Fig. 237.
Fig.237.—Bamboo Rat.Rhizomys badius.× ¼.
Tachyoryctesis an African genus closely allied to the last. There are three Ethiopian species. It is mainly to be distinguished by the different pattern upon the grinding surface of the molars.
Fam. 5. Geomyidae.—This family of burrowing Rodents is limited to North and Central America. The animals have cheek pouches, and small eyes and ears, in accordance with their mode of life. The claws of the fore-limbs are very strongly developed.
The genusGeomyscontains some eight species, which are Central and North American, not extending, however, far north. The incisors of the upper jaw are grooved with two grooves. There are three pairs of teats—one axillary, and the two remaining inguinal.
Thomomys, without grooves on the incisors, reaches to Canada in the north, and does not extend as far south as the last genus.
Allied to this family, and indeed united with it by Tullberg, but kept separate by Thomas, is the
Fam. 6. Heteromyidae.—The members of this family are also American, but are not confined to the northern-central regions of that continent, for the genusHeteromysextends into South America.
The genusDipodomys, with twelve species, is of a Jerboa-like form, as the following measurements of an example ofD. merriamiwill show. The length of the head and body was 85 mm.; of the tail 127 mm.; the hind-foot is 32 mm. It has but four toes. The hind-limb is longer than the front-limbs.
InPerodipusthe same form is exhibited. There are, however, five toes, and the sole of the foot is hairy. The axis vertebra and the two following vertebrae are fused together.
Perognathusis a third genus. It has the same general slender form, but the tail is not so long, being but little longer than the body. The hind-limbs, too, are shorter. The teats of this and ofPerodipusare as inGeomys. The two remaining genera of the family areHeteromysandMicrodipodops.
Fig. 238.
Fig.238.—Jerboa.Dipus hirtipes.× ⅓. Eastern Europe.
Fam. 7. Dipodidae.—This family consists of small, plain-living, and leaping or arboreal creatures, commonly known as Jerboas. The main anatomical characters of the family are the following:—There is a large infra-orbital foramen. The molars are always reduced, the premolar being either absent in the lower jaw alone or in both jaws. This family presents an obvious likeness toDipodomys(hence the name of the latter) and to some other members of the American family HeteromyidaeThere is even the same ankylosis of the neck vertebrae. We find, moreover, the same association of long-legged and shorter-legged forms that characterises the Heteromyidae.
Fig. 239.
Fig.239.—Bones of right pes of Jerboa,Dipus aegyptius. × ¾.a, Astragalus;c, calcaneum;c2, middle cuneiform;c3, outer cuneiform;cb, cuboid;n, navicular; I-IV, first to fourth toes. (From Flower'sOsteology.)
The typical genusDipusis a smallish quadruped with long naked ears and a long tail. The ten species are all Palaearctic in range. The fore-limbs are short and five fingered, and the short pollex has no claw; the hind-limbs are excessively long and only three-toed. The bony structure of these limbs is remarkable. The three metatarsals are elongated almost like those of a bird, and are ankylosed together. The digits have long phalanges which alone reach the ground as the animal hops. It is a curious fact, and one not so easily identifiable with the way of life, that the neck vertebrae of this genus are ankylosed together with the exception of the atlas, which is free; the arrangement is precisely like that of the Sperm Whale. The last vertebra is, however, sometimes free. The Jerboas not only leap but they burrow, and their strong incisors are said to be used in burrowing through stony ground. They are eaten by the Arabs, and are, or have been, called Daman Israel,i.e.Lamb of Israel. InD. hirtipesthe body and tail measure respectively 4½ and 7 inches. The hind-feet have a tuft of long hairs below. Mr. W. L. Sclater's newly-founded genusEuchoreutes[339]is somewhat more primitive in its characters than isDipus. The general form is the same, with long ears and a long tail. But there are five toes to the hind-limb, the two lateral ones though nailed being much shorter than the middle three. It has a "long pig-like snout," and the tail is cylindrical as in most other Jerboas, with a tuft of longer hairs at the end. The incisor teeth, grooved inDipus, are here smooth, as inAlactaga. The species was probably obtained "in the sandy plains round the city of Yarkand."
Alactagais much likeEuchoreutes; it has five toes, a cylindrical tufted tail, the hairs at the end distichous, smooth incisors, and a premolar present in the upper jaw. It also differs fromEuchoreutesby the much smaller auditory bulla as well as in the fact that the infra-orbital foramen has no separate passage for the nerve, which passage is to be distinguished in bothDipusandEuchoreutes. The best-known species is the Siberian Jumping Rabbit,A. jaculus. Beneath the ends of the three main toes of the feet are remarkable fan-shaped pads. InA. decumanathe body and tail measure 7 and 10 inches respectively, the ears 2 inches.Platycercomys, a fourth genus of the family, is much less known and is to be differentiated from the last three genera by the fact that it has no premolars at all, the grinding tooth formula being thus 3/3. The tail too is flattened and "lancet shaped." It extends from Siberia to Nubia, and thus just enters the Ethiopian region.
The above are the more typical Jerboas. There remain several forms which are not at all Jerboa-like in their way of life, but are nevertheless, on anatomical grounds, placed with them.Zapus, an American genus, with the exception of one Palaearctic species, is transitional in that its hind-legs are rather long, but there is not so much difference between them as in the typical Dipodidae.Sminthusis at the opposite extreme toDipus. Its feet are short and of equal length; it climbs in trees, and may perhaps be looked upon as nearest of all Dipodidae to the ancestral form of the group.
Fam. 8. Pedetidae.—The genusPedetescontains but one species,P. caffer, the Cape Jumping Hare. The animal suggests a large Jerboa in appearance on account of its jumping habits, the long hind-limbs, and the long tail. The length of a fair-sized example is some 17 inches, with a tail of the same length. The eyes and ears are large. The hands are five-fingered and the feet only four-toed, the hallux being of course the absent digit. In the skeleton it is interesting to note that the second and third cervical vertebrae are so close together that there can be no free movement; interesting because inDipusthe cervicals are actually ankylosed. The dorsal vertebrae are twelve. The small intestine is long, measuring 7 feet 4 inches, while the caecum is short, being only 8 inches long. The large intestine is 3 feet 10 inches long. The gall-bladder appears to beabsent,[340]an exceptional state of affairs in Rodents. A singular fact in the anatomy of this animal is the existence of a septum dividing the lower part of the trachea. This is sometimes met with in birds. As might be supposed from its large eyes, the Spring Haas, as the animal is sometimes called, is nocturnal. Its long hind-limbs permit it to leap enormous distances. It is a burrowing Rodent.
Fam. 1. Octodontidae.—The Rodents of this family are of small to moderate size, the only, relatively speaking, giant in the family being the "Water-Rat,"Myocastor. The toes are with but one exception not reduced; the tail is long in the majority of the genera. The teats are placed high up on the sides of the body. The clavicle is fully ossified. All the genera are South or Central American in range with the exception ofPetromys.[341]
Sub-Fam. 1. Octodontinae.—Octodonhas four species, which are all Chilian, Peruvian, and Bolivian in distribution. The Degu,O. degus, has a length of 160 mm., with a tail 105 mm. long. The ears are 18 mm. long. At the roots of the claws are longish and stiff hairs which appear to serve as "combs." The tail has long but sparsely scattered hairs. There are twelve pairs of ribs. The lengths of the various sections of the intestine are as follows: small intestine, 680 mm.; caecum, 90 mm.; large intestine, 390 mm. These animals live in large companies. Closely allied is the genusHabrocoma(more correctly, as it appears, to be writtenAbrocoma), with two species.H. bennettiis 204 mm. long, with a tail of 103 mm. The ears are long, 22 mm. The fore-feet have no outward trace of the thumb. Stiff hairs like those that characteriseOctodonare found also in this genus. The fur is very soft. The furring of the tail is much thicker than inOctodon.
Spalacopuswith but a single species,S. poeppigi, is a burrowing animal, from which indeed, and on account of its resemblance toSpalax, it has received its name. The ears in accordance with the underground life are short, only 5 mm. in length in anexample of 120 mm. The tail too is reduced, being in the same example only 42 mm. in length. As in the last two genera the large intestine is about one half of the length of the small intestine.
The "Tuco-tuco," genusCtenomys, has also short ears and tail. The claws of the fore-feet are longer than those of the hind-feet.
A related form isAconaemys(better known asSchizodon), with similar external characters; it inhabits high localities on the Andes.
Petromysis the only genus of the sub-family which is not American in habitat. It is an African form and there is but one species. Its anatomy conforms to that of the genera already considered. The main difference in structure is shown by the teeth. Their surface is uneven, and differs from that of other Hystricomorphs "in that the enamel to the inside of each upper jaw-tooth and outside on each lower jaw-tooth forms two tubercles, to which correspond grooves in the reverse position of the applied teeth."
Sub-Fam. 2. Loncherinae.—The genusEchinomyswith thirteen species belongs to the Neotropical region. The members of the genus are entitled "Spiny Rats" since they have spines mixed with the fur. The tail is long and the ears are very well developed. Both feet are five-toed. The tail is scaly as well as haired.Trichomys(also calledNelomys) is very close to the above, and is also from the same part of the world.
The genusCannabateomyscontains but one species,C. amblyonyx, which was formerly included in the genusDactylomys, but has lately been separated by Dr. Jentink.[342]The animal is Brazilian and has a total length of 520 mm., of which 320 mm. belong to the tail. It is a climbing rat, and in accordance with that way of life has undergone some modifications. The fore-feet are four-toed, the two middle toes being markedly longer than the outer ones. The hind-feet are five-toed with the same greater development of the two middle toes. The claws are small and somewhat nail-like.
Dactylomys, also Brazilian, and with but one species,D. dactylinus, differs from the last in the fact that the molars are simpler in form; they are divided into two lobes, each of whichhas but a single enamel fold, whereas inCannabateomysthese teeth have several enamel folds. The tail, moreover, is but slightly hairy.
Lonchereswith eighteen species is another Neotropical genus allied to the foregoing. Small spines are, as in many of these genera, intermingled with the fur. This genus has as many as seventeen dorsal vertebrae, which is an unusually large number.L. guianaeis known as the "Porcupine Rat." Allied genera, also South American, and without spines in their fur, areMesomys,Cercomys, andCarterodon.
The South AmericanThrinacodusis also known by one species,[343]T. albicauda, which has rather more than the distal half of the long tail of a white colour. The fore-feet have four toes. The ears are broad and short.
Sub-Fam. 3. Capromyinae.—A third sub-family of the Octodontidae is formed by the generaMyocastor,Capromys,Plagiodontia, andThrynomys, which are all Neotropical forms with the exception of the last, which is African.
Thrynomys(better known perhaps asAulacodus) is a genus of African Rodent, containing some four species. The best-known of these isT. swindernianus, the Ground-Rat of West and South Africa. Its structure has been investigated by Garrod,[344]by Tullberg,[345]and by myself.[346]The fur is mingled with flattish bristles; the tail is moderately long, about half as long as the body. The fore-feet are five-toed, but the two toes at each end of the series are quite small. The hind-feet are only four-toed, the hallux being absent. The claws of the hind-feet are stronger than those of the fore-feet. The ears are not long. The limbs are decidedly short, hence the name of "Ground-Pig" sometimes applied to this animal. The molars are four in number in both jaws. The incisors of the upper jaw are twice grooved. There are thirteen dorsal vertebrae. The length of the small intestine is 60½ inches, that of the large 49; the caecum is short, being only 8 inches long. It is a remarkable fact that the acromion is joined to the rest of the spine of the scapula by a joint.
Myocastor, a name which seems to have the rights of priority over the more familiarMyopotamus, applies to a large South American aquatic Rodent. The general aspect of the animalsuggests a Water-Rat of large size (it has been exhibited in shows as a phenomenal product of London sewers!); the tail is nearly as long as the body. The ears are small. The limbs are short. The tail is naked. The hind-feet are webbed, but not so much so as inHydromys. A small thumb is present. The animal has thirteen pairs of ribs; the molars are four in each jaw. The large intestine is more than three times the length of the small, and the caecum is, as in the last genus, relatively short.
Capromysis a genus[347]which is remarkable on account of its restricted distribution. It is found only in the islands of Cuba and Jamaica. There are four species, of whichC. melanurusis a dark brown-coloured animal with a blacker tail, nearly as large as a Rabbit. The native name of this Rodent is "hutia." It is also remarkable for having a stomach more complicated than is the rule among the mammals of this group. The organ is divided by two constrictions into three compartments. InC. piloridesthe liver is occasionally divided up in an extraordinary fashion into small lobules.Capromyshas the large number of sixteen dorsal vertebrae.
Fam. 2. Ctenodactylidae.—For these African genera it seems admissible to form a distinct family, though Thomas, and Flower and Lydekker, only allow to the generaCtenodactylus,Pectinator, andMassoutierasub-family rank. On the other hand, Tullberg removed these genera entirely from the Hystricomorph section and placed them as a section of the sub-tribe Myomorphi of the tribe Sciurognathi. It was chiefly the form of the mandible which led to this placing, for in these Rodents, as in all Squirrel- and Rat-like Rodents, and unlike what is found in the Hystriciform genera, the angular process of the mandible is not bent sideways.
The genusCtenodactylusderives its name from the peculiar strong bristles which form a comb-like structure upon the hind-feet and hide the claws; these are stated to be for the purpose of dressing the fur. The Gundi of North Africa,C. gundi, has a length of 190 mm., with a short tail of 17 mm. The ears are only moderate in size. The dental formula of the molars is 4/3. The incisors are white. The feet have four digits, and the hind-limbs are the longer. The large intestine is distinctly longer than the small intestine.
Pectinator spekiiis the only representative of a genus not far removed fromCtenodactylus; it is a smallish Rodent, 6 inches in length, exclusive of a rather bushy tail nearly 3 inches long. It comes from Abyssinia. It has somewhat the appearance of a Squirrel, which is heightened by the fact that when sitting the tail is arched over the back; when running the tail is carried out straight. There are only four toes visible externally on both fore- and hind-limbs, but pollex and hallux exist in the skeleton, with a single phalanx each. There is only a single pair of mammae, and in correspondence with this but two or three young are produced at a time. The hind-feet have bristles very much like those ofCtenodactylus. The molars, however, are 4/4. There are twelve ribs, of which six reach the sternum. The latter is made up of six pieces, and the manubrium in its breadth anteriorly suggests that of the Vizcachas. The clavicles are present.[348]
Fig. 240.
Fig.240.—Carpincho.Hydrochoerus capybara.×1⁄12.
Fam. 3. Caviidae.—This family, which includes the Cavies and the Capybara, is entirely South American and West Indian in distribution. It embraces animals of fair to large size, the Capybara(or Carpincho) being the greatest of existing Rodents. The ears are well developed. The toes are commonly reduced, and the members of this family possess only a rudimentary tail. The hair though rough is not spiny. Other characters had best be deferred until the several genera are treated of. We shall begin with the giant of the family, the genusHydrochoerus. This genus contains but a single species,H. capybaraof South America. It reaches a length of some 4 or 5 feet. The ears are not large; the tail is completely absent. The fore-feet are four-toed, the hind-feet three-toed; the digits are webbed, though not to a very great degree, and the nails have the appearance of hoofs. There are fourteen dorsal vertebrae; the clavicle is absent. In the skull the paroccipital processes are of great length. The infra-orbital foramen is large. The most remarkable fact about the teeth is the great size of the posterior molar of the upper jaw; it has fourteen folds of enamel, more than all the anterior teeth possess collectively. The incisors are white and grooved in front. The measurements of the alimentary tract as given by Tullberg are: small intestine, 4350 mm.; caecum, 450 mm.; large intestine, 1500 mm.
Fig. 241.
Fig.241.—Patagonian Cavy.Dolichotis patachonica.×1⁄10.
The Capybara or Carpincho is largely aquatic in its habits. Their "favourite locality," writes Mr. Aplin,[349]"is a broad lagunain the river, furnished with open water, and also beds of 'camelotes,'—a sloping open grassy bank on one side, where the Carpinchos can lie in the daytime in the cooler weather, sleeping and basking in the sunshine; on the other a low shelving bank, clothed with 'Sarandi' scrub growing out into the black reeking mud and shallow water beyond." They always take to the water when alarmed, at a rate and with a gait which reminded Mr. Aplin of a Pig. When in the water they swim slowly with the upper part of the head, including nose, eyes, and ears, above the surface. But they can dive for a considerable time and distance, and baffle their enemies by seeking the shelter of a mass of water-plants, and lying there with their noses only just above the surface.
The genusDolichotis[350]has long ears, and generally resembles a rather long-legged Hare in appearance. The front-feet are four-toed, the hind three-toed. The Patagonian Cavy, as this animal is called, has twelve dorsal vertebrae, and rudimentary clavicles.[351]The paroccipital processes are long; the incisors are white, and are not grooved in front. The sternum has six pieces, and seven ribs reach it.
Cavia, including the speciesC. porcellus, the Guinea-pig (which name is a corruption apparently of Guiana pig), has the same number of toes on its hind- and fore-feet as has the Capybara. The name applied to the wild stock whence our Guinea-pig is derived is the Restless Cavy. The fur is greyish; of the domestic animals the colour is too well known to need description.
Fam. 4. Dasyproctidae.—The genusCoelogenysincludes but two species.C. paca, known as the "Spotted Cavy" or "Paca," has a brown body, with white spots like those of a Dasyure; it is one of the largest of Rodents, and has a quite short tail. The hand and foot are both provided with five digits; but the thumb is small, and in the foot the three middle toes considerably exceed the others in length. The hind-foot is practically three-toed. The fibula is not nearly so reduced as inDolichotis. The skull of the animal is remarkable for the extraordinary development in breadth of the jugal arch, which is sculptured externally. There is a large cavity formed below, at the maxillary end of this hugearch, by the curving inwards of the bone, which lodges a cavity continuous with the mouth. The palate has anteriorly a ridge on either side, and is thus divided from the sides of the face in a way which is not found[352]in the allies ofCoelogenys. Clavicles are present. There are thirteen dorsal vertebrae. The incisors are coloured red in front. The animal is South American, and in that continent is limited to the Brazilian sub-region. This, the best-known species of Paca, is called the Gualilla by the natives of Ecuador; in the same district another form is met with which the natives term Sachacui (signifying Forest Cavy). It is very often the case that a different native name expresses a real specific difference; and to the latter form M. T. Stolzmann has given the name ofC. taczanowskii.[353]This form, unlike the common Paca, which is fond of forests and low-lying ground in the neighbourhood of water, is alpine in habitat, living upon mountains of 6000 to 10,000 feet. It burrows in much the same way as its congener, and is greatly sought after as food, its meat possessing an "exquisite taste." It is pursued by dogs, by whose aid one of the two entrances to the burrow is guarded, and the creature is smoked out and killed with a stick.
The genusDasyprocta, containing those Rodents known as Agoutis, is divisible into several species, apparently about twelve, all of which are, like the Pacas, confined to the Neotropical region. They have, however, a much wider range within that region, and occur as far north as in Central America and in some of the West Indian Islands. They are of rather smaller size than the Paca, and are without spots. The colour is of a golden brown in some forms, but usually has a freckled, grizzled, greenish kind of appearance. The tail is stumpy, the hind-limbs are distinctly longer than those of the Paca, and the two lateral toes have disappeared from the feet—a concomitant as it seems of the Agouti's greater powers of running. The three metatarsals are closely pressed together, and the foot is as it were on the way towards the highly-modified foot of the Jerboa. The fore-feet are, however, five-toed. The clavicle is rudimentary,[354]whereas it is well developed in the Paca. The skull has not the peculiar modifications of that of the last-mentioned type. The sternum has sevenpieces, and eight ribs reach it. A curious difference between this genus and the last is in the relative proportions of the regions of the intestine. The figures given by Tullberg for the two animals are—forCoelogenys, small intestine, 4800 mm.; caecum, 230 mm.; large intestine, 21,000 mm.;—forDasyprocta agutithe same author gives: small intestine, 4200 mm.; caecum, 200 mm.; large intestine, 1000 mm. The Agouti, says Mr. Rodway,[355]is as wily as the Fox. "If chased he will run along the shallows of a creek to hide his scent from the dogs, or swim over and back again several times for the same purpose. He never runs straight when pursued, but doubles, often hiding until a dog has passed, and then making off in a different direction. Like the fox he has been hunted for a very long period, and, like Reynard, has grown wiser with every generation."
Fig. 242.
Fig.242.—Agouti.Dasyprocta aguti.×1⁄10.
Fam. 5. Dinomyidae.—The genusDinomysof Dr. Peters[356]is a very little known and remarkable form from South America allied to the Capybara, the Chinchilla, and other South American Rodents. It is only known by a single example found wandering about a courtyard in a town of Peru. It is externally like, and of about the same size as the Paca, but has a hairy tail. The animal is four-toed and plantigrade; the ears are short, and the nostrils areS-shaped. It is usually regarded as belongingto a separate family which will include but the one species,D. branickii.
Fam. 6. Chinchillidae.—This family, likewise South American, contains three genera,[357]all of which agree in having long limbs, especially the hind-limbs, and a bushy and well-developed tail. The hair is exceedingly soft, hence the commercial value of "chinchilla."
The genusChinchilla, containing but a single species,C. laniger, is a small and squirrel-like creature, living at considerable heights in the Andes. The eyes, as it is a nocturnal creature, are naturally large; and so also are the ears. The fore-feet have five toes, the hind-feet only four; they are furnished with feeble nails. The innermost toe of the hind-foot has a flat and nail-like claw. There are thirteen dorsal vertebrae, and the long tail has more than twenty. The clavicle is well developed, as in the other genera of this family. The large intestine of this animal is extraordinarily long; the proportions of the different regions of the gut are shown by the following measurements: small intestine, 820 mm.; caecum, 125 mm.; large intestine, 1340 mm. Such a disproportion between the large intestine and the small, to the advantage of the former, is a very strange fact in the anatomy of this Rodent.
The genusLagidium(also calledLagotis), which includes "Cuvier's Chinchilla," is also a mountain dweller. There are several species of this genus, which differs fromChinchillaby the complete abortion of the thumb and of the great toe. The intestinal proportions are those ofChinchilla. The ears and tail are long.L. cuvierimeasures 1½ feet in length.
Lagostomus, again, has but one species,L. trichodactylus. The animal has a tail about half the length of the body. The digits are reduced as compared withChinchilla, there being but four on the fore- and three on the hind-feet. There are only twelve dorsal vertebrae, and seven ribs reach the sternum. In the skull a distinguishing mark from the last two genera is the separation of the infra-orbital foramen into two by a thin lamella of bone. The large intestine is between one-half and one-third the length of the small intestine, and thus differs much from that ofChinchilla.
Fig. 243.
Fig.243.—Vizcacha.Lagostomus trichodactylus.×1⁄10.
The Vizcacha lives in societies of twenty to thirty members,[358]in a "village" ("Vizcachera"), a dozen or so of burrows, which intercommunicate. They lie at home during the day and come out in the evening. Their burrows, like those of the Prairie Marmot, harbour other creatures, which apparently live on amicable terms with the Vizcachas; such are the burrowing owl, a small swallow, and aGeositta. The Fox also affects these burrows, but then he ejects the rightful owner of the particular burrow which he selects. When the young Foxes are born the vixen hunts the Vizcachas for food. The Vizcacha has a most varied voice, producing "guttural, sighing, shrill, and deep tones," and Mr. Hudson doubts if there is "any other four-footed beast so loquacious or with a dialect so extensive." These animals are very friendly, and pay visits from village to village; they will attempt to rescue their friends if attacked by a Weasel or a Peccary, and to disinter those covered up in their burrows by man.
Fam. 7. Cercolabidae.—A number of the characters which differentiate this family from the Hystricidae or Ground Porcupines of the Old World are given under the description of the latter. The principal external characters are the prehensile tail, the admixture of spines with hairs, and the nature of the sole of the foot. In these points the New-World Cercolabidae differ from the Old-World Hystricidae. It is interesting to notice thatin both families we have long-tailed and short-tailed forms.Cercolabescorresponds toAtheruraorTrichys, andErethizontoHystrix.
The genusErethizon, the "Urson" of Canada, has a short, stumpy tail. Its spines are almost hidden by enveloping hair. The fore-feet have four, the hind-feet five toes. The short tail of this creature is remarkable when we reflect upon its climbing habits. It appears, however, to be a weapon with which it strikes sideways at the enemy.
Fig. 244.
Fig.244.—Brazilian Tree Porcupine.Sphingurus prehensilis.×1⁄6.
Of the Neotropical genusCercolabes(sometimes calledSphingurus,Synetheres, orCoendou) there are some eight or nine species, all found in Central and South America. The animal is arboreal, and has in correspondence with that habit a prehensile tail. The spines are not so stout as in the Ground Porcupines, and are often coloured yellowish or reddish. In correlation with its tree-frequenting habits the bones ofCercolabesshow certain differences from those of the Ground Porcupines. The scapula is broader and rounder in front than is that ofHystrix; the phalanges of the thumb (which is rudimentary) are fused together as in the CanadianErethizon; but those of the very small hallux are also fused, whereas inErethizon, as inHystrix, they are separate. In one species,C. insidiosus, Sir W. Flower states that there are as many as seventeen dorsal vertebrae and thirty-six caudals. The tail is thus very long. InC. villosusthere are fifteen dorsals and twenty-seven caudals; eight ribs reach the sternum, which is composed of seven pieces, thesixth being very small. The clavicles are well developed. A curious fact aboutC. villosusis that the acetabular cavity is perforate (on both sides), or at least only closed by membrane. In many forms of Rodents the bone is very thin in this region. This fact perhaps lessens the significance of the perforation of the acetabulum ofEchidna(see p.109).
Of the allied genusChaetomys, also Neotropical, there is but a single species, which inhabits Brazil. It has a nearly completely closed orbit, a feature which differentiates it from the last animal, and one which also shows it to be a more modified form. The spiny covering is less pronounced than in its allies.
Fam. 8. Hystricidae.—This family is characterised by the fact that all its members possess spines; but the tail, if at all long, is not prehensile, and the soles of the feet are smooth and not covered with rough tubercles, as in the Tree Porcupines of the next family, Erethizontidae. The clavicle is less developed than in the arboreal forms. In the organs of digestion there are points of a family difference between the two groups of spiny Rodents. The tongue has serrated scales arranged in transverse rows, which are directed backwards. A gall-bladder, though not always present, is sometimes found; it apparently never exists in the arboreal Porcupines and inErethizon. The lungs show a great tendency to subdivision, which appears to be especially marked in the genusAtherura. The caecum seems also to be shorter in the Ground Porcupines. InHystrix cristatathe small intestine measures 15 feet 7 inches; the caecum, 8 inches; the large intestine, 4 feet 4 inches:—inAtherura africanathe caecum measures 7½ inches; the large intestine, 1 foot 10 inches. The corresponding measurements ofSynetheres villosuswere: small intestine, 7 feet 3 inches; caecum, 1 foot 4 inches; large intestine, 2 feet 7 inches. InErethizonthe caecum is 2 feet 4 inches in length. These differences are too large and too constant in a number of presumedly allied forms to be overlooked.
Mr. Parsons has directed attention[359]also to a number of muscular differences, such indeed as might be expected to occur between animals of such different habits.
The genusHystrixembraces the better-known Porcupines. It is a genus of wide range, extending from the East Indies to Africa,and even occurring in Europe. There are several species, of which the commonHystrix cristatais the best known, and is the one which is to be found in Europe.
Fig. 245.
Fig.245.—Common Porcupine.Hystrix cristata.×1⁄10.
The spines of the common form and of the others are solid in the middle of the body, but on the tail they are expanded into hollow quills, which make much rattling. They are as a rule black and white, the middle of the spine being banded with black. A great crest of coarse long hairs on the head is responsible for the scientific name of the well-known form. Sometimes in this genus, as in the Tree Porcupines of Brazil, the spines are orange or yellow; but it is said that the colour is soon lost in this country. As a matter of fact it is the easiest thing in the world to wash out with ordinary tap-water much of the yellow colour of the spines of the South AmericanSphingurus. The same may be the case with the pigment of the Old-World Porcupines. There are fourteen to fifteen dorsal vertebrae and four or five lumbars. The tail varies in length, but is shorter than the long tail of the arboreal New-World forms. It seems impossible when mentioning the Porcupine to escape from some observations about its alleged habit of shooting its quills. For some reason or other Buffon has got the credit of inventing, or atleast promulgating, this legend, which has even grown so in the telling that the quills are said to be capable of penetrating planks of wood. What Buffon saidaproposof this matter is, "The marvellous commonly is pleasingly believed, and increases in proportion to the number of hands it passes through." It is of course the rattling of the spines and the occasional falling out of loose ones which has started the legend. They are, however, excellent weapons of offence, and the animal charges somewhat backwards to make the best use of them against the foe. The spines, however, are by no means an absolute protection, since, as Mr. Ridley informs us,[360]Tigers will kill and eat these animals just as the Thylacine is apparently indifferent to the spiny armature ofEchidna.
Of the Brush-tail Porcupine,Atherura[361]there are at any rate two species, the West AfricanA. africanaand the MalayanA. fasciculata. It is interesting that the gap in the present distribution is partially filled by the discovery of fossil teeth near Madras. The genus does not differ widely in external appearance fromHystrix; it has, however, a rather longer tail; there are fewer large spines, and there is a tuft of them at the end of the tail, whence is derived the name of the genus. The frontal bones project a little distance between the nasals, a feature which does not seem to appear in the true Porcupines. There are fourteen dorsal vertebrae and five lumbars. The twenty-four caudal vertebrae of this Porcupine shows how much longer is its tail than that ofHystrix; for in the latter twelve is about the number.
A third genus of Old-World Porcupine is the singularTrichys.[362]Of this there is but one species,T. lipura. It is a curious fact that out of three examples, all from Borneo, two were quite without a tail. But this appears to be merely a mutilation, though it is singular that the natives state it to be without a tail. One cannot help thinking of the way in which lizards sometimes shed their tails when pecked at. The tail of this genus is more than half the length of the body and head.Trichyshas sixteen dorsal and six lumbar vertebrae. There is a tuft of quills at the end of the tail, which are thin and compressed,though truncate at the free extremity and hollow; they represent in a more rudimentary way the much stronger tuft at the end of the tail of other Porcupines. It is a curious fact that this and other Porcupines possess a mechanism for warning their foes precisely comparable to that of the rattlesnake. There are sixteen dorsal vertebrae.
The chief feature of this group is the existence of two pairs of incisor teeth in the upper jaw, of which the inner are very small and lie behind the outer. In the skull the infra-orbital foramen is small; the incisive foramina are very large. The tail is short or absent.
Fam. 1. Leporidae.—This family is distinguished from the Lagomyidae by the long ears, by the tail, which is present, though short, and by the longer limbs. There are six teeth belonging to the molar series in the upper jaw, and five of the same in the lower. The clavicle is imperfect.
The longest known genus of this family,Lepus, was, until the quite recent discovery ofRomerolagus, the only genus. It is of universal range, excepting Australasia and Madagascar, and consists of about sixty species. These are the Hares and Rabbits, to the former being assigned the longer-limbed forms.
As every text-book of zoology contains a more or less elaborate account of the structure of the Common Rabbit, and as there is but little structural difference between the members of the genus, a short account of the generic peculiarities ofLepuswill suffice here. The fore-feet are five-toed, the hind-limbs four-toed. The hairy integument enters the mouth cavity, and the inside of the cheeks have a hairy covering. The soles of the feet are, moreover, hairy. The maxillary bones are curiously sculptured.
Fig. 246.
Fig.246.—Lepus cuniculus.Skull.A, Lateral view;B, ventral view.ang.pro, Angular process of mandible;as, alisphenoid (external pterygoid process);aud.me, external auditory meatus;b.oc, basioccipital;b.sph, basisphenoid;cond, condyle;cor, coronoid process;fr, frontal;int.pa, inter-parietal;ju, jugal;lcr, lachrymal;max, maxilla;nas, nasal;opt.fo, optic foramen;o.sph, orbitosphenoid;pa, parietal;pal, palatine;pal.max, palatine plate of maxilla;pal.p.max, palatine process of premaxilla;par.oc, paroccipital process;peri, periotic;p.max, premaxilla;pt, pterygoid;p.t.sq, post-tympanic process of squamosal;s.oc, supraoccipital;sq, squamosal;ty.bul, tympanic bulla;vo, vomer;zyg.max, zygomatic process of maxilla. (From Parker and Haswell'sZoology.)
The Common Rabbit,L. cuniculus, differs from the Common Hare in the comparatively shorter ears and legs. The ears have not, to so marked a degree, the black tips of those of the Hare. The animal, moreover, produces naked young, and lives in burrows of its own excavation. A difference in the structure of the caecum, which distinguishes the Rabbit from the Hare, has beenpointed out by Professor W. N. Parker.[363]These differences have led some to approve of its separation from the Hares into a genusOryctolagus. This animal is believed to be an introduced species, and to have been brought by man into these islands. Its original home is the Spanish Peninsula, the south of France, Algiers, and some of the Mediterranean islands. Mr. Lydekker thinks that the only other species ofLepuswhich can be considered to be a "Rabbit" is the AsiaticL. hispidus.
Of Hares there are two species in this country. The Common Hare,L. europaeus(the nameL. timidusseems to be really applicable to another species to be referred to presently), extends all over Europe excepting the extreme north of Russia and Scandinavia. It is not known in Ireland, and, curiously enough, attempts to acclimatise this animal in that island have failed—a state of affairs which contrasts with the fatal ease with which the Rabbit has been introduced into Australia. Ireland has, however, the Variable Hare,L. timidus(also calledL. variabilis), a species which is common in other parts of Europe, and which extends as far east as Japan. This species differs from its ally by the fact that it often turns white in winter with the exception of the black tips to the ears. In Ireland this change does not always occur; but Mr. Barrett-Hamilton has commented upon the fact that Hares of this species do change on Irish mountains. It appears that in this animal the change from the winter to the summer dress is accomplished by the actual casting off of the white hairs and their replacement by a fresh growth of "blue" hairs. A similar change occurs in the AmericanL. americanus.
Dr. Forsyth Major has noted the fact that the various species of Hares can be distinguished by the condition of the furrows upon the upper incisors. Thus two African species,L. crawshayiandL. whytei, are to be separated by the fact that in the former the incisors are quite flat, whereas inL. whyteithe groove is more prominent and there is a second shallow furrow.
The genusRomerolagus[364]is quite a recent discovery. It occurs on the slopes of Popocatepetl in Mexico; it has the general aspect of the last genus, and is spoken of as a "Rabbit." It inhabits runs in the long grass which clothes the sides of themountain. Externally it is something like the Pikas, since it has no tail visible. The ears, too, are short, and the hind-legs comparatively short. The skull is very like that of the Rabbit; but in other osteological details it is aberrant. Thus the clavicle is quite complete, and only six ribs articulate with the sternum, instead of the seven that we find in the Rabbit.
Fam. 2. Lagomyidae.—The animals of this family are smaller than the Hares and Rabbits; they have short Vole-like ears and no external tail. The limbs also appear to be shorter. As there is but a single genus, the characters of the family may be described in connexion with those of the genus, which is known asLagomys(apparently more correctlyOchotona). Of this genus there are about sixteen species, which are mainly Asiatic; one species extends its range into Eastern Europe, and three are North American.
The skull has not the supra-orbital grooves of the Rabbits, and has a well-marked backward process of the zygomatic arch. There are eighteen dorsal vertebrae. The molars and premolars are five.
The vernacular names of "Pika" and "Piping Hares" have been applied to the members of this genus, the latter on account of their peculiar call. They live among rocks in companies and they burrow. They are usually found at considerable altitudes: thusL. roylei, the "Himalayan Mouse Hare," is found at elevations as high as 16,000 feet; whileL. ladacensisgets even higher, 19,000 feet having been recorded. With the habits of a Marmot, so far as concerns living in burrows and at great altitudes, the animals of this genus, with their squat form and short ears, are not unlike those animals. In the past this genus occurred more generally over Europe. Species from Miocene beds have been met with in England, France, Germany, and Italy.
Fossil Rodents.—Quite a large number of existing genera of Rodents are known from even the earlier strata of the Tertiary period. The Squirrels (and even the genusSciurusitself) occur in the Upper Eocene. So, too, do the generaMyoxus, and (in South America)Lagostomus.Spermophilus,Acomys,Hystrix,Lagomys,Lepus,Hesperomysare known from Miocene rocks.Rhizomys,Castor,Cricetus,Mus,Microtus, and some others appear to have originated so far as we know in the Pliocene, while a still larger series of existing genera are Pleistocene. It is interestingto note that some of the extinct genera were much larger than recent forms. At present,Hydrochoerusis the biggest Rodent; but the genusMegamysfrom the Pampas formation of Argentina was "nearly as large as an ox." The wider range of genera in the past is illustrated byHystrix, which, now an Old-World form, is represented by remains in the Miocene and Pliocene of America.
It is a significant fact that of living generaSciurusis the oldest; for it has been pointed out that in a number of features the Squirrels are among the most primitive of Rodents. The zygomatic arch is slender, and has thus not acquired the specialisation that is to be found in that part of the skull in other Rodents; moreover, the "jugal bone is not supported by any process from the maxilla exactly as in the primitive Ungulata." The feet, too, are unspecialised, though that is the case with many other genera. It may also be pointed out that the teeth bear not a little likeness to those ofOrnithorhynchusin their multituberculate character.
Some few fossil forms have already been dealt with in the preceding pages.
The two generaCastoroidesandAmblyrhiza, from the Pleistocene of North America and the West Indies, are usually regarded as forming a family. The skull of the former genus indicates an animal of the size of a Bear. It is compared to that ofCastor, but it has a wide infra-orbital foramen. The teeth are four in each jaw, and are formed of three to five lamellae; the incisors of this animal are powerful but short.Amblyrhiza, on the other hand, has long incisors which are longitudinally grooved anteriorly. It has a free fibula. This latter as well as other characters have led Tullberg to remove it from association withCastoroides.
This group of Eocene mammals is to be defined by a number of characters, of which the more important are the following:—The incisors are enlarged, grow from persistent pulps, and are coated with enamel upon the outer surface only; they are those of the second pair only, the first and third having disappeared or become small. The canines are reduced in the later forms.