentine as given by Simonds. It is found in greatest quantity at the crown or free STRUCTURE OF THE INCISORS. 25 extremity of the tooth ; but in very old horses, when the teeth have worn down to the roots, and the dentine, no longer pro- tected by the enamel, offers a diminished resistance to the fric- tion to which they are exposed, the irritation of the dormant periosteum sets up a new secretion, and cement is thrown out often in very great quantities to strengthen weak roots. As the inferior incisors are the shortest, and the first to wear away, we more frequently find the large masses of cement in the lower jaw. We again find excessive deposits of cement around the roots of the teeth when they have been loosened or irritated in their cavities by the rough pressure of bits, or have been injured by any accidental cause. Tins occurs most frequently in vicious or playful horses which have the habit of biting roughly at foreign bodies. We see in this a wise provision of nature to succor these important organs after accident, and from the effects of old age. 2. The Enamel (Fig. 12, EE ; Fig. 11, outer surface of d). — The enamel is the true protecting layer of the teeth. Under- neath the cement it forms a sort of armor which covers the sur- face of the dentine and forms the walls of the cup. It does not reach the cavity of the pulp. It is thicker, and covers a greater extent on tlie anterior face of the tooth than it does on the pos- terior. (Fig. 12, E E.) This furnishes an important factor in determining the age of very old horses, when tlie tooth either becomes triangular or biangular. In the wall of the cup the enamel has about the same thickness throughout, although the difference of a transverse or an oblique section may give a deceptive appearance of a greater thickness at one point than at another The enamel has a wonderful hardness. While still inclosed in the germinal sack it is readily cut by a knife and its elements can be dissected into Z-shaped prisms. From the moment that it is exposed to the air it becomes so hard that it will strike fire from flint. As it is more resisting than the dentine, it constantly stands in relief on the surface of the table of the tooth. 26 AGE OF THE DOMESTIC ANIMALS. Histology. — The enamel is of epithelial origin, formed from the superior papilla of the primitive folUcle. On microscopical examination it is found to he composed of an infinity of little hexagonal prisms, intimately joined and directed ohliquely to the suhjacent surface. The deepest layers lie immediately over the peripheral lacunae of the dentine. 3. The Fundamental Substance, Dentine, Eburnated Substance, or the Ivory (Fig. 12, /). — This constitutes the niajor part of the tooth. It is produced by the inferior papilla or pulp, has a deep depression in its free extremity for the dental cup, and is covered by the enamel. It forms the walls of the pulp-cavity. In the forming tooth, the dentine consists of a thin layer juxtaposited to the layer of enamel formed by the superior papilla (Fig. 11, d); but as the tooth develops, successive layers are deposited on the interior of the first, and the ivory gradually encroaches upon and diminishes the size of the papilla lodged in the pulp-cavity until the latter entirely disappears. The deeper layers have a darker color than the first, as in their continual infringement on the vascular papilla they im- prison a portion of its organic matter and blood-supply until they have produced a complete atrophy of their progenitor. This discoloration of the dentine we shall find later, on the table of the tooth, under the name of the " dental star," which becomes an important factor in judging of age after eight years. Strictly speaking, there are two stars, but the posterior is very rudimentary and of no practical importance. It is occasionally^ however, seen very distinctly. In Fig. 14 we have a series of longitudinal antero-posterior sections of incisor teeth from horses of different ages, which show the gradual diminution of the pulp-cavity from the en- croachment of the dentine. The dentine toward the root of the tooth is always of a darker color than that toward the crown. The ivory is less hard than the cement, but much more resisting than either the cement or the bone in which the tooth is imbedded. Histology. — The dentine is clianneled by a multitude of canalicuU, which radiate from the pulp and after frequent anas- STRUCTURE OF THE INCISORS. 2T 2 3 a ^ 3 o ? ^1 p d 3^ i* g r^^ re S a 2 3 J 3. => S 3 tomoses terminate in laciinse under the deep layer of the enamel {interlobular spaces of Czermak). The Table of the Incisors. — The table of the incisors is 28 AGE OF THE DOMESTIC ANIMALS. the free portion or crown of these teeth, which becomes worn by friction with the liard substances which the animal takes as food, and by the constant contact with the teeth of tlie opposite jaw. After the high anterior and lower posterior borders of the virgin incisors have been worn away the table is established. At first this consists, on each tooth, of an oblong plate, wider from side to side, which is surrounded by the layer of cement directly covering the peripheral layer of enamel ; inside of this is found tlie zone of yellowish and softer dentine, usually somewhat de- pressed on account of its lesser resistance to friction ; in the Transverse section of an incisor tooth. Inferior, riglit side. A, anterior; B, posterior ; E, periplieral enamel ; E', cential enamel ; C, peripheral cement ; C', central cement ; I, ivory, or dentine. (Enlarged.) middle, the central enamel or border of the cup surrounds the variable quantity of cement which may be deposited in it. (Fig. 10; Fig. 1*2, ^; Fig. 15.) As the table gradually encroaclies upon the wedge-shaped tooth (Fig. 16), it becomes proportionately narrower in its trans- verse diameter, and as it becomes oval in shape the cup is found nearer the posterior border of tlie tooth instead of in the centre. The dental star, or dark-colored dentine which takes the place of the papilla, now appears between the cup and the anterior border of the tooth (Fig. 12, P; Fig. 10, B.). A still further DIRECTION OF THE INCISORS. 29 destruction from use brings the table to the middle of the original tooth ; when it assumes the round form, the cup of central enamel has disappeared, and the dental star is now mid- way between the anterior and posterior borders. (Fig. 10, (7.) Still further use brings the triangular form, and finally the biangular; in these two. forms the dental star gradually becomes larger, and, at times, when the papilla has not been entirely replaced by the dentine, a cavity is found which, by tlie un- informed, has been mistaken for the cup (Fig. 10, (7 and 7>), but should not be, as there is no surrounding enamel. Figure 16 shows the forms at the various parts of the original tooth. The Direction of the Incisors. — The direction of the incisors, or the posi- tion which they hold in regard to the jaw, is to be studied first in profile, considering the relative angle which the incisors of the upper and lower jaws have to each other ; and second, in face, considering the position which they hold in regard to the median line. Direction of the Plane of Con- tact OF the Two Jaws (Fig. 17). — In a young horse the incisors meet and form an arch which, if viewed in profile, rep- resents tlie half of a circle; so that a tangent drawn from the point of contact of the two jaws is perpendicular to their tables. But as the progressive wearing of the table brings it nearer to tlie roots of the teeth, the half-circle changes to the form of an ogive, which becomes more and more acute as the surface of contact, which is displaced above and below parallel to itself, extends gradually from the primitive diameter. Consequently the tangents, a a\ b h\ c c', drawn from the new points (a, &, c) of contact of the arches, are no longer perpen- dicular to this point, but tend to become parallel. As the angle of incidence of the incisors increases in Fig. 16. Scheme of sections of wedge- shaped incisor. so AGE OF THE DOMESTIC ANIMALS. obliquity with age, and the horizontahty of their arches in- dicates approximately the degree of the alteration, — excepting, of course, certain abnormal changes to be studied later, — we have in the profile of tlie jaw a valuable factor by which to judge of the age of the horse. Direction in Regard to the Median Line (Fig. 18). — In the vouns: horse, the crowns of the six incisor teeth widened from side to side, while their roots are flattened in their trans- FlG. 17. Arch of the incisors, uncovered to show tlieir successive planes of contact. verse diameter, cause the teeth to take a position on the end of the jaw like the ribs of an open fan. They diverge from the alveo- lar cavities, in which they are imbedded in the bone, toward the circumference formed by their crowns. But, as age advances, the crowns become worn ofl*, and the teeth are pushed farther and farther out of their cavities. The roots, which were at first almost in contact with each other, gradually separate and widen, while the circumference constantly diminishes as the teeth THE. TUSHES, TUSKS, CANINE TEETH. 31 become worn down, until they assume a parallel position, and finally converge, instead of diyerging, at their free extremities. The intermediate teeth become separated from the pinchers on the one side, and the corner teeth become separated from them on the other, until a distinct space is yisible between them, which is filled by a pale gum. En resume in regard to the general direction of the incisors : — 1. The . incidence of the arches acquires a greater obliquity with age. 2. Their incurvation and their transverse diameter di- minish. 3. The teeth, at first di- verging from their roots, become parallel and finally converge toward their free extremities. THE TUSHES, TUSKS, CANINE TEETH. The tushes are four in num- ber in the adult horse ; they are rudimentary or absent in the mare. In certain sections of the country superstition has attributed sterility to mares provided with them, which is, however, abso- lutely unfounded. The superior tusks are placed one on each side of the upper in- terdental spaces, at the point of union of the superior maxillary and intermaxillary bones. The lower ones are placed on either side of the maxilla, always closer to the incisor teeth than those of the upper jaw, so that they are invariably in front of the latter. The canine teeth are curved in their long axis with the Fig. 18. Incisors of the two jaws (roots un- covered), seen by their anterior face to show their direction in regard to the median line. 32 AGE OF THE DOMESTIC ANIMALS. concavity backward, and they project slightly outward. The external face is covered with small, longitudinal, parallel stria- tions. The internal face has a conical eminence pointing toward the free extremity of the tooth and separated from its borders by deep gutters. The tusks have a pulp-cavity relatively much larger than that of the incisors, which, however, also becomes filled with a discolored dentine as the tooth advances in age. As the tusks become used they show in their centre a dental star, which sometimes is very dark in color. While the tusks A B Fig. 19. Upper right-hand canine tooth of a horse. A, external face ; B, internal face. Fig. 20. Longitudinal antero-posterior section of a horse's canine tooth. C S, superior canine : C I, inferior canine. may be subject to much use from the friction of food, the tongue, lips, and the bit, they are always prominent, even in very old horses. Goubaux and Barrier have seen one case in which the tusks of the upper and lower jaw were in contact. Structure. — The tusks are composed of ivory or dentine, inclosing a pulp-cavity and surrounded with enamel. There are no temporary tusks in the horse, although small, rudimentary spicula sometimes are found before the permanent teeth appear. MOLARS. PREMOLARS WOLF-TEETH. These teeth, which were first described by Daubenton, are. not found in all horses. They occur much more frequently in', the upper jaw than in the lower one, and are rarely found in botli in tlie same animal. Girard says that they usually appear about tlic tenth month, and drop out at the time of the eruption of the permanent molars. The alveolae are usually directly hi front of those of the first molars. They are, however, frequently a half-inch or more in front of the others, and often remain until the animal has reached an advanced age. Their presence ren- ders the dental formula slightly variable (forty-four for the horse and forty for the mare). The wolf-teeth are elongated and slightly curved on their long axis ; they resemble a good deal tlie incisive teeth of the carnivora, from which, perhaps, comes their common name. Their roots are unicuspid. Girard de- scribes supplementary post-molars, which, however, are not recorded by other authors, and were probably anomalous teeth. MOLARS. The molars fill in the sides of the dental arch ; like the incisors, they appear in two groups, — the temporary and per- manent teeth. MOLARS OF FIRST DENTITION. The (Jedditoits, temporary^ milk, or molars of first dentition^ are twelve in number, — six in each jaw, three on each side. By some curious error, the father of veterinary anatomy, Carlo Ruini, 1598, and his immediate followers, considered that there were but eight temporary molars. These teeth are strong, short, and have the general form of quadrangular prisms, except the first in each row, which is triangular. The anterior and posterior faces are smooth ; in the upper jaw the first tooth has three longitudinal canals on its external 3 (33) u AGE OF THE DOMESTIC ANIMALS. face, while the second and third teeth have two ; the internal faces are irregular, slightly concave in their long axis, and show canals very much less marked than those on the outside. The inferior teeth on their external face have a single gutter, which is deepest in the first tooth and most shallow in the last ; on their internal face they are irregularly grooved. All of the milk-molars have a constriction or neck separating their crowns F I * s F E Mm |.f f ImM. Fig. 21. The three superior temporary mohirs (right). F I, internal faoe ; F E, external face. from their roots. They have each two roots, one anterior and one posterior. These are strong, convex outside and concave inside ; each is hollowed by an opening which reaches into the tooth itself Just before being forced out by the permanent teeth the roots are sometimes divided into little eminences by the pressure of the irregularities on the crowns of the latter. The free extremities of the virgin milk-molars are irregular and MOLARS OF SECOND DENTITION PERMANENT MOLAKS. 85 covered with ridges and cavities, but the external border ol' the superior teeth and the internal border of the inferior teetli arc always longer than the opposite border, so that they present two oblique planes, which become more marked as the teeth wear down. As the animal becomes older the molars wear down till they are reduced (Figs. 23 and 24) to little thin plates, Fig. 22. The three inferior temporary molars (right side). F 1. internal face : 1" K, external face. which fit close to, or cap, as it were, the crowns of the replacing molars, by which they are finally forced out from the jaw. MOLARS OF SECOND DENTITION PERMANENT MOLARS. These are twenty-four in number, — twelve in each jaw, six on each side. They are designated numerically from in front to behind, as the first, second, etc. The tlinv first, whicli S6 AGE OF THE DOMESTIC ANIMALS. replace the temporary molars, are known as pre-iiwlars^ and the last three as the post'inolars. Each row of six molars forms a branch of the dental arch, which in the upper jaw is slightly convex to the outer side, while in the lower jaw it is perfectly straight, with the anterior extremities inclined toward the other, so that they form a sort of V, and are overlapped by those of the upper jaw. A Fig. 28. A, transverse seotion of the lower jaw. showing the third temporary molar and its rehition to the permanent molar which replaces it. B, third inferior i>pr- manent molar, capped by the worn temporary molar. The permanent molars have the shape of quadrangular prisms flattened from side to side, except the first and sixth, which are triangular. Superior Molars. — The posterior faces are almost smooth, except in the sixth molar, where the face is replaced by a blunt edge ; the anterior faces are also smooth, except that of the first molar, which is replaced by a sharp border. MOLARS OF SECOND DENTITION PERMANENT MOLARS. 37 The external faces have two longitudinal gutters separated by a ridge; the first molar has three gutters with two ridges; the internal faces have two shallow gutters on the first molar and one on each of the others, which is closer to the posterior border of the teeth in the last ones. There is no neck or dis- Fig. '24. A, transverse section of the upper jaw, showing the left third temporary molar and its relation to the permanent molar which replaces it. B, third perma- nent molar, capped by the worn temporary molar. tinctive line (Fig. 24) separating the crown or free extremity from the roots or imbedded extremity of the permanent molars. The free extremity is triangular in the first and sixth teeth, and quadrangular in the others. In the virgin tooth it has an ir- regular surface resembling an Old English ^. with loops looking 38 AGE OF THE DOMESTIC ANIMALS. -^X }M Fig. 25. Kight-hand superior molars of a horse 0 t* 7 years old. ?^ir8t molar at top of figure. Fig. 26. Left-hand inferior molars of :i liui.^e i) to 7 years old. First molar at top of tij^ure. MOLARS OF SECOND DENTITION PERMANENT MOLARS. 39 toward the inside and surrounding cavities, which are more or less filled with cement ; to the anterior loop is attached a small, secondary loop. The external border is always longer than the internal. As the tooth wears and the table is estab- lished, the cavities disappear. At first the imbedded portion is hollowed by cavities, which reach the body of the tooth itself and contain the papilla, or pulp, formed principally of blood- vessels and nerves; later, these resolve into distinct roots, three each for the first and sixth molars, and four each for the otliers. According to Girard, these become distinct at five years of age. Fig. 27. Superior permanent molar (right side),— virgin tooth. E, external face ; I, internal face ; E I, surface of contact. (Fig 27.) If the head is placed horizontally the first molar is found imbedded in a vertical position, while the others incline somewhat from below to above and from in front to behind. The superior molars are implanted in alveolar cavities, pris- matic like the teeth, and separated from each other by bony septa, whicli are thin at their free borders and thicker above. The bottoms of the three last project into the maxillary sinuses, while those of the three first are in the superior maxillary bone itself In very old liorses the sinus may reach the root of the third or even second tooth. 40 AGE OF THE DOMESTIC ANIMALS. Inferior Molars. — The anterior and posterior faces are flat, except the posterior of the sixth tooth and the anterior of the first tooth, which are replaced by sharp edges. The ex- ternal faces have one longitudinal gutter hi the first five teeth and two in the sixth tooth. The internal faces have three gutters in the first and sixth teeth and a variable number in the others. The free extremity is triangular in the first and sixth molars and quadrilateral in the others ; but these are narrower from side to side than from in front to behind. They are longer on their internal border than on the external, and have the Old English ^ turned with the loops outward. The imbedded por- tion is bicuspid in the first five teeth and unicuspid in the sixth. The divisions of the roots diverge ; each contains a cavity for the pulp. development and structure of the molars. In the superior molars the papilla of the enamel in the B A Fig. 28. A right superior molar taken from the dental follicle. A, view from free end; B, view from the imbedded portion; a, anterior infnndibnla ; a', posterior infundibala; e, external border of the infundibula ; i, internal border of the in- f undibula ; c, accessory column of the anterior infundibula. germinal sack is double and penetrates into the tooth, forming, practically, two infundibula, one anterior and one posterior, in- stead of one cup, as in the incisor teeth. The papilla of the pulp makes five diverticula, which almost appear to be as many separate cavities. In the inferior molars there are two infundibula, one occu- pying the middle portion of the tooth and one toward the an- terior portion, which allows us to recognize a left-hand inferior The arrangement of the molar from its riglit-hand homologue. DEVELOPMENT AND STRUCTURE OF THE MOLARS. 41 infundibula of the papillae of the root is practically the same as in the superior molars. The molars, like the incisors, are composed of a funda- mental substance and two covering layers. Grinding table of a superior molar (left). Fig. 29. Table of an inferior molar (right). A. The Enamel forms the bulk of the tooth. It covers the four faces and is reflected into the infundibula. On the table Fig. 30. Transverse section of superior molar (left). Enlarged. of a molar which has been worn down it forms the bright lines which form the Old English §. B. The Ivory or Dentine is deposited on the internal face of the enamel, and finally fills up the diverticula of the pulp- 42 AGE OF THE DOMESTIC ANIMALS. cavity. At first it is entirely protected by the enamel, but as the table is formed it becomes exposed, and, as it is softer than the other substance, becomes worn more rapidly, and renders the wearing surface uneven and better adapted to grinding. Fig. 31. Transverse section of an inferior molar (right). Enlarged. C. The Cement is very abundant on the molars. It covers the enamel, fills the infundibula of the enamel, and, in very old mouths, is often formed in excess, and furnishes a new wearing surface to replace the teeth themselves, wliich have been destroyed by use. ERUPTION OF THE TEETH. ERUPTION OF THE INCISORS. The eruption of the deciduous incisors does not cause any marked constitutional phenomena, although it may cause some slight loss of appetite, — due, however, rather to the local pain in chewing than to any general disturbance. With the appearance of the permanent teeth the head increases in size and becomes more full, which is due principally to the space demanded for the large molars of second dentition. The appearance of the permanent teeth is a period of general irritation of the animal economy. The first attack of periodic ophthalmia frequently appears at this time ; colts seem more susceptible to contract strangles and other of the contagious diseases. Sometimes the temporary incisors drop out before the ap- pearance of the permanent teeth ; in this case they leave a small ulcer in the gum, which is followed by a swollen, red, sore point, through which finally the replacing tooth appears by its internal corner, which is followed by the anterior border, set not in its future proper position, but obUquely to the axis of the jaw. When the temporary teeth have been pulled to hasten the age, as is a growing custom in some of our neighboring- markets, the obliquity remains, and when found in an apparent iive- or six-year-old mouth should always be regarded with sus- picion. At other times the milk-teeth remain, and the permanent ones protrude on their posterior border. Convulsions may occur by excessive pressure and irritation in these cases. The incisors of the upper jaw usually appear before those of the maxilla. The pincher, intermediate, and corner teeth appear in succession by pairs. Causes loJiich can Hasten or Retard the Eruption of the Incisors of the Secwul Dentition. — All ordinarv horses are ■ (43) 44 AGE OF THE DOMESTIC ANIMALS. supposed to be born on the 1st of May, while thoroughbreds are supposed to be born on January 1st, and each dates its age accordingly. We may, therefore, have horses which officially have the same age vary from each other in their real age by some months. Races which develop slowly, a debilitated temperament, and an impoverished nourishment, all tend to retard the eruption of the teeth, while, on the contrary, precocious races, strong feeding, etc., hasten the appearance of the full mouth. Gestation in the young mare retards the eruption of her teeth, especially of the corner teeth, which mark the five years. In cold, damp climates the teeth are several months later in appearing than they are in warmer and dryer climates. The thoroughbred and all improved horses develop their full mouths earlier than their less well-bred relations. Exceptions may occur in both extremes. A rising three-year-old has been known to have all of its per- manent incisors, and more frequently a six- or seven-year-old is seen with its corner milk-teeth. ERUPTION OF THE TUSKS. The appearance of the tusks is so variable that it is of little value as an indication of age. They are usually absent in the mare, and in the horse or gelding may be out at three years, or may not pierce the gums until the animal has had all of its other permanent teeth. The lower tusks frequently appear almost a year in advance of the upper ones. They usually appear at about the same time as the corner incisors. ERUPTION OF THE MOLARS. As the young horse becomes older the deciduous molars become worn down until they only exist as thin plates which cap the crowns of the first three molars of permanent dentition and are but loosely held in their alveola. They become broken, and the sharp points wound the neighboring cheek, causing difficulty of mastication, which can frequently be relieved by removal of the loosened teeth. The two first molars of first dentition are through the ERUPTION OF THE MOLARS. 45 gums at birth, or within a few days of it. The third appears at the end of the first month. The authorities are not in accord as to the appearance of the permanent molars, as will be seen in the following table: — Designa- tion OF Epoch of Eruption. Designation of Tooth. Epoch of Eruption. Tooth. Perma- nent Molars. Girarb. Mayhew. Inferior Molars. Superior Molars. Secellier. 4th 5th 1st 1st and 2d 2d and 3d 6th 10 months. 20 months. 30 and 32 mos. 36 months. 4 and 6 years. ....... 12 months. 18 and 24 mos. 36 months. 4th 5th 1st and 2d 6th 3d 4th 5th 1st 6th 2d 3d 10 and 12 mos. 20 and 24 mos. 30 and 36 mos. 32 and 36 mos 40 and 42 mos. 44 and 48 mos. 6th and 3d 60 months. According to Secellier, the inferior milk-molars fall con- stantly before those of the upper jaw, w^iile the eruption of the permanent molars of both jaws takes place at the same time. DURATION OF THE LIFE OF THE HORSE. According to Biiffon, the duration of the Hfe of the horse is, as in all other species of animals, proportionate to the dura- tion of its growth. Man, who is fourteen years in growth, lives six or seven times that length of time ; that is to say, he may live to 90 or 100. The horse, which requires about four years to attain its growth, may live six or seven times that length of time ; that is, to twenty-five or thirty years. Examples which are contrary to this rule are so rare that they need hardly be regarded as exceptions of consequence ; as the more common draft-horses acquire their growth in less time than better-bred horses, they also live a shorter time, — fifteen or sixteen years. According to Bourgelat, " the age of the horse can be esti- mated at eighteen to twenty years. The number of those which pass this age is excessively small." Aristotle noted that horses which are nourished in stables live for a shorter time than those which are raised in herds ; the conditions of slavery and domesticity diminish their powers of resistance to the wear and tear of life. Athenseus and Pliny claim to have known the horse to attain the age of sixty-five or even seventy years. Augustus Nipheus speaks of a horse belonging to Ferdinand I which was over seventy, but these observations are only exceptions similar to those which we sometimes find in the human species. Hartman and Buffon both note that the life of mares is generally longer than that of horses. This observation was already made by Aristotle (Hist. Animal., lib. v), and corre- sponds to the same rule in the human race, where women gen- erally live to a greater age than men. Hartman claims that it is "an undoubtable sign that a breeding horse is well bred and in good health when it is slow in development. Those which do not attain their complete growth until six or seven years, ex- cepting in cases of accident, are useful for twenty years or more, (46) OF THE COLLEGE OF ^^ULTU^ DURATION OF THE LIFE OF THE HORSE. ^1 and may still be sound and healthy at thirty years. The other ones, on the contrary, — those which attain their growth in four years, — rarely pass the age of twenty." The great, heavy draft-horses, which attain their growth in even less time, are already aged at ten or twelve years. Exam- ples of horses of thirty, thirty-six, and forty years of age would not be so rare among our animals if the tyranny and hard usage imposed upon them by men did not aid greatly to shorten their lives. Ordinarily, as soon as a horse has seen its best days, it is sold from the stable in which it has been kept, to be replaced by more useful animals, and it goes rapidly into the hands of the hackman and the huckster, doing harder work with less nour- ishment, until it becomes completely used up, and depreciates to the value of the knacker's price. Among the principal causes which modify the longevity of the horse may be counted the length of time of development, the size of the horse, the work to which the animal is put, and the care which it receives. We find certain races and certain individuals which are pre- cocious in their development, and other races and subdivisions of families in which longevity is hereditary. M. Bouley says : " There are tardy races and precocious races. In the last the precocity is the result of the combined influence of heredity and alimentation, in which the organic formation acts in a precipitous way, as it were, in those in- dividuals which compose it, and we find a hasty achievement of development ; from which it results that the duration of their first part of life is so much shortened, and, as a fatal conse- quence, also that of their whole life ; for this more rapid de- velopment, impressed on their organisms, has no other termina- tion, from the industrial point of view, which produces it, than to hasten the moment of death." The small races of horses and small individuals last usually for a longer time than larger ones. We can make no satisfac- tory explanation of this, unless it is that in the larger animals the wear and tear is greater from the very fact of the animal 48 AGE OF THE DOMESTIC ANIMALS. having so much more to take care of in itself. The character of work to which the horse is put is an important factor in shortening the Hfe, — due to the fatigue entailed and the using up of the powers of the organs. We find that a horse with a quiet and docile disposition will perform heavier and rougher work, with less deterioration in its animal economy, than one alongside of it of a nervous and excitable disposition. The more calm and quiet life of horses in the country is less prejudicial to their existence than the bustle and confusion of the great industrial centres and crowded streets of our large cities. Again, the necessities of rapid and variable work and irregular hours of feeding in great cities predispose to internal diseases, while the greater loads and rough pavements lead to strains of tendons, wrenches of bones, bruised feet, and other injuries which soon render the animals unserviceable, or condemn them to return to the softer ground, lighter work, and more regular life of the country, with, however, a broken-down con- stitution. The care which the horse receives from its keeper — which, of course, includes the regulation of work and feed — is an all-important matter. A kind, judicious owner will work horses for years and keep them sound and in good condition, doing a vast amount of work; while in the next stable, under the guid- ance of a careless or brutal owner, equally good horses will perform less work and become worthless in a short time. The word ''iised^^ applied to horses has become synony- mous with the word " aged " applied to man, and indicates the time when the animal has become prematurely old. Examples are not rare in which the horse has attained the age of thirty, thirty-six, forty, and even more years, and has been in perfect health and capable of moderate useful service. PRINCIPLES OF EXAMINATION FOR DETERMINING THE AGE OF THE HORSE. To any one accustomed to horses it is an easy matter to dis- tinguish at sight the very young from the adult horse, and the middle-aged from the very old animal. In very old animals white hairs commence to show in the neighborhood of the PRINCIPLES FOR DETERMINING THE AGE OF THE HORSE. 49 temples and around the eyes and the nostrils, if the color of the animals is dark ; gray and roan horses become very much lighter in color, and even at times nearly white ; the inferior extremity of the head becomes pointed, and the sides of the face become depressed ; there is an evident change in the line of the back and loins, which become depressed (sway-backed). The aplomb of the legs and the blemishes found on them are common witnesses of work which has lasted for a number of years. In addition to the examination of the teeth, which is frequently considered the only point that need be looked at to determine age, there are many other points which are of very great value. We have seen that the molar teeth of the very young animal are deeply imbedded in the alveolar cavities of the jaw- bone, and that when the animal becomes older the teeth are gradually pushed out from these cavities as the free extremities of the tooth become worn away. The molars are pushed out and the jaws become thinner by absorption of the bone, which is no longer needed as a bed for holding the teeth, which are dimin- ished in size. We find, then, that, as the horse becomes grad- ually older, the branches of the jaw-bone, which in the young animal were thick and rounded, become gradually thinner and sharp on their border, and form a very accurate indication of the approximate age of the animal. In an old Arab book of agriculture, by Ibn-el-Awamm, written about the twelfth century, it is stated that "one of the signs by which an old horse can be recognized is to pinch be- tween the thumb and index finger the skin of the forehead and draw it out, and then to let go of it quickly. If the skin re- turns promptly to its place and becomes perfectly smooth, the animal will make a good horse," etc. In Aristotle we find the same statement prescribed as an indication of age: "If the skin returns promptly to its place and leaves no wrinkle, the animal is young ; if the skin remains wrinkled, it is old." An old and neglected, but useful, means of approximating 50 AGE OF THE DOMESTIC ANIMALS. the age of old horses is by means of the " knots " in the tail. Tliese knots are little, prominent eminences on either side of the base of the tail, formed by the transverse process of the coccygeal bones. The processes can be felt in young horses, and become especially prominent after the emaciation of a severe illness, but in this case they are rounded and are apparently continuous with the other tissues, while in old horses, due to absorption in the bone itself, they become more distinct, and seem to stand out in the muscles and softer structures of the tail. The knots are felt distinctly at the base of the tail when the horse has attained the age of thirteen years. In two years later, when they have become more prominent, they have be- hind them a distinct little depression two or three lines in width. At sixteen a second pair of knots are found, which, like the firsts in about two years, have behind them a distinct depression, and so on, every three years, a new pair of knots furnish an approxi- mately accurate indication of the age of the animal. The teeth, however, are by far the most important wit- nesses of the age of the horse. The examination of these^ which includes the incisors, the tusks, and the molars, shows (a) if the incisive arch is composed of teeth of the first or second dentition, or of both ; (h) if there is a normal number of them ; (c) the situation, length, breadth, and the angle v/hich they have in the maxillary bones ; (d) if the tables of the teeth touch each other, or if one overreaches the other, which somewhat modifies the leveling of the table; (e) the color and substances on the face of the teeth; (/) if they have been subjected to fraudulent handling. In the incisors we study the form and details of the table, the direction and length of the tooth, and the condition of the corner tooth. In the tusks we note the amount of use to which the teeth have been subjected, their direction and their length. In the molars we look for the number and the dentition to which they belong, the condition of their grinding surface, their length and direction and the integrity of their substance, and that of the gums which surround them. CHARACTERS FURNISHED BY THE TEETH. 51 CHARACTERS FURJTISHED BY THE TEETH. The reader may, perhaps, have wondered why we should have gone into such minute detail in the anatomical description of the teeth, but an accurate knowledge of all these details is absolutely necessary, when we take into consideration the slow, insensible, and variable wearing, producing ^often only trivial changes, which are, however, important guides. Washed incessantly, rubbed, used, and broken as the teeth are by the action of the saliva, the lips, the cheeks, the tongue, and the food which the animal takes, we have to take into con- sideration every detail of their structure, their position, the breed and general condition of the animal, and the surroundings in whicli it has been raised. A thoroughbred with dense bones and hard teeth will wear the latter away much more slowly than a coarse-boned, lymphatic, common horse with softer substances in the teeth. The character of food to which a colt has been accustomed will stimulate or diminish the functional activity of the tooth, and, while hard substances would naturally wear a tooth faster than softer food, yet the animal which has been raised on the former will often have harder teeth than one which has not had to use them so severely. Any one who has only been* accustomed to examine the mouths of horses of one section of country will find that he must extend his ideas and adapt himself to a new condition of things, when called upon to judge of the age of horses from another region. If a horse's mouth presents exactly the characters which indicate a certain number of years of growth, we say that it " is — years ;" if it has not quite attained the age, it is described as " rishig — years;" if it has passed the period and has not yet attained the markings of another year, it is counted as " — years off," The natural division of the two periods of age, as indicated by the temporary and the permanent teeth, is subdivided as follows : — 1. The period of eruption of the incisors of first dentition. 52 AGE OF THE DOMESTIC ANIMALS. 2. The leveling of these teeth and their progressive use. 3. The period of the falling out of the deciduous teeth and the appearance of the permanent ones. * 4. The leveling of these latter. 5. The successive forms which their tables present as the teeth become worn away. FIRST PERIOD. ERUPTION OF THE INCISORS OF FIRST DENTITION. At Birth, — At the birth of the foal the incisors have not yet pierced the gums. The anterior border of the pincher and intermediate teeth can be seen under the mucous membrane, which is rendered paler than the surrounding tissues by their pressure. (Figs. 32, 33, 34.) About One Week. — The pincher teeth have generally ap- peared in from six to eight days, the upper teeth preceding the lower by twenty-four or forty-eight hours. At this age the teeth are of little importance; for the general aspect of the animal, its manner of walking, which is still unsteady, and the condition of its hairs show that it is but a few days old. (Figs. 35, 36, 37.) About One Month. — The intermediate teeth appear between thirty and forty days, just as the interior border of the pincher teeth commence to be worn. (Figs. 38, 39, 40.) About Three Months. — There are now four teeth in the upper and four teeth in the lower jaw ; the pinchers have com- menced to wear on their posterior borders ; they are entirely free from the gum. (Figs. 41, 42, 43.) About Four Months. — The incisive arch has become wider ; the inferior intermediate teeth are free from the gum; their anterior border has commenced to be worn away toward their inner edge as it comes in contact with the corresponding supe- rior teeth. (Figs. 44, 45, 46.) About Five Months. — The pincher teeth have pushed through the gums to the line of the neck of the teeth ; the intermediate teeth are worn on their anterior borders ; the mucous membrane is ollen sensitive along the posterior border of these teeth on account of the corner teeth, which have commenced to push out. (Figs. 47, 48, 49.) (53) 54 AGE OF THE DOMESTIC ANIMALS. About Six Months. — The intermediate teeth have pushed farther out ; their posterior borders have come in contact with each other. In the region of the corner teeth the mucous mem- brane is puffy and congested ; sometimes even at this age the anterior border of the corner teeth shows under the soft tissues. About Eicjlit to Ten Months. — The anterior borders of the corner teeth are seen through the mucous membrane. The in- termediate teeth are entirely through the gums to the level of their neck. The inferior incisive arch forms a regular half- circle. (Figs. 50, 51, 52.) It is not important to be more precise at this age, as various causes influence and produce slight variations in the eruption of the teeth and in their leveling. Some animals are strong and vigorous, while others are weak and feeble ; some have been well fed, while others have been nourished badly; and, again, we find individual peculiarities of precocity and tardiness in the eruption of the teeth as in other evidences of development. At the outset, the foal only uses the milk of its mother; at this time there is little friction and using of the teeth, except from their simple position and con- tact with each other. As the foal gets older and commences to use fibrous and resisting food the incisors wear away more rap- idly; there is always the most use in the pincher teeth. INIore- over, during this first period of the life of the animal, while it is still with its mother, other conditions allow us to judge with sufficient accuracy as to the age of the animal, which is not ready to be sold or removed until it has been weaned. AT BIRTH. 55 Fig. 32. Fig. Fig. 34. At Birth (Figs. 32, 33, 34).— The incisors Jire not yet out. The m neons membrane still covers the teeth, which are about to appear. In front are seen under the gums the two pinchers, aboA^e and below. In profile are seen the intermediate teeth, less developed than the pincher teeth. The jaws are rounded. The dental table shows on the side a. little ridge formed by the anterior border of the pinchers, with a less distinct elevation for the intermediate teeth on the side; the edge of the teeth near the symphysis of the jaw is higher than the outer edge, and comes throuoh first. 56 AGE OF THE DOMESTIC ANIMALS. 4> Fig. 35. Fig, Fig. 37. One Week (Figs. 35, 36, 37). — The pincher teeth are through the gnms. In face, the anterior borders are seen. In profile, the gums are thinned on the intermediate teeth. The tables show the anterior borders of the pinchers through and depressions over the posterior borders. ONE MONTH. 57 Fig. 38. Fig. 39. Fig. 40. One Month (Figs. 38, 39, 40). — In front the pincher teeth, which appeared during- the first week, are in contact with each other; their anterior face is striated with little gutters. On the side, tlie anterior border of the intermediate teeth is seen. In profile, the jaws ;ne seen thicker?^ the gums still cover part of the anterior face of the inter- mediate teeth. The dental tables are uncovered in the pinchers. There is a slight use of both borders of the teeth above ; below, tlie anterior border only has been worn. The membrane still covers tlie posterior border of the intermediate teeth and a portion of their dental cup. 58 AGE OF THE DOMESTIC ANIMALS. P'IG. 42. Fig. 43. lliree Months (Figs. 41, 42, 43). — From in front, the pinclier teeth are seen almost entirely free, though the gums still encircle the base of their free portion. The intermediate teeth are in contact by the internal portion of their anterior border. In profile, the jaws are seen wider, thicker, and less curved ; the intermediate teeth are not yet completely free. Their free borders are separated behind ; the dental tables are slightly used ; both borders of the intermediate teeth are slightly worn toward their inner edge. The incisive arch increases in extent trans- versely. FOUR MONTHS. 69 Fig. 41 Fig. 45, Fig. 46. Four Months (Figs. 44, 45, 46). — From in front the transverse diameter of the jaws is increased ; the intermediate teeth are further out. 60 AGE OF THE DOMESTIC ANIMALS. Fig. 47. Fig. 4h. FIVE MONTHS. 61 Fig. 49. Five Months (Figs. 4t, 48, 49). — The jaws are thicker and the in- cisive arch is wider transversely. From in front the intermediate teeth are seen almost entirely free. In profile these teeth are in contact by the whole extent of their anterior border ; the table of the pinchers are more worn, especially above. In each jaw the anterior border of the intermediate teeth is worn almost for its whole length ; the posterior border is less worn. Below is seen, under the mncous membrane, the internal edge of the corner teeth, which are preparing to pierce through. They form a little elevation of the mucous membranes placed imme- diately behind the internal border of the corresponding intermediate teeth. 62 AGE OF THE DOMESTIC ANIMALS. Fig. 50. Fig. 51 TEN MONTHS. 63 Fig. 52. Ten Months (Figs. 50, 51, 52). — These jaws come from a pony which was rather tard}' in marking its age ; nevertheless, they are useful plates from which to study the diverse characters of this period. The pinchers and intermediate teeth are entirel}^ free from the gum ; the anterior face of these teeth is polished, the little striations or canals are less visible; the intermediate teeth, which have been in contact for some months, are worn on both borders. The corner teeth are just appearing, but are not yet in contact with each other. The wearing of the pincher teeth is greater than that of the intermediate teeth. SECOND PERIOD. LEVELING, PROGRESSIVE USE, AND FALLING OUT OF THE INCISORS OF FIRST DENTITION. About One Year. — The corner teeth have protruded from the gums, but the inferior ones are not yet in contact with the superior teeth. The inferior pinchers, if not leveled, are at least very much used on both their borders. The incisive arch com- mences to be a little depressed in the centre. The superior pinchers and intermediate teeth just commence to wear at their posterior borders. (Figs. 53, 54, 55.) About Sixteen Months. — The superior corner teeth meet the inferior and commence to wear at their anterior border; the necks are clear of the gums. Often at this time the inferior pinchers are leveled, but the intermediate teeth are rarely more than slightly worn. The incisive arch is flattened in front. (Figs. 56, 57, 58.) About Twenty Months. — The inferior corner teeth are nearly leveled; the superior ones are less so. The inferior pinchers stand out from the gums, and the intermediate teeth are often leveled. The incisive arch becomes less convex. (Figs. 59, 60,61.) About Two Years. — The inferior dental arch is completely leveled at the pinchers and intermediate teeth, and the superior arch is nearly so. The superior pinchers stand out from the gums, and behind them is found a moderately sensitive swelling, — due to the permanent teeth, which are pressing on the gum of ^the palatine arch. The intermediate teeth are free from tlie gums above and below. The incisive arch has widened from side to side and the pinchers and intermediate teeth form almost a straight line. (Figs. 62, 63, 64.) (64) LEVELING, PROGRESSIVE USE, ETC. 65 Girard thought that the pinchers were leveled at ten months, the intermediate at one year, and the corner teeth at fifteen to twenty-four months, but this is too definite; the leveling of the temporary incisors is somewhat irregular, and is considerably modified by the depth of the cups, the amount of cement which they contain, and the character of the food upon which the animal is fed. Experience will teach the observer to place much value on the condition of the corner teeth, the amount of wear of the superior incisors, and upon the color, which gradually becomes darker. At the end of this period the pinchers become broken, loose, and ready to fall from their sockets ; they are less solidly fixed in the jaw and may be broken ofi", or are pushed out naturally by the permanent teeth, which replace them. During this period, especially during the second year, the variations in the amount of wear of the teeth in different animals may be very marked ; but, by a careful comparison of the use which each pair of teeth — pinchers, intermediate, and corners — have undergone, and, with close observation of the development and size of the bones, taking into consideration the intermaxil- lary bones, and the width and thickness of the body and branches of the maxilla, a very close differentiation of a month or two may be made. Especial note must be made of the amount of gum which still covers the crown of the teeth, or their freedom from the gums, the discoloration on their surface, the polishing off* of the small striations, and the evidence of the protrusion of the permanent teeth under the gums behind the deciduous teeth. 66 AGE OF THE DOMESTIC ANIMALS. Fig. 53. Fig. 54. ONE YEAR. 67 FiO. 55. One Year (Figs. 53, 54, 55). — All of the deciduous incisors can be seen from in front ; the pinchers and intermediate teeth are entirely free from the gums. In profile the superior corner teeth are not yet in con- tact with the inferior teeth. The tables show a decided use on the pos- terior borders of the intermediate teeth, which, however, is subject to variation, according to the height of the posterior border in different colts. There is generall}'^ seen at this time in. the anterior border a yellow line, elongated transversely^ which represents the elementary dental star. The corner teeth are still virgin. Comparison must be made between the wear of the pincher teeth and that of the borders of the intermediate teeth, and according to the amount of use which the latter have had the animal can be judged as rising or off the age indi- cated by the other marks. 68 AGE OF THE DOMESTIC ANIMALS. Fig. 56. Fig. 57. SIXTEEN MONTHS. 69 Pig. 58. Sixteen Months (Figs. 56, 57, 58). — All of the teeth are in contact. The superior corner teeth are in apposition with the inferior, and have commenced to be leveled in both jaws ; the enamel of the cups and the peripheral enamel are separated ; the crown of the tooth is entirely free from the gum. Often at this period the inferior pinchers are leveled, and sometimes tlie inferior intermediate teeth are also leveled. In the upper jaw the tables of all teeth are entirely formed, the incisive arches lose their convexity. 70 AGE OF THE DOMESTIC ANIMALS. Fia. 59. Fig. 60. TWENTY MONTHS. 71 Fig. 61. Twenty Months (Figs. 59, 60, 61). — This mouth comes from a thoroughbred colt, which was. grain-fed from birth. It represents more use than should be at this age. The inferior corner teeth are leveled on their anterior border ; the superior corners are somewhat worn, but not even comparatively to the degree of use of the pinchers and interme- diates. The inferior pinchers are completely worn, and the inferior in- termediate teeth are leveled ; the incisive arch has become less convex, but not wide enough for a two-year-old ; a bit of the gum still remains around the roots. 72 AGE OP THE DOMESTIC ANIMALS. Fig. 63. TWO YEARS. 73 Fia. 64. Two Years (Figs. 62, 63, 64). — This mouth comes from a common- bred colt which had no grain feed. It was two years and twenty-six da3's old. From in front the pinchers and intermediate teeth are seen free from the gums, indicating that they are pressed on by the permanent teeth. In profile, the corner teeth are free to their necks. The tables are well worn, and the dental stars show. The cups of the superior intermediate teeth are free from the peripheral enamel. Tlie incisive arch is widened transversely. THIRD PERIOD. ERUPTION" OF THE PERMANENT OR ADULT TEETH. This period commences at the age of two or two and a half years, and finishes at five years. About Two and a Half Years. — Successive falling out of the temporary pincher teeth; swelling of the gums and appear- ance of the anterior borders of the permanent pinchers. Ordi- narily these teeth appear in the superior jaw first, and the piercing of the gums is completely effected in about six weeks to two months. Rising Three Years. — As the colt is approaching the age of three years, we find in the superior jaw the permanent pinchers wholly out of the gums and almost reaching the level of the temporary intermediate teeth. In the inferior jaw, the borders and sometimes a greater extent of the free extremities of the teeth have appeared through the gums, though the teeth are still virgin ; the intermediate temporary teeth are free from the gums at their neck, and very much worn. The corner teeth are worn so that they touch each other by their external borders. (Figs. ^^, m, 67.) Three Years. — At three years of age all of the permanent pinchers are out of the gums and have reached the level of the temporary teeth. The permanent pinchers are wider trans- versely, square, and darker in color than the temporary teeth, and show little gutters on their anterior face. They differ dis- tinctly from the others, which are smaller, more convex, have a constriction in the neighborhood of the gums, are whiter, and are not marked with gutters. (74) ERUPTION OF THE PERMANENT OR ADULT TEETH. 75 The time of the year and the race of the animal must be taken into consideration in determining the completion of three years. The better breeds of horses attain that age in mid- winter, while those of more common races do not attain it until the months of March, April, or May. Three Years Off. — When the colt is several months from three years of age the permanent teeth are well used on their borders and in contact with each other, but the dental cups are not yet complete circles, as the enamel which forms them is still connected with the peripheral enamel toward the borders of the teeth. The intermediate teeth are very much worn, protrude from the gums, and are sometimes broken and ready to fall out. The tables of the corner teeth have become very much larger and almost cover the external borders of the teeth. (Figs. 68, 69, 70.) Rising Four Years. — Eruption of the permanent inter- mediate teeth and progressive falling out of the temporary inter- mediate teeth mark this period. The permanent intermediate teeth appear, but have not yet reached the level of the tables of the corner teeth, and are not yet worn. The central enamel in the pincher teeth surrounds the dental cup, which is flattened from in front to behind, and is almost distinct. The corner teeth commence to be free at their necks from the gums. (Figs. 71, 72, 73.) Four Years. — Each jaw shows four permanent teeth, with their tables on the same level ; the intermediate teeth are worn both on their anterior and posterior borders, but the dental cups are not entirely separated from the outside peripheral enamel. Often the inferior pincher teeth are leveled, especially in well- bred horses. The temporary corner teeth stand out from the gums and are completely worn. (Figs. 74, 75, 76.) Four Years Off. — Loosening and successive falling out of the temporary corner teeth, which are worn to stumps, scarcely fastened in their alveolar cavities. Sometimes one or more of 76 AGE OF THE DOMESTIC ANIMALS. the corner teeth have fallen out, and we find the mferior borders of the permanent corner teeth appearmg first, more frequently in the upper jaw. The pinchers and intermediate teeth are well worn. At this period we frequently find anomalies in the eruption of the teeth. It is not rare to see the intermediate and corner teeth appear at the same time ; so that an animal which is only four or four and a half years of age may have the teeth which ordinarily indicate five years. (Figs. 77, 78, 79.) Rising Five Years. — The four temporary corner teeth have fallen out and are replaced by the adult teeth. These last have not yet reached the level of the intermediate teeth and are not yet worn. The pinchers are leveled; their central enamel, elongated from side to side, is found farther and farther* away from the anterior border of the dental table. The tables of the intermediate teeth are distinctly formed. (Figs. 80, 81, 82.) Five Years. — The mouth is complete ; the incisive arch is semicircular and regular in shape ; all of the permanent teeth have reached the same level. The anterior borders of the corner teeth are completely worn. The posterior are not yet worn. (Figs. 83, 84, 85.) Five Years Off. — The above characteristics are more distinct. The age has been more marked by the continual friction and amount of work to which the corner teeth have been subjected. In the superior incisive arch, the posterior borders of the corner teeth rarely commence to be worn. The profile of the incisives shows a regular one-half circle, convex from above to below. During this period, besides the causes already referred to which produce hasty or tardy eruption of the permanent teeth, other influences may act. Traeger, veterinarian at Doehlen, noticed that gestation in the young mare delayed the eruption of the permanent teeth ; he also observed that continuous preg- nancies diminished the wearing of the teeth. During this pe- riod the tusks may make their appearance, or they may be delayed until after all of the incisors are in place. In cases of doubt, a further examination should be made as to the con- ERUPTION OF THE PERMANENT OR ADULT TEETH. 77 dition of the molars. By reference to the table of the eruption of these teeth it will be seen that the first permanent molar appears between the thirtieth and thirty-second months, the second at about three years, and the third at four to five years. The same rule as given for the second period applies here also, and a close comparison should be made of the comparative wearing of the pincher, intermediate, and corner teetli, as the first or second pair may be advanced in use and not correspond to the freshness of the delayed later teeth. 78 AGE OF THE DOMESTIC ANIMALS. Fig. 66. RISING THREE TEARS. 79 Fig. 67. Bising Three Years (Figs. 65, 66, 67). — From in front, in the upper jaw, the two permanent pincher teeth are seen not yet opposite to the level of the intermediate deciduous teeth ; below, the adult pinchers are just coming through the gum, showing a small portion of their anterior face. In profile, the intermediate teeth are very much worn, and the constriction on their neck is pushed out beyond their gums ; the corner teeth are much shortened ; the dental table shows slight wear of the superior pinchers, which has been produced by the eruption of these teeth before the inferior temporary pinchers had fallen out, and, conse- quently, they have worn against the latter. The intermediate teeth are completely leveled ; the corner teeth are much used. 80 AGE OF THE DOMESTIC ANIMALS. Fig. 68. Fig. 69. THREE YEARS OFF. 8t Fig. 70. Three Years Off (Figs. 68, 69, 70).— From in front the four per- manent pinclier teeth are seen, much larger and stronger than the neigliboring teeth. The anterior borders of the superior pinchers are oblique, and their external borders are not yet in contact with the cor- responding part of the inferior teeth. In profile, the intermediate teeth are seen much used ; the corner teeth are short, and show the constric- tion at their neck. The tables are worn off level. Between the corner and the intermediate teeth on the left is seen the protrusion of gum made by the permanent intermediate tooth which is shortl3'^ to appear. The dental tables of the inferior intermediate teeth are very much worn, the superior teeth somewhat less so. The inferior corner teeth are entirely leveled. In this mouth the tables of the inferior pincher teeth nvQ the most worn, as these teeth came out before the suj^erior ones did. 82 AGE OF THE DOMESTIC ANIMALS. Fig. 71. Fig. 72. RISING FOUR TEARS. 8^ Fig. 73. Rising Four Years (Figs. Yl, 72, 13). — From in front are seen tlie eight adult incisors ; the pinchers in contact with the opposite ones, and intermediate teeth not 3'et out to the level of the pinchers. In profile, this is also seen in this mouth. The corner teeth are very much worn ; the tables of the pinchers are considerably worn, making almost a com- plete separation of the central, or cup, enamel from the peripheral enamel. This advanced wear of the pincher teeth is not in direct harmony with the amount of use of the corner teeth. w AGE OF THE DOMESTIC ANIMALS. Fig. 74. Fig. 75. FOUR YEARS. ^ Fig. 76. Four Years (Figs. 74, 75, 76). — From in front the four superior per- manent teeth are seen in contact with the inferior teeth. The jaw has at- tained such a width that the corner teeth are almost hidden. In profile, the latter are seen to be very small. The superior ones have commenced to be pushed out from the jaw. In the lower jaw are seen the tush teeth. The tables of the intermediate teeth are much worn, especially in the upper jaw, in which the eruption took place first. The central enamel is only separated in the superior left-hand teeth ; the inferior corner teeth are almost leveled, the superior ones completely so. The latter are being pushed out, and show their roots. 86 AGE OF THE DOMESTIC ANIMALS. Fig. 77. Fig. 78. FOUR YEARS OFF. 87 Fig. 79. Four Years Ojf (Figs. 77, 78, 79). — In front the intermediate per- manent teeth are seen in contact with each other ; the inferior and superior left-hand permanent corner teeth have appeared. In profile, it is seen that these teeth have not been completely pushed through the gums. The tush teeth have appeared. The right-hand superior milk- tooth is ready to fall out ; nothing remains but its roots. The inferior tooth on the same side is leveled, but still firmly imbedded in the jaw. The superior intermediate teeth, which preceded the eruption of the inferior teeth, show considerable wear. The cups have formed in the pincher teeth. 88 AGE OF THE DOMESTIC ANIMALS. FlQ. 1 Fia. 81. RISING FIVE TEARS. 89 Fig. 82. Rising Five Years (Figs. 80, 81, 82). — The four corner teifiporary teeth have been replaced by the permanent teeth, but these are not on a level with the intermediate and are entirely virgin. The tables of the other teeth show a more decided use than those in the last figures. Above, the cups are formed in both the pincher and intermediate teeth ; the cups are nearly formed in the inferior intermediate teeth. 90 AGE OF THE DOMESTIC ANIMALS. Fig. 83. Fig. 81 FIYE YEARS. 91 Fig. 85. Five Years (Figs. 83, 84, 85). — The mouth is entirely made ; all of the permanent teeth have reached the same level in both jaws. The jaws are convex in both directions ; the tush teeth have completed their eruption. The corner teeth have commenced to wear on their anterior border; the pincher teeth are leveled, but the cups are still elongated from side to side and are ver}^ narrow ; they commence to approach to the posterior border of the teeth. This form of cup indicates that in these teeth the cups are very shallow. The incisive arches form a regular half-circle. FOURTH PERIOD. LEVELING OF THE PERMANENT INCISORS. During this period the signs furnished by the dental appa- ratus become more difficult to recognize, and the determination of the exact age is less precise than at an earlier period. The points to be examined from six years are, first, the wearing of the corner teeth, the form of the transverse diameters of the teeth, the position of the central enamel on the surface of the table, and the general outline of the incisive arch. At six years, after the complete leveling of the teeth, the tables of the pinchers commence to become oval in shape. The posterior border of the corner teeth has become worn and the cup is completely separated from the peripheral enamel. The cement disappears from the anterior face of the pinchers, so that they become whiter in color. Very frequently at this age the notch commences to show on the outer border of the superior corner teeth. At seven years, all of the teeth are denuded of cement on their outer faces and are much whiter in color. The inferior corner tooth, which is narrower from in front to behind than the superior, wears only the anterior portion of the latter and makes distinct, in profile, the notch which we have just seen often commences at six. The pincher teeth become narrower from side to side, and the oval of the posterior border shows a pro- jection backward ; the intermediate teeth become oval, and, in both, the cups become decidedly naiTower and are found nearer the posterior border of the teeth. In profile, the incidence of the jaws has altered from the convex arch of six years and tends to assume the form of an ogive. At eight years, the incisors commence to turn from a white to a yellowish white. The arches are narrower from side to (92) LEVELING OF THE PERMANENT INCISORS. 93 side, the obliquity of the teeth is greater, and, as the inferior corner teeth now commence to wear by their posterior borders, their tables become elongated and correspond to the tables of the superior corner teeth in size, so that the notches of the latter become less marked. The interspaces between the teeth become more marked and the gum commences to retract from the crowns, giving a square cut-off appearance. The tables become more convex on their posterior borders, and the cups, which continually approach the posterior borders of the teeth, in the pincher teeth become convex behind. In front of them, half-way to the anterior border of the teeth, a transversely elongated dark- yellow line appears. This is the dental star, brought into view by the uncovering of the calcified dental pulp. If the structure and formation of the incisive teeth are remembered, the exact value of the dental star will be better appreciated. In the virgin tooth the upper extremity is hollowed by the cup, and the dental pulp occupies the space between the anterior face of the cup and the anterior face of the tooth itself But we have seen that the cup, pointing downward, also inclines toward the posterior border of the tooth. At eight years the cup is at the division of the posterior and middle thirds of the table of the tooth, and the dental pulp is found on the line between the middle and anterior thirds. The transverse extent of the dental star is much less in the intermediate and corner teeth than it is in the pincher teeth. 94 AGE OF THE DOMESTIC ANIMALS. Fig. 86. Fig. 87. SIX YEARS. 95 Fig. 88. Six Years (Figs. 86, 87, 88). — In front, the teeth appear much as they were at five years of age. In profile, we see in this animal a more tardy eruption of the tush teeth, which are not yet quite free from the gums, and are, therefore, of little value as regards the age. The tables furnish a most accurate guide ; the posterior border of both inferior and superior corner teeth are worn ; the pincher teeth are leveled and their tables tend to an oval form. It is seen, however, that the inferior cups are thicker at their anterior borders, — due to a small portion of the sur- face enamel still remaining. The cups are narrower from side to side than at five years, and somewhat closer to the posterior border of the table ; the same appears on the intermediate teeth. It will be noticed that the cups of the superior corner teeth have fissures on their poste- rior borders, which is of frequent occurrence and does not interfere with judging the amount of work which they have performed, 96 AGE OF THE DOMESTIC ANIMALS. Fig. 89. SEVEN YEARS. 97 Fig. 91. Seven Years (Figs. 89, 90, 91). — There is nothing special to be seen in front except that the teeth are whiter, — due to the disappearance of "the cement, which has been worn from the surface of the enamel. In profile it is seen that the table of the inferior corner tooth is narrower than that of the superior from the front to behind, so that a notch is formed on the posterior corner of the latter. The incident of the tooth is less perpendicular than at six years. The cups of the tables of the intermediate teeth are wider from in front to behind and narrower from side to side. In the corner teeth the wearing surface is larger and the •cups are smaller. The pincher teeth are oval and the intermediate teeth •commence to become so. In this mouth, again, the superior corner teeth iire fissured on their posterior borders. 7 98 AGE OF THE DOxMESTIC ANIMALS. Fig. 92. Fig. 93. EIGHT YEARS. 99 Fig. 94. Eight Years (Figs. 92, 93, 94). — The direction of the incisors is decidedly changed ; the inferior and superior iirches ure opposed ob- liqnel}^ ; seen from in front, the teetli project at the line of apposition. In the profile this is more apparent, and the arch assumes more the form of an ogive. The incisive arches are still regular, but decidedly smaller than the earlier ages. All of the inferior tables are leveled ; the pincher and intermediate teeth are oval, the corner teeth begin to become so. The cups commence to assume an angular form behind, and are narrow. The dental star has appeared in the pinchers and commences to show in the intermediate teeth, between the anterior border of the table and the corresponding part of the cup. FIFTH PERIOD. WEARING AWAY OF THE CROWNS. After this time, which is commonly known as " past mark of mouth," commencing at nine years and extending to old age, the regularity of the wearing of the teeth and the certainty of the signs of age furnished by tliem become more variable. The uncertainty increases greatly after fifteen years, and a year or two later the estimation of age from the teeth can only be a conjecture, based upon experience and subject to error of one, two, or even several years, which becomes greater the older the animal is. The changes of this period are : The successive alteration in shape of the tables of the teeth ; the position of the cups in the incisors of both jaws ; the form and location of the dental stars in the tables ; the obliquity or degree of incidence in the incisive arches ; the convergence of the crowns and the narrow- ness of the jaw holding the roots ; the thickness of the enamel on the anterior and posterior faces of the teeth ; the appearance of the cement around the roots ; and, the shape of the bones of the face and jaw. At nine years^ the pinchers are round ; their cups are tri- angular and their dental stars are more distinct, but narrower. The intermediate teeth commence to become round and the comers oval ; the superior pinchers are often leveled ; the notches on the superior corners often disappear. At ten years^ the tables of the pinchers are decidedly I'ound ; the cups are very small and distinctly triangular. The interme- diate teeth assume the shape of the pinchers the previous year. The dental star is nearly in the middle of the table. At eleven years^ the corner teeth are rounded. The cups are only small spots near the posterior borders of the tables ; the dental stars are in the middle of the tables. The inferior (100) WEARING AWAY OF THE CRO\yyS. 101 comers are as large at the gums as at tlieir free extremities, and notches re-appear on the superior corner teeth. At ticelve years^ all of the teeth are round ; only a trace of the cups remains in the inferior ones. The superior corners are leveled. Both incisive arclies are much narrower and the tongue shows over their borders. The inferior border of the jaw-bone becomes sharp, and a flattening of the sides of the face, over the roots of the superior molars, is seen. The inci- dence of the incisive arches increases, especially if the teeth are unusually long. At thirteen years^ the signs of twelve years are more marked. The notch on the superior corner teeth is greater. The cups usually disappear from the inferior incisors at this age, and the superior pinchers become round. At fourteen years^ the pinchers become triangular ; the incisive arch is depressed in front and becomes decidedly narrower. At fifteen years, the intermediate teeth commence to become triangular. The dental star is round in all the lower teeth and is dark and distinct. The cups of the upper teeth are smaller in size. At sixteen years, the intermediate teeth are triangular. At seventeen years, all of the lower teeth are triangular, and the dental stars are small and round. The cups of the upper corner teeth have disappeared and those of the others are round. After nineteen, the cups have usually all disappeared, the teeth approach a line parallel to the bones of the jaw, which is especially marked in the lower jaw, and the arches are flattened from side to side. The lower teeth may be worn almost to the gums, and deposits of cement around their roots may develop to supply a wearing surface. lOJ ALE OF THE DOMESTIC ANIMALS. Fig. 95. Fig. NINE YEARS. .103 Fig. 97. Nine Years (Figs. 95, 96, 97). — There is no special change to be «een from in front or in profile, although ordinarily the teeth are more obliqueh^ formed and less fresh-looking than at eight 3^ears of age. The notch on the superior corner has generally disappeared ; the tables, how-