Chapter III: Part 3

MAMARONECK, a township of Westchester county, New York, U.S.A., on Long Island Sound, about 20 m. N.E. of New York City and a short distance N.E. of New Rochelle. Pop. (1890), 2385; (1900) 3849; (1905) 5655; (1910) 5602. Mamaroneck is served by the New York, New Haven & Hartford railway. The township includes the village of Larchmont (pop. in 1910, 1958), incorporated in 1891, and part of the village of Mamaroneck (pop. in 1910, including the part in Rye township, 5699), incorporated in 1895. Larchmont is the headquarters of the Larchmont Yacht Club. The site of Mamaroneck township was bought in 1660 from the Indians by John Richbell, an Englishman, who obtained an English patent to the tract in 1668. The first settlement was made by relatives of his on the site of Mamaroneck village in 1676, and the township was erected in 1788. On the 28th of August 1776, near Mamaroneck, a force of American militiamen under Capt. John Flood attacked a body of Loyalist recruits under William Lounsbury, killing the latter and taking several prisoners. Soon afterwards Mamaroneck was occupied by the Queen's Rangers under Colonel Robert Rogers. On the night of the 21st of October an attempt of a force of Americans under Colonel John Haslet to surprise the Rangers failed, and the Americans, after a hand-to-hand fight, withdrew with 36 prisoners. Mamaroneck was the home of John Peter DeLancey (1753-1828), a Loyalist soldier in the War of Independence, and was the birthplace of his son William Heathcote DeLancey (1797-1865), a well-known Protestant Episcopal clergyman, provost of the University of Pennsylvania in 1827-1832 and bishop of western New York from 1839 until his death. James Fenimore Cooper, the novelist, married (1811) a daughter of John Peter DeLancey; lived in Mamaroneck for several years, and here wrote his first novel, _Precaution_, and planned _The Spy_.

MAMELI, GOFFREDO (1827-1849), Italian poet and patriot, was born at Genoa of a noble Sardinian family. He received a sound classical education at the Scolopi College, and later studied law and philosophy at the university of Genoa. When nineteen years old he corresponded with Mazzini, to whom he became whole-heartedly devoted; among other patriotic poems he wrote a hymn to the Bandiera brothers, and in the autumn of 1847 a song called "Fratelli d'Italia," which as Carducci wrote, "resounded through every district and on every battlefield of the peninsula in 1848 and 1849." Mameli served in the National Guard at Genoa, and then joined the volunteers in the Lombard campaign of 1848, but after the collapse of the movement in Lombardy he went to Rome, where the republic was proclaimed and whence he sent the famous despatch to Mazzini: "Roma! Repubblica! Venite!" At first he wrote political articles in the newspapers, but when the French army approached the city with hostile intentions he joined the fighting ranks and soon won Garibaldi's esteem by his bravery. Although wounded in the engagement of the 30th of April, he at once resumed his place in the ranks, but on the 3rd of June he was again wounded much more severely, and died in the Pellegrini hospital on the 6th of July 1849. Besides the poems mentioned above, he wrote hymns to Dante, to the Apostles, "Dio e popolo," &c. The chief merit of his work lies in the spontaneity and enthusiasm for the Italian cause which rendered it famous, in spite of certain technical imperfections, and he well deserved the epithet of "The Tyrtaeus of the Italian revolution."

See A. G. Barrili, "G. Mameli nella vita e nell' arte," in _Nuova
Antologia_ (June 1, 1902); the same writer's edition of the _Scritti
editi ed inediti di G. Mameli_ (Genoa, 1902); Countess Martinengo
Cesaresco, _Italian Characters_ (London, 1901); A. Luzio, _Profili
Biografici_ (Milan, 1906); G. Trevelyan, _Garibaldi's Defence of the
Roman Republic_ (London, 1907).

MAMELUKE (anglicized through the French, from the Arabic _mamluk_, a slave), the name given to a series of Egyptian sultans, originating (1250) in the usurpation of supreme power by the bodyguard of Turkish slaves first formed in Egypt under the successors of Saladin. See EGYPT: _History_ (Moslem period).

MAMERTINI, or "children of Mars," the name taken by a band of Campanian (or Samnite) freebooters who about 289 B.C. seized the Greek colony of Messana at the north-east corner of Sicily, after having been hired by Agathocles to defend it (Polyb. 1. 7. 2). The adventure is explained by tradition (e.g. Festus 158, Müller) as the outcome of a _ver sacrum_; the members of the expedition are said to have been the male children born in a particular spring of which the produce had been vowed to Apollo (cf. SAMNITES), and to have settled first in Sicily near Tauromenium. An inscription survives (R. S. Conway, _Italic Dialects_, 1) which shows that they took with them the Oscan language as it was spoken in Capua or Nola at that date, and the constitution usual in Italic towns of a free community (_touta_ =) governed by two annual magistrates (_meddices_). The inscription dedicated some large building (possibly a fortification) to Apollo, which so far confirms the tradition just noticed. Though in the Oscan language, the inscription is written in the Greek alphabet common to south Italy from the 4th century B.C. onwards, viz. the Tarentine Ionic, and so are the legends of two coins of much the same date as the inscription (Conway, ib. 4). From 282 onwards (B. V. Head, _Historia numorum_, 136) the legend itself is Graecized ([Greek: MAMERTINON] instead of [Greek: MAAMERTINOUM]) which shows how quickly here, as everywhere, "Graecia capta ferum victorem cepit." On the Roman conquest of Sicily the town secured an independence under treaty (Cicero, _Verr._ 3. 6. 13). The inhabitants were still called Mamertines in the time of Strabo (vi. 2. 3).

See further Mommsen, _C.I.L._ x. sub loc., and the references already
given. (R. S. C.)

MAMERTINUS, CLAUDIUS (4th century A.D.), one of the Latin panegyrists. After the death of Julian, by whom he was evidently regarded with special favour, he was praefect of Italy (365) under Valens and Valentinian, but was subsequently (368) deprived of his office for embezzlement. He was the author of an extant speech of thanks to Julian for raising him to the consulship, delivered on the 1st of January 362 at Constantinople. Two panegyrical addresses (also extant) to Maximian (emperor A.D. 286-305) are attributed to an older _magister_ Mamertinus, but it is probable that the corrupt MS. superscription contains the word _memoriae_, and that they are by an unknown _magister memoriae_ (an official whose duty consisted in communicating imperial rescripts and decisions to the public). The first of these was delivered on the birthday of Rome (April 21, 289), probably at Maximian's palace at Augusta Trevirorum (Trèves), the second in 290 or 291, on the birthday of the emperor. By some they are attributed to Eumenius (q.v.) who was a _magister memoriae_ and the author of at least one (if not more) panegyrics.

The three speeches will be found in E. Bahrens, _Panegyrici latini_ (1874); see also Teuffel-Schwabe, _Hist. of Roman Literature_ (Eng. trans.), § 417. 7.

MAMIANI DELLA ROVERE, TERENZIO, COUNT (1802-1885), Italian writer and statesman, was born at Pesaro in 1799. Taking part in the outbreaks at Bologna arising out of the accession of Pope Gregory XVI., he was elected deputy for Pesaro to the assembly, and subsequently appointed minister of the interior; but on the collapse of the revolutionary movement he was exiled. He returned to Italy after the amnesty of 1846, and in 1848 he was entrusted with the task of forming a ministry. He remained prime minister, however, only for a few months, his political views being anything but in harmony with those of the pope. He subsequently retired to Genoa where he worked for Italian unity, was elected deputy in 1856, and in 1860 became minister of education under Cavour. In 1863 he was made minister to Greece, and in 1865 to Switzerland, and later senator and councillor of state. Meanwhile, he had founded at Genoa in 1849 the Academy of Philosophy, and in 1855 had been appointed professor of the history of philosophy at Turin; and he published several volumes, not only on philosophical and social subjects, but of poetry, among them _Rinnovamente della filosofia antica italiana_ (1836), _Teoria della Religione e dello stato_ (1869), _Kant e l'ontologia_ (1879), _Religione dell' avenire_ (1880), _Di un nuovo diritto europeo_ (1843, 1857). He died at Rome on the 21st of May, 1885.

See _Indice delle opere di Terenzio Mamiani_ (Pesaro, 1887); Gaspare,
_Vita di Terenzio Mamiani_ (Ancona, 1887); Barzellotti, _Studii e
ritratti_ (Bologna, 1893).

MAMMALIA (from Lat. _mamma_, a teat or breast), the name proposed by the Swedish naturalist Linnaeus for one of the classes, or primary divisions, of vertebrated animals, the members of which are collectively characterized by the presence in the females of special glands secreting milk for the nourishment of the young. With the exception of the lowest group, such glands always communicate with the exterior by means of the teats, nipples or mammae, from which the class derives its name. The class-name (modified by the French into _Mammifères_, and replaced in German by the practically equivalent term _Säugethiere_) has been anglicized into "Mammals" (mammal, in the singular). Of recent years, and more especially in America, it has become a custom to designate the study of mammals by the term "mammalogy." Etymologically, however, that designation cannot be justified; for it is of hybrid (Latin and Greek) origin, and is equivalent to "mastology," the science which deals with the mammary gland (Gr. [Greek: mastos], woman's breast), a totally different signification. As regards existing forms of life, the limitations of the class are perfectly well defined and easy of recognition; for although certain groups (not, by the way, whales, which, although excluded in popular estimation from the class, are in all essential respects typical mammals) are exceedingly aberrant, and present structural features connecting them with the lower vertebrate classes, yet they are by common consent retained in the class to which they are obviously most nearly affiliated by their preponderating characteristics. There is thus at the present day a great interval, unbridged by any connecting links, between mammals and the other classes of vertebrates.

Not so, however, when the extinct forms of vertebrate life are taken into consideration, for there is a group of reptiles from the early part of the Secondary, or Mesozoic period, some of whose members must have been so intimately related to mammals that, were the whole group fully known, it would clearly be impossible to draw a distinction between Mammalia on the one hand and Reptilia on the other. Indeed, as it is, we are already partially acquainted with one of these early intermediate creatures (_Tritylodon_), which forms a kind of zoological shuttlecock, being, so to speak, hit from one group to another, and back again, by the various zoologists by whom its scanty remains have been studied. Considered collectively, mammals, which did not make their appearance on the earth for some time after reptiles had existed, are certainly the highest group of the whole vertebrate sub-kingdom. This expression must not, however, be considered in too restricted a sense. In mammals, as in other classes, there are low as well as high forms; but by any tests that can be applied, especially those based on the state of development of the central nervous system, it will be seen that the average exceeds that of any other class, that many species of this class far excel those of any other in perfection of structure, and that it contains one form which is unquestionably the culminating point amongst organized beings.

Mammals, then, are vertebrated animals, possessing the normal characteristics of the members of that primary division of the animal kingdom. They are separated from fishes and batrachians (Pisces and Batrachians) on the one hand, and agree with reptiles, and birds (Reptilia and Aves) on the other, in the possession during intra-uterine life of the membranous vascular structures respectively known as the amnion and the allantois, and likewise in the absence at this or any other period of external gills. A four-chambered heart, with a complete double circulation, and warm blood (less markedly so in the lowest group than in the rest of the class), distinguish mammals from existing reptiles, although not from birds. From both birds and reptiles the class is distinguished, so far at any rate as existing forms are concerned, by the following features: the absence of a nucleus in the red corpuscles of the blood, which are nearly always circular in outline; the free suspension of the lungs in a thoracic cavity, separated from the abdominal cavity by a muscular partition, or diaphragm, which is the chief agent in inflating the lungs in respiration; the aorta, or main artery, forming but a single arch after leaving the heart, which curves over the left terminal division of the windpipe, or bronchus; the presence of more or fewer hairs on the skin and the absence of feathers; the greater development of the bridge, or commissure, connecting the two halves of the brain, which usually forms a complete corpus callosum, or displays an unusually large size of its anterior portion; the presence of a fully developed larynx at the upper end of the trachea or windpipe, accompanied by the absence of a syrinx, or expansion, near the lower end of the same; the circumstance that each half of the lower jaw (except perhaps at a very early stage of development) consists of a single piece articulating posteriorly with the squamosal element of the skull without the intervention of a separate quadrate bone; the absence of prefrontal bones in the skull; the presence of a pair of lateral knobs, or condyles (in place of a single median one), on the occipital aspect of the skull for articulation with the first vertebra; and, lastly, the very obvious character of the female being provided with milk-glands, by the secretion of which the young (produced, except in the very lowest group, alive and not by means of externally hatched eggs) are nourished for some time after birth.

In the majority of mammals both pairs of limbs are well developed and adapted for walking or running. The fore-limbs may, however, be modified, as in moles, for burrowing, or, as in bats, for flight, or finally, as in whales and dolphins, for swimming, with the assumption in this latter instance of a flipper-like form and the complete disappearance of the hind-limbs. Special adaptations for climbing are exhibited by both pairs of limbs in opossums, and for hanging to boughs in sloths. In no instance are the fore-limbs wanting.

In the great majority of mammals the hind extremity of the axis of the body is prolonged into a tail. Very generally the tail has distinctly the appearance of an appendage, but in some of the lower mammals, such as the thylacine among marsupials, and the aard-vark or ant-bear among the edentates, it is much thickened at the root, and passes insensibly into the body, after the fashion common among reptiles. As regards function, the tail may be a mere pendent appendage, or may be adapted to grasp boughs in climbing, or even to collect food or materials for a nest or sleeping place, as in the spider-monkeys, opossums and rat-kangaroos. Among jumping animals it may serve as a balance, as in the case of jerboas and kangaroos, while in the latter it is also used as a support when resting; among many hoofed mammals it is used as a fly-whisk; and in whales and dolphins, as well as in the African _Potamogale_ and the North American musquash, it plays an important part in swimming. Its supposed use as a trowel by the beaver is, however, not supported by the actual facts of the case.

As already indicated, the limbs of different mammals are specially modified for various modes of life; and in many cases analogous modifications occur, in greater or less degree, throughout the entire body. Those modifications most noticeable in the case of cursorial types may be briefly mentioned as examples. In this case, as might be expected, the greatest modifications occur in the limbs, but correlated with this is also an elongation of the head and neck in long-legged types. Adaptation for speed is further exhibited in the moulding of the shape of the body so as to present the minimum amount of resistance to the air, as well as in increase in heart and lung capacity to meet the extra expenditure of energy. Finally, in the jumping forms we meet with an increase in the length and weight of the tail, which has to act as a counterpoise. As regards the feet, a reduction in the number of digits from the typical five is a frequent feature, more especially among the hoofed mammals, where the culmination in this respect is attained by the existing members of the horse tribe and certain representatives of the extinct South American _Proterotheriidae_, both of which are monodactyle. Brief reference may also be made to the morphological importance of extraordinary length or shortness in the skulls of mammals--dolichocephalism and brachycephalism; both these features being apparently characteristic of specialized types, the former condition being (as in the horse) often, although not invariably, connected with length of limb and neck, and adaptation to speed, while brachycephalism may be correlated with short limbs and an abbreviated neck. Exceptions to this rule, as exemplified by the cats, are due to special adaptive causes. In point of bodily size mammals present a greater range of variation than is exhibited by any other living terrestrial animals, the extremes in this respect being displayed by the African elephant on the one hand and certain species of shrew-mice (whose head and body scarcely exceed an inch and a half in length) on the other. When the aquatic members of the class are taken into consideration, the maximum dimensions are vastly greater, Sibbald's rorqual attaining a length of fully 80 ft., and being probably the bulkiest and heaviest animal that has ever existed. Within the limits of individual groups, it may be accepted as a general rule that increase in bulk or stature implies increased specialization; and, further, that the largest representatives of any particular group are also approximately the latest. The latter dictum must not, however, be pushed to an extreme, since the African elephant, which is the largest living land mammal, attaining in exceptional cases a height approaching 12 ft., was largely exceeded in this respect by an extinct Indian species, whose height has been estimated at between 15 and 16 ft.

In regard to sense-organs, ophthalmoscopic observations on the eyes of living mammals (other than man) have revealed the existence of great variation in the arrangement of the blood-vessels, as well as in the colour of the retina; blue and violet seem to be unknown, while red, yellow and green form the predominating shades. In the main, the various types of minute ocular structure correspond very closely to the different groups into which mammals are divided, this correspondence affording important testimony in the favour of the general correctness of the classification. Among the exceptions are the South American squirrel-monkeys, whose eyes approximate in structure to those of the lemurs. Man and monkeys alone possess parallel and convergent vision of the two eyes, while a divergent, and consequently a very widely extended, vision is a prerogative of the lower mammals; squirrels, for instance, and probably also hares and rabbits, being able to see an object approaching them directly from behind without turning their heads.

An osteological question which has been much discussed is the fate of the reptilian quadrate bone in the mammalian skull. In the opinion of F. W. Thyng, who has carefully reviewed all the other theories, the balance of evidence tends to show that the quadrate has been taken up into the inner ear, where it is represented among the auditory ossicles by the incus.

Although the present article does not discuss mammalian osteology in general (for which see VERTEBRATA), it is interesting to notice in this connexion that the primitive condition of the mammalian tympanum apparently consisted merely of a small and incomplete bony ring, with, at most, an imperfect ventral wall to the tympanic cavity, and that a close approximation to this original condition still persists in the monotremes, especially _Ornithorhynchus_. The tympano-hyal is the characteristic mammalian element in this region; but the entotympanic likewise appears to be peculiar to the class, and to be unrepresented among the lower vertebrates. The tympanum itself has been regarded as representing one of the elements--probably the supra-angular--of the compound reptilian lower jaw. The presence of only seven vertebrae in the neck is a very constant feature among mammals; the exceptions being very few.

Two other points in connexion with mammalian osteology may be noticed. A large number of mammals possess a perforation, or foramen, on the inner side of the lower end of the humerus, and also a projection on the shaft of the femur known as the third trochanter. From its occurrence in so many of the lower vertebrates, the entepicondylar foramen of the humerus, as it is called, is regarded by Dr E. Stromer as a primitive structure, of which the original object was to protect certain nerves and blood-vessels. It is remarkable that it should persist in the spectacled bear of the Andes, although it has disappeared in all other living members of the group. The third trochanter of the femur, on the other hand, can scarcely be regarded as primitive, seeing that it is absent in several of the lower groups of mammals. Neither can its presence be attributed, as Professor A. Gaudry suggests, to the reduction in the number of the toes, as otherwise it should not be found in the rhinoceros. Its general absence in man forbids the idea of its having any connexion with the upright posture.

_Hair._--In the greater number of mammals the skin is more or less
densely clothed with a peculiarly modified form of epidermis known as
hair. This consists of hard, elongated, slender, cylindrical or
tapering, thread-like masses of epidermic tissue, each of which grows,
without branching, from a short prominence, or papilla, sunk at the
bottom of a pit, or follicle, in the true skin, or dermis. Such hairs,
either upon different parts of the skin of the same species, or in
different species, assume very diverse forms and are of various sizes
and degrees of rigidity--as seen in the fur of the mole, the bristles
of the pig, and the spines of the hedgehog and porcupine, which are
all modifications of the same structures. These differences arise
mainly from the different arrangement of the constituent elements into
which the epidermal cells are modified. Each hair is composed usually
of a cellular pithy internal portion, containing much air, and a
denser or more horny external or cortical part. In some mammals, as
deer, the substance of the hair is almost entirely composed of the
central medullary or cellular substance, and is consequently very
easily broken; in others the horny part prevails almost exclusively,
as in the bristles of the wild boar. In the three-toed sloth
(_Bradypus_) the hairs have a central horny axis and a pithy exterior.
Though generally nearly smooth, or but slightly scaly, the surface of
some hairs is imbricated; that is to say, shows projecting scale-like
processes, as in some bats, while in the two-toed sloth (_Choloepus_)
they are longitudinally grooved or fluted. Though usually more or less
cylindrical or circular in section, hairs are often elliptical or
flattened, as in the curly-haired races of men, the terminal portion
of the hair of moles and shrews, and conspicuously in the spines of
the spiny squirrels of the genus _Xerus_ and those of the mouse-like
_Platacanthomys_. Hair having a property of mutual cohesion or
"felting," which depends upon a roughened scaly surface and a tendency
to curl, as in domestic sheep, is called "wool."

It has been shown by J. C. H. de Meijere that the insertion of the
individual hairs in the skin displays a definite arrangement, constant
for each species, but varying in different groups. In jerboas, for
example, a bunch of twelve or thirteen hairs springs from the same
point, while in the polar bear a single stout hair and several slender
ones arise together, and in the marmosets three equal-sized hairs form
regular groups. These tufts or groups likewise display an orderly and
definite grouping in different mammals, which suggests the origin of
such groups from the existence in primitive mammals of a scaly coat
comparable to that of reptiles, and indeed directly inherited
therefrom.

In a large proportion of mammals there exist hairs of two distinct
types: the one long, stiff, and alone appearing on the surface, and
the other shorter, finer and softer, constituting the under-fur, which
may be compared to the down of birds. A well-known example is
furnished by the fur-bearing seals, in which the outer fur is removed
in the manufacture of commercial "seal-skin," leaving only the soft
and fine under-fur.

Remarkable differences in the direction or slope of the hair are
noticeable on different parts of the body and limbs of many mammals,
especially in certain apes, where the hair of the fore-limbs is
inclined towards the elbow from above and from below. More remarkable
still is the fact that the direction of the slope often differs in
closely allied groups, as, for instance, in African and Asiatic
buffaloes, in which the hair of the middle line of the back has
opposite directions. Whorls of hair, as on the face of the horse and
the South American deer known as brockets, occur where the different
hair-slopes meet. In this connexion reference may be made to patches
or lines of long and generally white hairs situated on the back of
certain ruminants, which are capable of erection during periods of
excitement, and serve, apparently, as "flags" to guide the members of
a herd in flight. Such are the white chrysanthemum-like patches on the
rump of the Japanese deer and of the American prong-buck
(_Antilocapra_), and the line of hairs situated in a groove on the
loins of the African spring-buck. The white underside of the tail of
the rabbit and the yellow rump-patch of many deer are analogous.

The eye-lashes, or _ciliae_, are familiar examples of a special local
development of hair. Special tufts of stout stiff hairs, sometimes
termed _vibrissae_, and connected with nerves, and in certain cases
with glands, occur in various regions. They are most common on the
head, while they constitute the "whiskers," or "feelers," of the cats
and many rodents. In other instances, notably in the lemurs, but also
in certain carnivora, rodents and marsupials, they occupy a position
on the fore-arm near the wrist, in connexion with glands, and receive
sensory powers from the radial nerve. In some mammals the hairy
covering is partial and limited to particular regions; in others, as
the hippopotamus and the sea-cows, or Sirenia, though scattered over
the whole surface, it is extremely short and scanty; but in none is
it reduced to so great an extent as in the Cetacea, in which it is
limited to a few small bristles confined to the neighbourhood of the
lips and nostrils, and often present only in the young, or even the
foetal condition.

Some kinds of hairs, as those of the mane and tail of the horse,
persist throughout life, but more generally, as in the case of the
body-hair of the same animal, they are shed and renewed periodically,
generally annually. Many mammals have a longer hairy coat in winter,
which is shed as summer comes on; and some few, which inhabit
countries covered in winter with snow, as the Arctic fox, variable
hare and ermine, undergo a complete change of colour in the two
seasons, being white in winter and grey or brown in summer. There has
been much discussion as to whether this winter whitening is due to a
change in the colour of the individual hairs or to a change of coat.
It has, however, been demonstrated that the senile whitening of human
hair is due to the presence of phagocytes, which devour the
pigment-bodies; and from microscopic observations recently made by the
French naturalist Dr E. Trouessart, it appears that much the same kind
of action takes place in the hairs of mammals that turn white in
winter. Cold, by some means or other, causes the pigment-bodies to
shift from the normal positions, and to transfer themselves to other
layers of the hair, where they are attacked and devoured by
phagocytes. The winter whitening of mammals is, therefore, precisely
similar to the senile bleaching of human hair, no shift of the coat
taking place. Under the influence of exposure to intense cold a small
mammal has been observed to turn white in a single night, just as the
human hair has been known to blanch suddenly under the influence of
intense emotion, and in both cases extreme activity of the phagocytes
is apparently the inducing cause. The African golden-moles
(_Chrysochloris_), the desmans or water-moles (_Myogale_), and the
West African _Potamogale velox_, are remarkable as being the only
mammals whose hair reflects those iridescent tints so common in the
feathers of tropical birds.

The principal and most obvious purpose of the hairy covering is to
protect the skin. Its function in the hairless Cetacea is discharged
by the specially modified and thickened layer of fatty tissue beneath
the skin known as "blubber."

_Scales, &c._--True scales, or flat imbricated plates of horny
material, covering the greater part of the body, are found in one
family only of mammals, the pangolins or _Manidae_; but these are also
associated with hairs growing from the intervals between the scales or
on the parts of the skin not covered by them. Similarly imbricated
epidermic productions form the covering of the under-surface of the
tail of the African flying rodents of the family _Anomaluridae_; and
flat scutes, with the edges in apposition, and not overlaid, clothe
both surfaces of the tail of the beaver, rats and certain other
members of the rodent order, and also of some insectivora and
marsupials. Armadillos alone possess an external bony skeleton,
composed of plates of bony tissue, developed in the skin and covered
with scutes of horny epidermis. Other epidermic appendages are the
horns of ruminants and rhinoceroses--the former being elongated,
tapering, hollow caps of hardened epidermis of fibrous structure,
fitting on and growing from conical projections of the frontal bones
and always arranged in pairs, while the latter are of similar
structure, but without any internal bony support, and situated in the
middle line. Callosities, or bare patches covered with hardened and
thickened epidermis, are found on the buttocks of many apes, the
breast of camels, the inner side of the limbs of _Equidae_, the
grasping under-surface of the tail of prehensile-tailed monkeys,
opossums, &c. The greater part of the skin of the one-horned Asiatic
rhinoceros is immensely thickened and stiffened by an increase of the
tissue of both the skin and epidermis, constituting the well-known
jointed "armour-plated" hide of those animals.

_Nails, Claws and Hoofs._--With few exceptions, the terminal
extremities of the digits of both limbs of mammals are more or less
protected or armed by epidermic plates or sheaths, constituting the
various forms of nails, claws or hoofs. These are absent in the
Cetacea alone. A perforated spur, with a special secreting gland in
connexion with it, is found attached to each hind-leg of the males of
the existing species of Monotremata.

_Scent-glands, &c._--Besides the universally distributed sweat-glands
connected with the hair-system, most mammals have special glands in
modified portions of the skin, often involuted to form a shallow
recess or a deep sac with a narrow opening, situated in various parts
of the surface of the body, and secreting odorous substances, by the
aid of which individuals recognize one another. These probably afford
the principal means by which wild animals are able to become aware of
the presence of other members of the species, even at great distances.

To this group of structures belong the suborbital face-gland,
"larmier," or "crumen," of antelopes and deer, the frontal gland of
the muntjak and of bats of the genus _Phyllorhina_, the chin-gland of
the chevrotains and of _Taphozous_ and certain other bats, the
glandular patch behind the ear of the chamois and the reed-buck, the
glands on the lower parts of the legs of most deer and a few antelopes
(the position of which is indicated by tufts of long and often
specially coloured hair), the interdigital foot-glands of goats,
sheep, and many other ruminants, the temporal gland of elephants, the
lateral glands of the musk-shrew, the gland on the back of the hyrax
and the peccary (from the presence of which the latter animal takes
the name _Dicotyles_), the gland on the tails of the members of the
dog-tribe, the preputial glands of the musk-deer and beaver (both well
known for the use made of their powerfully odorous secretion in
perfumery), and also of the swine and hare, the anal glands of
Carnivora, the perineal gland of the civet (also of commercial value),
the caudal glands of the fox and goat, the gland on the wing-membrane
of bats of the genus _Saccopteryx_, the post-digital gland of the
rhinoceros, &c. Very generally these glands are common to both sexes,
and it is in such cases that their function as a means of mutual
recognition is most evident. It has been suggested that the
above-mentioned callosities or "chestnuts" on the limbs of horses are
vestigial scent-glands; and it is noteworthy that scrapings or
shavings from their surface have a powerful attraction for other
horses, and are also used by poachers and burglars to keep dogs
silent. The position of such glands on the lower portions of the limbs
is plainly favourable to a recognition-taint being left in the tracks
of terrestrial animals; and antelopes have been observed deliberately
to rub the secretion from their face-glands on tree-trunks. When
glands are confined to the male, their function is no doubt sexual;
the secretion forming part of the attraction, or stimulus, to the
other sex.

_Dentition._--In the great majority of mammals the teeth form a
definite series, of which the hinder elements are of a more or less
complex type, while those in front are simpler. With the exception of
the marsupials, a set of deciduous, or milk, teeth is developed in
most mammals with a complicated type of dentition; these milk-teeth
being shed at a comparatively early period (occasionally even _in
utero_), when they are succeeded by the larger permanent series, which
is the only other ever developed. This double series of teeth thus
forms a very characteristic feature of mammals generally. Both the
milk and the permanent dentition display the aforesaid complexity of
the hinder teeth as compared with those in front, and since the number
of milk-teeth is always considerably less than that of the permanent
set, it follows that the hinder milk-teeth are usually more complex
than the teeth of which they are the predecessors in the permanent
series, and represent functionally, not their immediate successors,
but those more posterior permanent teeth which have no direct
predecessors. This character is clearly seen in those animals in which
the various members of the lateral or cheek series are well
differentiated from each other in form, as the Carnivora, and also in
man.

In mammals with two sets of teeth the number of those of the permanent
series preceded by milk-teeth varies greatly, being sometimes, as in
marsupials and some rodents, as few as one on each side of each jaw,
and in other cases including the larger portion of the series. As a
rule, the teeth of the two sides of the jaws are alike in number and
character, except in cases of accidental or abnormal variation, and in
the tusks of the narwhal, in which the left is of immense size, and
the right rudimentary. In mammals, such as dolphins and some
armadillos, which have a large series of similar teeth, not always
constant in number in different individuals, there may indeed be
differences in the two sides; but, apart from these in describing the
dentition of any mammal, it is generally sufficient to give the number
and characters of the teeth of one side only. As the teeth of the
upper and the lower jaws work against each other in masticating, there
is a general correspondence or harmony between them, the projections
of one series, when the mouth is closed, fitting into corresponding
depressions of the other. There is also a general resemblance in the
number, characters and mode of succession of both series; so that,
although individual teeth of the upper and lower jaws may not be in
the strict sense of the term homologous parts, there is a great
convenience in applying the same descriptive terms to the one which
are used for the other.

The simplest dentition is that of many species of dolphin (fig. 1), in
which the crowns are single-pointed, slightly curved cones, and the
roots also single and tapering; so that all the teeth are alike in
form from the anterior to the posterior end of the series, though it
may be with some slight difference in size, those at the two
extremities being rather smaller than the others. Such a dentition is
called "homoeodont" (Gr. [Greek: homoios], like, [Greek: odous],
tooth), and in the case cited, as the teeth are never changed, it is
also monophyodont (Gr. [Greek: monos], alone, single, [Greek: phyein],
to generate, [Greek: odous], tooth). Such teeth are adapted only for
catching slippery living prey, like fish.

In a very large number of mammals the teeth of different parts of the
series are more or less differentiated in character; and, accordingly,
have different functions to perform. The front teeth are simple and
one-rooted, and are adapted for cutting and seizing. They are called
"incisors." The back, lateral or cheek teeth, on the other hand, have
broader and more complex crowns, tuberculated or ridged, and supported
on two or more roots. They crush or grind the food, and are hence
called "molars." Many mammals have, between these two sets, a tooth at
each corner of the mouth, longer and more pointed than the others,
adapted for tearing or stabbing, or for fixing struggling prey. From
the conspicuous development of such teeth in the Carnivora, especially
the dogs, they have received the name of "canines." A dentition with
its component parts so differently formed that these distinctive terms
are applicable to them is called heterodont (Gr. [Greek: heteros],
different). In most cases, though by no means invariably, mammals with
a heterodont dentition are also diphyodont (Gr. [Greek: diphyês], of
double form).

This general arrangement is obvious in a considerable number of
mammals; and examination shows that, under great modifications in
detail, there is a remarkable uniformity of essential characters in
the dentition of a large number of members of the class belonging to
different orders and not otherwise closely allied, so much that it is
possible to formulate a common plan of dentition from which the others
have been derived by the alteration of some and the suppression of
other members of the series, and occasionally, but very rarely, by
addition. In this generalized form of mammalian dentition the total
number of teeth present is 44, or 11 above and 11 below on each side.
Those of each jaw are placed in continuous series without intervals
between them; and, although the anterior teeth are simple and
single-rooted, and the posterior teeth complex and with several roots,
the transition between the two kinds is gradual.

In dividing and grouping such teeth for the purpose of description and
comparison more definite characters are required than those derived
merely from form or function. The first step towards a classification
rests on the fact that the upper jaw is composed of two bones, the
premaxilla and the maxilla, and that the division or suture between
these bones separates the three front teeth from the rest. These three
teeth, which are implanted in the premaxilla, form a distinct group,
to which the name of "incisor" is applied. This distinction is,
however, not so important as it appears at first sight, for their
connexion with the bone is only of a secondary nature, and, although
it happens conveniently that in the great majority of cases the
division between the bones coincides with the interspace between the
third and fourth tooth of the series, still, when it does not, as in
the mole, too much weight must not be given to this fact, if it
contravenes other reasons for determining the homologies of the teeth.
The eight remaining teeth of the upper jaw offer a natural division,
inasmuch as the three hindmost never have milk-predecessors; and,
although some of the anterior teeth may be in the same case, the
particular one preceding these three always has such a predecessor.
These three, then, are grouped as the "molars." Of the five teeth
between the incisors and molars the most anterior, or the one usually
situated close behind the pre-maxillary suture, very generally assumes
a lengthened and pointed form, and constitutes the "canine" of the
Carnivora, the tusk of the boar, &c. It is customary, therefore, to
call this tooth, whatever its size or form, the "canine." The
remaining four are the "premolars." This system has been objected to
as artificial, and in many cases not descriptive, the distinction
between premolars and canine especially being sometimes not obvious;
but the terms are now in such general use, and also so convenient,
that it is not likely they will be superseded. It is frequently
convenient to refer to all the teeth behind the canine as the
"cheek-teeth."

With regard to the lower teeth the difficulties are greater, owing to
the absence of any suture corresponding to that which defines the
incisors above; but since the number of the teeth is the same, since
the corresponding teeth are preceded by milk-teeth, and since in the
large majority of cases it is the fourth tooth of the series which is
modified in the same way as the canine (or fourth tooth) of the upper
jaw, it is reasonable to adopt the same divisions as with the upper
series, and to call the first three, which are implanted in the part
of the mandible opposite to the premaxilla, the incisors, the next the
canine, the next four the premolars, and the last three the molars.

It may be observed that when the mouth is closed, especially when the
opposed surfaces of the teeth present an irregular outline, the
corresponding upper and lower teeth are not exactly opposite,
otherwise the two series could not fit into one another, but as a rule
the points of the lower teeth shut into the interspaces in front of
the corresponding teeth of the upper jaw. This is very distinct in the
canine teeth of the Carnivora, and is a useful guide in determining
the homologies of the teeth of the two jaws.

For the sake of brevity the complete dentition is described by the
following formula, the numbers above the line representing the teeth
of the upper, those below the line those of the lower jaw: incisors
(3--3)/(3--3), canines (1--1)/(1--1), premolars (4--4)/(4--4), molars,
(3--3)/(3--3) = (11--11)/(11--11) total 44. As, however, initial
letters may be substituted for the names of each group, and it is
unnecessary to give more than the numbers of the teeth on one side of
the mouth, the formula may be abbreviated into:

_i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 3/3; total 44.

The individual teeth of each group are enumerated from before
backwards, and by such a formula as the following:--

_i_ 1, _i_ 2, _i_ 3, _c_, _p_ 1, _p_ 2, _p_ 3, _p_ 4, _m_ 1, _m_ 2, _m_ 3
-------------------------------------------------------------------------
_i_ 1, _i_ 2, _i_ 3, _c_, _p_ 1, _p_ 2, _p_ 3, _p_ 4, _m_ 1, _m_ 2, _m_ 3

a special numerical designation is given by which each one can be
indicated. In mentioning any single tooth, such a sign as m1 will mean
the first upper molar, m1 the first lower molar, and so on.

When, as is the case among nearly all existing mammals with the
exception of the members of the genera _Sus_ (pigs), _Gymnura_
(rat-shrew), _Talpa_ (moles) and _Myogale_ (desmans) the number of
teeth is reduced below the typical forty-four, it appears to be an
almost universal rule that if one of the incisors is missing it is the
second, or middle one, while the premolars commence to disappear from
the front end of the series and the molars from the hinder end.

The milk-dentition is expressed by a similar formula, _d_ for
deciduous, being added before the letter expressive of the nature of
the tooth. As the three molars and (almost invariably) the first
premolar of the permanent series have no predecessors, the typical
milk-dentition would be expressed as follows: _di_ 3/3, _dc_ 1/1, _dm_
3/3 = 28. The teeth which precede the premolars of the permanent
series are called either milk-molar or milk-premolar. When there is a
marked difference between the premolars and molars of the permanent
dentition, the first milk-molar resembles a premolar, while the last
has the characters of the posterior molar. It is sometimes convenient
to refer to all the seven cheek-teeth as members of a single
continuous series (which they undoubtedly are), and for this purpose
the following nomenclature has been proposed:--

Upper Jaw. Lower Jaw.
Cheek-tooth 1 Protus. Protid.
" 2 Deuterus. Deuterid.
" 3 Tritus. Tritid.
" 4 Tetartus. Tetartid.
" 5 Pemptus. Pemptid.
" 6 Hectus. Hectid.
" 7 Hebdomus. Hebdomid.

With the exception of the Cetacea, most of the Edentata, and the
Sirenia, in which the teeth, when present, have been specialized in a
retrograde or aberrant manner, the placental mammals as a whole have a
dentition conforming more or less closely to the foregoing type.

With the marsupials the case is, however, somewhat different; the
whole number not being limited to 44, owing largely to the fact that
the number of upper incisors may exceed three pairs, reaching indeed
in some instances to as many as five. Moreover, with the exception of
the wombats, the number of pairs of incisors in the upper always
exceeds those in the lower. When fully developed, the number of
cheek-teeth is, however, seven; and it is probable that, as in
placentals, the first four of these are premolars and the remaining
three molars, although it was long held that these numbers should be
transposed. The most remarkable feature about the marsupial dentition
is that, at most, only a single pair of teeth is replaced in each jaw;
this pair, on the assumption that there are four premolars,
representing the third of that series. With the exception of this
replacing pair of teeth in each jaw, it is considered by many
authorities that the marsupial dentition corresponds to the deciduous,
or milk, dentition of placentals. If this be really the case, the
rudiments of an earlier set of teeth which have been detected in the
jaws of some members of the order, represent, not the milk-series, but
a prelacteal dentition. On the assumption that these functional teeth
correspond to the milk-series of placentals, marsupials in this
respect agree exactly with modern elephants, in which the same
peculiarity exists.

In very few mammals are teeth entirely absent. Even in the whalebone
whales their germs are formed in the same manner and at the same
period of life as in other mammals, and even become partially
calcified, although they never rise above the gums, and completely
disappear before birth. In the American anteaters and the pangolins
among the Edentata no traces of teeth have been found at any age.
Adult monotremes are in like case, although the duck-billed platypus
(_Ornithorhynchus_) has teeth when young on the sides of the jaws. The
northern sea-cow (_Rhytina_), now extinct, appears to have been
toothless throughout life.

In different groups of mammals the dentition is variously specialized
in accordance with the nature of the food on which the members of
these groups subsist. From this point of view the various adaptive
modifications of mammalian dentition may be roughly grouped under the
headings of piscivorous, carnivorous, insectivorous, omnivorous and
herbivorous.

The fish-eating, or piscivorous, type of dentition is exemplified
under two phases in the dolphins and in the seals (being in the latter
instance a kind of retrograde modification from the carnivorous type).
In the dolphins, and in a somewhat less marked degree among the seals,
this type of dentition consists of an extensive series of conical,
nearly equal-sized, sharp-pointed teeth, implanted in an elongated and
rather narrow mouth (fig. 1), and adapted to seize slippery prey
without either tearing or masticating. In the dolphins the teeth form
simple cones, but in the seals they are often trident-like; while in
the otters the dentition differs but little from the ordinary
carnivorous type.

This carnivorous adaptation, in which the function is to hold and kill
struggling animals, often of large size, attains its highest
development in the cats (_Felidae_). The canines are in consequence
greatly developed, of a cutting and piercing type, and from their wide
separation in the mouth give a firm hold; the jaws being as short as
is consistent with the free action of the canines, or tusks, so that
no power is lost. The incisors are small, so as not to interfere with
the penetrating action of the tusks; and the crowns of some of the
teeth of the cheek-series are modified into scissor-like blades, in
order to rasp off the flesh from the bones, or to crack the bones
themselves, while the later teeth of this series tend to disappear.

In the insectivorous type, as exemplified in moles and shrew-mice, the
middle pair of incisors in each jaw are long and pointed so as to have
a forceps-like action for seizing insects, the hard coats of which are
broken up by the numerous sharp cusps surmounting the cheek-teeth.

In the omnivorous type, as exemplified in man and monkeys, and to a
less specialized degree in swine, the incisors are of moderate and
nearly equal size; the canines, if enlarged, serve for other purposes
than holding prey, and such enlargement is usually confined to those
of the males; while the cheek-teeth have broad flattened crowns
surmounted by rounded bosses, or tubercles.

In the herbivorous modification, as seen in three distinct phases in
the horse, the kangaroo, and in ruminants, the incisors are generally
well developed in one or both jaws, and have a nipping action, either
against one another or against a toothless hard pad in the upper jaw;
while the canines are usually small or absent, at least in the upper
jaw, but in the lower jaw may be approximated and assimilated to the
incisors. The cheek-teeth are large, with broad flattened crowns
surmounted either by simple transverse ridges, or complicated by
elevations and infoldings. In the specialized forms the premolars tend
to become more or less completely like the molars; and, contrary to
what obtains among the Carnivora, the whole series of cheek-teeth
(with the occasional exception of the first) is very strongly
developed.

Opinions differ as to the mode in which the more complicated
cheek-teeth of mammals have been evolved from a simpler type of tooth.
According to one theory, this has been brought about by the fusion of
two or more teeth of a simple conical type to form a compound tooth. A
more generally accepted view--especially among palaeontologists--is
the tritubercular theory, according to which the most generalized type
of tooth consists of three cusps arranged in a triangle, with the apex
pointing inwards in the teeth of the upper jaw. Additions of extra
cusps form teeth of a more complicated type. Each cusp of the
primitive triangle has received a separate name, both in the teeth of
the upper and of the lower jaw, while names have also been assigned to
super-added cusps. Molar teeth of the simple tritubercular type
persist in the golden moles (_Chrysochloris_) among the Insectivora
and also in the marsupial mole (_Notoryctes_) among the marsupials.
The type is, moreover, common among the mammals of the early Eocene,
and still more so in those of the Jurassic epoch; this forming one of
the strongest arguments in favour of the tritubercular theory. (See
Professor H. F. Osborn, "Palaeontological Evidence for the Original
Tritubercular Theory," in vol. xvii. (new series) of the _American
Journal of Science_, 1904.)