페이지 이미지

having a partial investment of enamel, and with certain peculiarities of cranial structure: the name Toxodontia is proposed for this order, all the representatives of which are extinct1.

A second remarkable order, most of the members of which have also passed away, is characterized by two incisors in the form of long tusks; in one genus (Dinotherium) projecting from the under jaw, in another genus (Elephas) from the upper jaw, and in some of the species of a third genus (Mastodon) from both jaws. There are no canines: the molars are few, large and transversely ridged; the ridges sometimes few and mammillate, often numerous and with every intermediate gradation. The nose is prolonged into a cylindrical trunk, flexible in all directions, highly sensitive, and terminated by a prehensile appendage like a finger: from this peculiar organ is derived the name Pkoboscidia given to the order. The feet are pentadactyle, but the toes are indicated only by divisions of the hoof; the placenta is annular; the mammae are pectoral.

Elephants are dependent chiefly upon trees for food. One species now finds the conditions of its existence in the rich forests of tropical Asia; a second species in those of tropical Africa. Why, we may ask, should not a third be living at the expense of the still more luxuriant vegetation watered by the Oronoko, the Essequibo, the Amazon, and the La Plata, in tropical America? Geology tells us that at least two kinds of Elephant {Mastodon Andium and Mast. Humboldtii) formerly did derive their subsistence, along with the great Megatherioid beasts, from that abundant source: two other kinds of Elephant {Mastodon ohioticus and Elephas texianus) existed in the warm and temperate latitudes of North America. Twice as many species of Mastodon and Elephant, distinct from all the others, roamed in pliocene times in the same latitudes of Europe. At a later or pleistocene period, a huge elephant, clothed with wool and hair, obtained its food from hardy trees, such as now grow in the 65th degree of north latitude; and 1 Philosophical Transactions, 1853, p. 291.

abundant remains of this Elephas primigenius (as it has been prematurely called, since it was the last of our British elephants) have been found in temperate and high northern latitudes in Europe, Asia and America. This, like other Arctic animals, was peculiar in its family for its range in longitude. The Musk Buffalo was its contemporary in England and Europe, and still lingers in the northernmost parts of America.

I have received evidences of Elephantine species from China and Australia, proving the proboscidian pachyderms to have once been the most cosmopolitan of hoofed herbivorous quadrupeds.

Both the proboscidian and toxodontal orders of Ungulata may be called aberrant: the dentition of the latter, and several particulars of the organization of the Elephant, indicate an affinity to the Rodentia; the cranium of the Toxodon, like that of the Dinothere, resembles that of the Sirenia in its remarkable modifications.

The typical Ungulate quadrupeds are divided, according to the odd or even number of the toes, into Pebtssodactyla and Aetiodactyla 1: the single hoof of the horse, the triple hoof of the tapir, exemplify the first: the double hoof of the camel, the quadruple hoof of the hippopotamus, exemplify the second. In the perissodactyle or odd-toed Ungvlata, the dorsolumbar vertebrae differ in number in different species, but are never fewer than twenty-two; the femur has a third trochanter, and the medullary artery does not penetrate the fore part of its shaft. The fore part of the astragalus is divided into two very unequal facets. The os magnum and the digitus medius which it supports are large, in some disproportionately so, and the digit is symmetrical: the same applies to the ectocuneiform and the digit which it supports in the hind foot. If the species be horned, as the Rhinoceros, the horn is single; or, if there be two, they are placed on the median line of the head, one behind the other, each being thus an odd horn.

1 From TepiiraoSdKTvXot, qui digitos habet imparea numero; and dprios, par, SaKTvXos, digitus.—Quarterly Journal of the Geological Society, No. 14, May, 1848.

There is a well-developed post-tympanic process which is separated by the true mastoid from the paroccipital in the Horse, but unites with the lower part of the paroccipital in the Tapir, and seems to take the place of the mastoid in the Rhinoceros and Hyrax. The hinder half, or a larger proportion, of the palatines enters into the formation of the posterior nares, the oblique aperture of which commences in advance either of the last molar, or, as in most, of the penultimate one. The pterygoid process has a broad and thick base and is perforated lengthwise by the ectocarotid. The crown of from one to three of the hinder premolars is as complete as those of the molars: that of the last lower milk-molar is commonly bilobed. To these osteological and dental characters may be added some important modifications of internal structure, as, e. g., the simple form of the stomach and the capacious and sacculated caecum, which equally evince the mutual affinities of the odd-toed or perissodactyle quadrupeds with hoofs, and their claims to be regarded as a natural group of the Ungulata. Many extinct genera, e. g. Coryphodon, Pliolophus, LopModon, Tapirotherium, Palozoiherium, Anciiherium, Hipparion, Acerotherium, Elasmotherium, &c, have been discovered, which once linked together the now broken series of Perissodactyles, represented by the existing genera Rhinoceros, Hyrax, Tapirus, and Equus. The placenta is replaced by a diffused vascular villosity of the chorion in all the recent genera of this order, excepting the little Hyrax, in which there is a localised annular placenta, as in the Elephant. But the diffused placenta occurs in some genera of the next group, shewing the inapplicability of that character to exact classification.

In the even-toed or 'artiodactyle' Ungulates, the dorsolumbar vertebras are the same in number, as a general rule, in all the species, being nineteen. The recognition of this important character appears to have been impeded by the variable number of moveable ribs in different species of the Artiodactyles, the dorsal vertebrae, which those ribs characterize, being fifteen in the Hippopotamus and twelve in the Camel. And the value of this distinction has been exaggerated owing to the common conception of the ribs as special bones distinct from the vertebrae, and their non-recognition as parts of a vertebra equivalent to the neurapophyses and other autogenous elements.

The vertebral formula; of the Artiodactyle skeletons shew that the difference in the number of the so-called dorsal and lumbar vertebra? does not affect the number of the entire dorso-lumbar series: thus the Indian Wild Boar has d. 13, I. 6 = 19; the Domestic Hog and the Peccari have d. 14, I. 5 = 19; the Hippopotamus has d. 15, I. 4 = 19; the Gnu and Aurochs have d. 14, I. 5 = 19; the Ox and most of the true Ruminants have d. 13,1. 6 = 19; the aberrant Ruminants have d. 12, I. 7 = 19. The natural character and true affinities of the Artiodactyle group are further illustrated by the absence of the third trochanter in the femur, and by the place of perforation of the medullary artery at the fore and upper part of the shaft, as in the Hippopotamus, the Hog, and most of the Ruminants. The fore part of the astragalus is divided into two equal or subequal facets: the os magnum does not exceed, or is less than, the unciforme in size, in the carpus; and the ectocuneiform is less, or not larger, than the cuboid, in the tarsus. The digit answering to the third in the pentadactyle foot is unsymmetrical, and forms, with that answering to the fourth, a symmetrical pair. If the species be horned, the horns form one pair, as in most Ruminants, or two pairs, as in the four-horned Antelope and Sivathere; they are never developed singly, of symmetrical form, from the median line. The post-tympanic does not project downward distinctly from the mastoid, nor supersede it in any Artiodactyle; and the paroccipital always exceeds both those processes in length. The bony palate extends further back than in the Perissodactyles; the hinder aperture of the nasal passages is more vertical and commences posterior to the last molar tooth. The base of the pterygoid process is not perforated by the ectocarotid artery. The crowns of the premolars are smaller and less complex than those of the true molars, usually representing half of such crown. The last milk-molar is trilobed.

To these osteological and dental characters may be added some important modifications of internal structure, as, e. g., the complex form of the stomach in the Hippopotamus, Peccari, and Ruminants; the comparatively small and simple cascum and the spirally folded colon in all Artiodactyles, which equally indicate the mutual affinities of the even-toed hoofed quadrupeds, and their claims to be regarded as a natural group of the Ungulata. The placenta is diffused in the Camel-tribe and non-ruminants; is cotyledonal in the true Ruminants. Many extinct genera, e. g. Cheeropotamus, Anthracotherium, Hyopotamus, Entelodon, Dtchodon, Merycopotamus, Xiphodon, Dichobune, Anoplotherium, Microiherium, &c, have been discovered, which once linked together the now broken series of Artiodactyles, represented by the existing genera, Hippopotamus, Sus, Dicotyles, Camelus, Auchenia, Moschus, Camelopardalis, Cervus, Antilope, Ovis, and Bos.

A well-marked, and at the present day very extensive subordinate group of the Artiodactyles, is called Ruminantia, in reference to the second mastication to which the food is subject after having been swallowed; the act of rumination requiring a peculiarly complicated form of stomach. The Kuminants have the 'cloven foot,' i. e. two hoofed digits on each foot forming a symmetrical pair, as by the cleavage of a single hoof; in most species there is added a pair of small supplementary hoofed toes. The metacarpals of the two functional toes coalesce to form a single ' cannon-bone,' as do the corresponding metatarsals. The Camel-tribe have the upper incisors reduced to a single pair; in the rest of the Ruminants the upper incisors are replaced by a callous pad. The lower canines are contiguous to the six lower incisors, and, save in the Camel-tribe, are similar to them, forming part of the same terminal series of eight teeth, between which and the molar series there is a wide interval. The true molars have their grinding surface marked by two double crescents, the con

« 이전계속 »