are much larger than the one or two lateral which may be present.

The PHASCOLOMYID.E are the rodents of the marsupials with one chisel-
like incisor in each half of each ja\v. Phascalomys, wombat. The MACRO-



63J:



CHORD AT A.



PODID.E, or kangaroos, resemble the ungulates in their large herds on the
grassy places. The fore legs being very small, the animals leap with the
strong hind legs and tail. Macropus giganteus. The PHALANGISTID.E
have very variable teeth. They resemble in habits the squirrels, Petaurus
having the same parachute folds as does our flying squirrel. The Dipro-
todonta contain many fossil forms in Australia and a few in South
America. Some of the Australian fossils were very large, Diprotodon
australis larger than a rhinoceros.

Sub. Class III. Placentalia (Monodelpliia).

The first reason for associating the mammals of the Old World
and most of those of the New together as Placentalia is an embry-
ological one, the presence of a placenta. When serosa, amnion,
and allantois (p, 553) have developed in the embryo, the vessels
of the allantois spread out beneath the serosa and form with this
the chorion, which sends small processes or villi into the now

highly vascular mucous mem-
brane of the uterus in order to
obtain nourishment somewhat as
a tree obtains food by its roots.
These villi may be distributed
over the greater part of the sur-
face (fig. 658), producing the
chorion frondosum, or diffuse
placenta, which occurs in Cetacea,
perissodactyles and many artio-
dactyles (swine). On the other
hand the vilH may be restricted
to certain places, becoming very

FIG. 658. Diagram of mammalian em- . ., _,,, .

biTO with chorion frondosum;afo,amni- Strong there. JLhlS glVCS rise to
otic cavity; aZ, allantois; am, amnion; , -i j -> -j i

as, umbilical cord; c/i, chorion; c/,z, cotyledonary, discoidal, or zonary

chorion ic villi ; dg, yolk stalk ; ds, yolk -, m , -i T

sac ; r, space (extra-embryonic coelom), placentae, lo these Correspond
between chorion and ammon;*, serosa. porti(mg rf ^ ^^ ];ning

which are distinguished from the rest by becoming extremely vas-
cular (uterine placenta). The cotyledonary placenta (fig. 659)
consists of many small placentar patches, the cotyledons (most
ruminants). In the zonary placenta the villous area takes the
shape of a girdle or barrel (carnivores, Sirenia), while the discoidal
(other mammals) is, as its name indicates, disc-like.

Besides the placental structures the higher mammals are char-
acterized by the disappearance of the cloaca, the unpaired vagina,
and absence of marsupial bones and inflected angle of the jaw. The




eh



IV. VERTEBRATA: MAMMALIA, EDENTATA. 635

dentition, on the other hand, has undergone a progressive, diver-
gent development, so that the distinctions are much more pro-
nounced than in the marsupials, and hence of importance in
differentiating the orders.

Order I. Edentata.

A few families, poor in species, are united under the name
Edentata because teeth are absent or, as is more usually the case,
are markedly degenerate. Persistent functional incisors are lack-




FIG. 659. Cotyledonary placenta and embryo of cow. (From Balfour, after Colin.)
C 1 , cotyledons of uterine, C 2 , of foetal placenta; Ch, chorion ; U, uterus; V,
vagina.

ing, canines but rarely occur (Brady pus)', molars may be present,
sometimes in great numbers (Priodongigas, the large armadillo, has
about a hundred molars), but they are poorly rooted, prismatic,
without enamel, and usually monophyodont. Since the aardvark
(Orycteropus) and Tatusia have a heterodont milk dentition in
embryonic life in which incisors occur, and fossil edentates
(Entelops) with complete dentition are known, the absence of a
replacement of the teeth is to be explained by degeneration, which
may affect other parts, and is to a certain extent the reason for the
low position accorded these forms. The great number of sacral
vertebrae is striking, being as many as thirteen in some armadillos.
The placenta is very variable, being diffuse, discoidal, or zonary in
different species. The group is essentially tropical, but one species



636 CHORDATA.

entering the United States. The oldest fossils occur in the Santa
Cruz beds of Patagonia (eocene or oligocene).

Sub Order I. NOMARTHRA. Old World edentates. FODIENTIA.
Animals with strong digging claws, long tail, and long, vermiform, sticky
tongue used in catching ants and other insects. Orycteropus capensis,
aardvark, with long snout, sparse bristly hair, five small molars, and
rudimentary milk dentition. SQUAMATA. Toothless, body covered with
overlapping scales. Manis, pangolins of Asia and Africa (fig. 660).




FIG. 660. Manis longicaiidata, pangolin. (From Monteiro.)

Sub Order II. XENARTHRA. Edentates of the New World. VER-
MILINGrUIA, ant eaters. Resemble manids in toothless jaws, long ant-
catching tongues, and strong digging claws, but are hairy and lack scales.
Myrmecophaga. TARDIG-RADA, sloths. Hairy, head short, rudimentary
tail, and few teeth, long strong claws by which they hang back down-
wards from limbs of trees. Bradypus tridactylus, nine cervical verte-
brae ; Cholcepus, six cervicals. Fossils allied are Megatherium, as large
as an elephant, Mylodon, Megalonyx, these two extending north to Penn-
sylvania. LORICATA, armadillos. Body with armor of bony plates,
molars numerous ; insectivorous. In the extinct GLYPTODONTID^E of South
America the plates fused to a continuous armor. One species twelve feet
long. One species may have occurred in Europe. DASYPODID.E ; dermal
armor in three or more movable transverse plates ; nocturnal. Genera
based upon the number of bands: Dasypus, Xenurus ; Tacusia novem-
cincta * enters United States.

Order II. Insectivora.

These primitive forms have a complete dentition, all the differ-
ent kinds of teeth being present, although they vary in number.
The roots are developed early and consequently the teeth are small.
Since they end with sharp cusps, adapted for eating insects, they
resemble the carnivores, from which they may be distinguished by



IV. VERTEBRATA: MAMMALIA, CHIROPTERA. 637




the rudimentary condition or occasional absence of the canines
(Talpa fjii. miny shrews ffff). There is great variability in
the matter of replacement of teeth; in the shrews, for instance,
the milk dentition is suppressed and
the second only is functional, while in
the hedgehog one incisor and one pre-
molar in each jaw, a second premolar
and the canine of the lower jaw func-
tion in both dentitions. In many re- FIG. 66i.-skuii of Sorex. (From

,, . ,. Ludwig-Leunis.)

spects the insectivores resemble the

rodents : a clavicle is present ; there are usually five toes furnished
with claws; there is a uterus bicornis, often divided its whole
length, and discoidal placenta.

Aside from the proboscis-like snout the insectivores resemble the
rodents in appearance, forming parallel groups to those of that order.
The ERINACID.E, or hedgehogs, of the Old World are spined like the porcu-
pines ; the SORICID.E, or shrews (Sorex,* Blarina*), are mouse-like, as are
the allied TALPID.E, or moles (Scalops,* Condylura,* star-nosed mole),
which burrow in the earth and have the eyes more or less rudimentary.
Some authors place here Galeopithecus of the East Indies, which has a
similar membrane and similar sailing powers as the flying squirrels. It
also presents resemblance to the bats and to the lemurs. The earliest
known insectivores date from the eocene.




FIG. 662. Skeleton of bat. (After Brehm.)

Order III. Chiroptera.

The bats are the only mammals which actually fly, and this at
once characterizes them. The flying membrane (patagium) is a
thin fold of skin, richly supplied with nerves, which begins at the



638 CHORDATA.

tail, includes the lower extremities to the foot, and extends thence
to the fingers, leaving the thumb free. Fingers 2-5 are enormously
elongated and support the membrane. Since flight requires
strong muscles, the sternum develops a small keel, recalling that
of birds, for the attachment of the large pectoral muscle. In con-
nexion with the flying powers the clavicle is strong. The patagium
is the seat of a very acute tactile sense, by means of which blinded
bats can fly among all kinds of obstacles without disturbing them.
The enormous ear conchs and a noticeable nose leaf, widely dis-
tributed through the group, also have marked tactile powers. In
the pectoral position of the mammary glands and in the discoidal
placenta these animals resemble the primates. In temperate
regions bats hibernate during the winter. The dentition is vari-
able, often fllf . Fossils occur in the eocene.

Sub Order I. MICROCHIROPTERA, with insectivorous dentition,
only the thumb of the fore limbs clawed. VESPERTILIONID^, tail long, no
nose leaf ; Vesperugo* Atalapha* PHYLLOSTOMID^E, with nose leaf, trop-
ical America ; Desmodus, the blood-sucking or vampyre bat.

Sub Order II. MACHROCHI ROPIER A (Frugivora), with smooth-
crowned molars, claws on thumb and first two fingers. Includes the flying
foxes, Pteropus, of the East Indies.

Order IV. Rodentia.

The rodents unite great similarity in appearance with a char-
acteristic dentition. The canines are absent, and the molars are
separated by a large gap (diastema) from the incisors (fig. 663).

The latter are strong, chisel-like,
have persistent pulps and grow at
the lower end as they are worn
away at the cutting edge. Since
only the front surface has enamel,
wear keeps them constantly sharp.
Usually there is but a single in-
cisor, and only in the Duplici-
dentata is a second present in the
upper jaw. The molars are cus-
FIG. 663. skull of porcupine. (From pidate or have enamel folds and

Schmarda.) /, frontal; im, premaxil- *

lary; k, temporal fossa continuous in frequently Continue to ffl'OW
front with orbit; o, infraorbital fora- J .

men, enormous on account of the por- throughout llie. Their number IS
tion of the masseter muscle which , , , , . , _

passes through it. frequently reduced, the formulae

varying between f - f | and -J-J-J-f. Many species have an inflected
angle of the jaw like that of marsupials. The infraorbital canal
is a striking feature in Muridae and Hystricidae (fig. 663, 0), a




IV. VERTEBRATA: MAMMALIA, UNGULATA. 639

large opening in front of the orbit in which a part of the masseter
muscle is attached.

The rodents are distinguished from the ungulates, which, like
them, are herbivorous, by the usually smaller size, the possession
of claws, five toes (sometimes reduced to three), the occurrence
usually of a clavicle, and a discoid placenta. The mammae are
inguinal in position and, corresponding to the great fertility, are
very numerous. The occurrence of glands with a strong-smelling
secretion, which open near the anus, is common. About nine
hundred living species are known, occurring in all regions except
the Australian. The order appears in the eocene.

Sub Order I. DUPLICIDENTATA (Lagomorpha), two upper incisors,
includes the hares, Lepus,* and the picas, Lagomys.*

Sub Order II. SCIUROMORPHA. The squirrels, SCIURID.E, are distin-
guished by the soft fur and bushy tail. Sciurus,* squirrels ; Cynomys,*
prairie dogs ; Sciuropterus,* flying squirrels. The CASTORID^E have soft fur
and scaly tail. Castor fiber * beaver of Europe and America.

Sub Order III. MYOMORPHA, rats and mice. Mus musculus,*
common mouse; Mus rattus,* house rat, once abundant but now replaced
by the gray rat, M. decumanus,* an immigrant from Asia. White rats are
albinos of M. rattus. Fiber zibethicus* musk rat; Arvieola* field mice.

Sub Order III. HYSTRICOMORPHA. The porcupines (HYSTRICID^E)
have spines; the Old World forms, Hystrix, are terrestrial, ours (Erethyzon)
arboreal. The CAVHD.E of South America have hoof-like claws. Cavia
cobaya, guinea pig. Hydrochosrtis, capybara, the largest existing rodent.

Order V. Ungulata.

Under the heading of Ungulata, or hoofed animals, are here
included two groups of living animals in which the body weight
is supported on hoofs on the tips of the toes, and which are sharply
marked off from other forms. If, however, the fossils are in-
cluded, the limits of the group must be extended so that it includes
the elephants and conies of the existing fauna as well as several
extinct forms, for these so interlock and intergrade that sharp
lines cannot be drawn.

The ungulates, which arise from common ancestors, the Oon-
dylarthra, the representatives of which occur in the eocene of
America (Phenacodon), are preeminently herbivorous; the canines
are rarely well developed, the molars numerous and adapted to
grinding the food, more or less flattened and frequently with
folded enamel. The mammae are inguinal, the uterus bicornuate,
and the placenta either diffuse or (most ruminants) cotyledonary
(fig. 659). The legs are exclusively locomotor structures and, to



640



CHORD ATA.



permit freer motion, the clavicles are absent ; the feet touch but
the tips of the toes, enclosed in hoofs, to the ground (unguligrade).
Since the metacarpals and metatarsals are greatly elongate, the
wrist and ankle are raised high from the ground so that they are
frequently confounded with elbow and knee. With this exclu-
sively supporting character of the limbs there is the same tendency
to reduction and fusion of bones which was noticed in birds (p.
606). There is a constant increase in the development of radius
and tibia to the chief supports of the body, the fibula becoming
rudimentary, the ulna being developed sometimes throughout its
whole extent, sometimes only in its upper part, which serves for the
attachment of muscles (olecranon), and is more or less fused with
the radius. The same tendency to simplification prevails in the
feet, but is expressed differently in the odd-toed (perissodactyle)
and even-toed (artiodactyle) forms. In the Perissodactyla the





\




FIG. 664. Fore feet of ungulates. (After Flower.) A-C, perissodactyle ; D-F, artio-
dactyle. A, tapir; R, rhinoceros; C, horse; D, pig; E, deer; F, camel, c, trique-
trum (ulnare); /, lunatum (intermedium); rn, capitatum; w 2 -w 5 , rudiments of
metacarpals II and V; p, pisiforme; R, radius; ,s, scaphoid (radiale); td, trapezoid;
tm, trapezium; U, ulna; w, hamatum; II- V, digits.

axis of pressure passes through the middle toe (fig. 664, AC,
III), while the other toes disappear symmetrically around this.
Since the first toe is early lost, toe V is next to disappear (J?), and
then toes II and IV (C), so that at last there remain only the
skeleton and hoof of the middle toe (horse), the rudiments of toes
II and IV persisting as the small splint bones.

In the Artiodactyla the axis of pressure falls between toes III
and IV (fig. 664, /)), which both unite in supporting the body
and are equally developed and frequently fuse, at least so far as
the metacarpals are concerned (E, F}. The figures D-F show



IV. VERTEBRATA: MAMMALIA, UNO UL AT A. 641

how the other digits disappear, digit I being lost still earlier.
Since the weight of the body rests more upon the hind legs than
upon the front ones, the former are the first to become modified.
Since we are able, by using abundant paleontological material, to
follow in detail the lines of descent of both artiodactyles and peris-
sodactyles, the conclusion is certain that these form diverging
series, distinct from the beginning. In each series most of the
common characters enumerated above have been independently
acquired so that the uniformity in appearance of the various
groups of ungulates is in great part the result of convergence.
The discussion of the fossils will be given under a separate head.

Sub Order I. PERISSODACTYLA (Solidungula). The dentition is
peculiar in having molars and premolars (with more or less pronounced
enamel folds) of equal size; a second character is the predominant devel-
opment of the middle toe, the others in the three existing families reduced
to different degrees. TAPIRID^E, fore feet four-toed, hind feet three-toed;
teeth i^||; nose elongate into a proboscis. Tapirus, tapirs, tropical Amer-
ica and India. RHINOCEROTIDJE, three toes on all feet, teeth ff; one or
two horns on the nasal bones, these without skeleton; skin thick, hairless,
hence these were formerly united with elephants as Pachydermata.
Rhinoceros, a single horn, India; Ceratorhmus (Asia), Atelodus (Africa),
have two horns. EQUID.E, a single functional toe, toes II and IV forming
splint bones (fig. 664, c); teeth |{|| ; Equus cdballus* horse, a native of
Asia; E. asinus, ass; E. zebra. Hybrids between jackass and mare are
called mules; between stallion and she-ass, hinnies.

Sub Order II. ARTIODACTYLA. Besides the features of the feet,
these forms have the premolars, three or four in number, smaller than the
molars. The species are much more numerous than the perissodactyles
and may be divided into three sections. Section I, NON-RUMINANTIA
(Bunodontia); omnivorous and have correspondingly a bunodont dentition,

Jj|, the canines frequently developed into tusks; the stomach is

usually simple, but is occasionally divided into three chambers (Dicotyles,
Hippopotamus), although rumination does not occur. The leg skeleton is
little modified (fig. 664, D), ulna and fibula not being reduced, and meta-
carpals and metatarsals separate. HIPPOPOTAMUS ; all four toes reach the
ground; skin thick (' pachyderm'), body heavy; living species all African.
Hippopotamus. SUID^E; two functional toes, skin with bristles, snout
proboscis-like. Sus scrofa, swine ; Dicotyles* peccaries of warmer
America.

Section II. RUMINANTIA (Pecora); teeth and stomach are adapted to
the exclusively herbivorous diet. The stomach (fig. 665) is divided into
two portions, each again subdivided. The first of these, the rumen, or
paunch (ru), receives the food as it is eaten; then at a time of quiet it is
regurgitated into the mouth and ground by the molars (' chewing the cud ').
It then passes back, this time into the second division, the honeycomb, or



642



CHORD AT A.



reticulum (re), thence to the many plies or omasum (o), and lastly to the
abomasum, or true stomach (a). Usually not only the canines but the in-
cisors of the upper jaw are degenerate, while the incisors of the lower jaw
are strong and the canines have taken the form and position of incisors.
The molars are seleriodont (have crescent-shaped cusps). With few excep-
tions they are of large size and many bear horns on the frontal bones. These
are larger in the males and may occur exclusively in that sex. In the sim-
plest case (giraffes) these are cones of horn free from the frontals and cov-
ered with skin. In others (Cavicornia) the horn cores fuse secondarily with




FIG. 665. Stomach of sheep. (After Cams and Otto.) a, abomasum (true stomach);
o, omasum (manyplies) ; re, reticulum (honeycomb) ; rw, rumen (paunch).

the frontals and are covered with a firm sheath of horn. Lastly, the horns
are outgrowths of the frontal bone, in which usually the outer coats are
lost and only the bone projects freely (antlers). These are shed yearly,
the new antler which takes its place being larger and consisting of a larger
number of branches or tines, thus constituting an index of age (Cervicornia).
CAMELOPARDALID^E (Devexa), giraffes, long-legged forms (two genera) from
Africa with persistent horns; teeth -$$ff, Giraffa. CERVID^E, deer, with
deciduous horns in the male. Cervus,* common deer; Alces,* moose;
Rangifer* reindeer; MOSCHID^E, horns lacking, males with enlarged upper
canines and with a musk gland (the source of the familiar perfume) on the
ventral surface; Moschus, central Asia. The TRAGULHWE, primitive Asiatic
and African forms, includes the chevrotain, Tragulus javanicus, the small-
est living ungulate. The CAVICORNIA include a large number of forms,
some of great economic importance; teeth fff. BOVID^E: Bos taurus,
domestic cattle, probably descended from three distinct stocks (B. primi-
genius, the aurochs, B. longifrons and B. frontosus); Bison,* including
B. europeus, the bison proper, and B. americanus* our * buffalo,' so near
extinction; Bubalus, the true buffalo of the Old World. OVHXE: Ovisaries,
sheep; 0. montana* big horn; Capra hircus, goat; Ovibos moschatus,*
musk ox. ANTILOPID^E: including a host of Old World forms (Antilope,
Oazella, Rupicapra tragus, the chamois, etc.) and Antilocapra americana,*



IV. VERTEBRATA: MAMMALIA, PROBOSCIDIA. 643



the prong horn, which sheds its horns, and Hoploceras montanus* the
Kocky mountain sheep.

Section III. TYLOPODA, stomach without manyplies, no frontal
horns, diffuse placenta. Camelus, the camels of the Old World; C. drome-
darius, one hump; C. bactrianus, two humps. Auchenia lama, A. alpaca
of South America.

Paleontology of the Ungulata.

Extensive paleontological material, especially from the tertiary rocks
of our western states, has cleared up many lines of ungulate descent
and has rendered it probable that the CONDYLARTHRA of the eocene,
with five-toed plantigrade feet, well-developed ulna and fibula, and an
omnivorous dentition, formed the stock from which descended the artio-
dactyles and perissodactyles, and possibly carnivores and primates as well,
the ungulate line extending through the Amblypoda. From one group of
these (the PHENACODONTID^E) the lines of rhinoceros and tapir have come,
and in an almost complete series we know the ancestry of the horse.
Hyracotherium (Eohippus) and Orohippus of the eocene had the fore feet
four-toed (fig. 666. 1) ; Pafaotherium and Mesohippus (2} of the lower





FIG. 666. Evolution of fore foot of horse. (From Wiedersheim.) 1, Orohippus
(eocene): 2, Mesohippus (lower miocene); 3, Miohippus (miocene); It, Protohippun
(upper pliocene); 5, Pliohippus (pleistocene); 0, Equus.

miocene and Miohippus of the later miocene were three-toed, while Mery-
hippus and Hipparion (Pliohippus, 4) of the pliocene were near the horse
in tooth structure. The single-toed horses appeared in the pleistocene
with Pliohippus (5) and then Equus itself (6). It is a peculiar fact that
the horse entirely died out in America, although the chief part of its his-
tory was enacted here.

The AMBLYPODA, mentioned above, were semi-plantigrade penta-
dactyle forms, appearing in the lowest eocene, and reaching, in Uinta-
therium (Dinocerus) an elephantine size. The TOXODONTIA of the
South American tertiaries combined perissodactyle, rodent, hyracoid, and
proboscidian features, while the TILLODONTIA of the eocene recall both
carnivores and rodents.

Order VI. Proboscidia.

The elephants and their allies, with their hoofs and herbivorous
dentition, are closely related to the ungulates. They are charac-
terized by their thick skin ( pachyderm '), the large, massive,
five-toed legs, and especially by the nose drawn out into a




644 CHORD ATA.

long proboscis with a finger-like process at the tip, lastly by
the dentition. Canines are entirely lacking, but the incisors of
the upper jaw have pulps and therefore continue to grow
throughout life, forming the well-known tusks. In the living
elephants there are but a single pair of tusks, but in some extinct
Mastodons there were a second smaller pair in the lower jaw, while

in Dinotherium only the lower in-
cisors were developed, these pro-
jecting downwards. The molars
(in Mastodon and Dinotherium
with normal replacement and
cusps) consist of numerous plates
of enamel and dentine united
FiG.667.-inside~71e7t lower jaw of b J cement, and undergo a lateral
Sff owenri, fuLtfon^mXr; 6 !; displacement. Of the three large
its successor. molars and premolars only one

at a time is functional (fig. 667, ./); when worn out the next one
behind (2) takes its place. Further features are a uterus bicornis,
a zonary placenta, and two pectoral mammas.

ELEPHANTINE : Elephas indicus, small ears ; E. africanus, large
ears. E. primigenius, mammoth, in the pleistocene ; specimens found
frozen in ice in Siberia have close woolly hair, in some places three feet
long. Mastodon, with tuberculate teeth, range from miocene through the
pliocene. DINOTHERIDJE, only lower incisors ; Dinotherium, Old World
miocene.

Order VII. Hyracoidea.

The single genus Hyrax, including species from western Asia
and Africa, with four-toed front feet, hind feet with three toes,
the digits with nails, the placenta zonary, and the dentition |~f ,
forms this group, no fossils being known. Hyrax syriacus is sup-
posed to be the ' coney ' of the Bible.

Order VIII. Sirenia.

This order consists of a few aquatic mammals which are whale-
like in form, with the fore limbs fin-like, the hind legs lacking, and