Section 2. Myomorpha.

This subdivision of the Rodents contains, according to Mr. Thomas's recent estimate, no less than 102 genera. It is therefore obviously impossible to do more than refer to some of the more interesting of these. This group is again divided into the following families:--

(1) Gliridae, including the Dormice.

(2) Muridae, the Rats, Mice, Gerbilles, Australian Water-rats, Hamster.

(3) Bathyergidae, Cape Mole, etc.

(4) Spalacidae, Bamboo Rats. {470}

(5) Geomyidae, Pouched Rats.

(6) Heteromyidae, Kangaroo Rats.

(7) Dipodidae, Jerboas.

(8) Pedetidae.

The Gliridae have no caecum, so usual in the Rodentia. It is true that all the genera have not been dissected, but it is known that in the true Dormice, as well as in the genus Platacanthomys, a caecum is absent.

Apart from these few exceptions the Mouse-like Rodents all possess a caecum, though it is often not very large. They are all smallish animals, and are modified to a great variety of habit and habitat. There are burrowing, swimming, and climbing forms. The group is universal in range, even including the Australian region, in which they are the only Rodents.

FAM. 1. GLIRIDAE.--This family, also called Myoxidae, includes the Dormice, and is entirely an Old-World family, absent only from the Malagasy region. Its most important differential character is the total absence of the caecum and of any sharp boundary between the small and large intestine. The molars are usually four. The eyes and ears are well developed.

The genus Muscardinus includes only the Common Dormouse, M. arellanarius. This small creature, 3 inches long with a tail of 2-1/2 inches, is, of course, a well-known inhabitant of this country. It is also found all over Europe. It is not particularly abundant in this country, and a good specimen is said to be worth half a guinea. As the specific name denotes, it lives largely on hazel nuts; but it will also suck eggs and devour insects. The animal makes a "nest" in the form of a hollow ball. Its hibernation is well known, and has also given rise to the German name ("Schlaefer") of the group. It was well known to Aristotle, who gave or adopted the name [Greek: Eleios] for the animal. Its winter sleep--suggestive of death--and its revivification in the spring gave the Bishop of Salamis, Epiphanius, an argument for the resurrection of man. The fur was reckoned in Pliny's time a remedy for paralysis and also for disease of the ears.

The genus Myoxus includes also but a single species, M. glis, the so-called "Fat Dormouse" of the Continent. It has no {471} glandular swelling at the base of the oesophagus, such as occurs in the last genus and in Graphiurus. Of Graphiurus there are thirteen species, all African in range. The genus does not differ widely from the last. There is, however, a glandular region of the oesophagus. Eliomys is the last genus of typical Dormice. It is Palaearctic in range.

Platacanthomys, of a Dormouse-like form, has like other Dormice a long tail, on which the long coarse hairs are arranged in two rows on opposite sides towards the tip; it is represented by a single species, P. lasiurus, from the Malabar coast. It is arboreal in habit. The fur is mingled with flattened spines. The molars are reduced to three on each side of each jaw. This form has been bandied about between the "Mice" and the "Dormice"; but Mr. Thomas's discovery of the absence of the caecum argues strongly in favour of its correct location among the Gliridae. Typhlomys is an allied genus, also from the Oriental region. This and the last are placed in a special sub-family of the Gliridae, Platacanthomyinae, by Mr. Thomas.

FAM. 2. MURIDAE.--This family, that of the Rats and Mice in a wide sense, is the most extensive family of Rodents. In it Mr. Thomas includes no less than seventy-six genera. The molars are generally three. The tail is fairly long, or very long, and the soles of the feet are naked.

SUB-FAM. 1. MURINAE.--The true Rats and Mice may be considered to form a sub-family, Murinae. The genus Mus, including the Rats and Mice in the limited sense of the word, contains about 130 species. They are exclusively Old World in range, being only absent from the Island of Madagascar. In the New World there are no species of the restricted genus Mus. The eyes and the ears are large; the pollex is rudimentary, and bears a nail instead of a claw. The tail is largely scaly. All the members of the genus are small animals, some quite minute. In this country there are five species of the genus, viz. the Harvest Mouse, M. minutus, which has a body only 2-1/2 inches long with an equally long tail. It is the smallest of British quadrupeds with the exception of the Lesser Shrew. The Wood Mouse, M. sylvaticus, is about twice the size; it differs also from the last species in that it {472} frequents barns, and is thus sometimes mistaken for the Common Mouse, from which, however, it is to be distinguished by its coloration and longer ears. The latter, M. musculus, is too familiar to need much description. A curious variety of it has occurred. This has a thickened and a folded skin like that of a Rhinoceros, and the hair has disappeared. The Black Rat, M. rattus, is like a large Mouse, and is smaller and blacker in colour than the "Hanoverian Rat." It is sometimes called the "Old English Rat," but seems nevertheless to be not a truly indigenous Rodent. It has been so defeated by competition with the Hanoverian Rat that it is now not a common species in this country.

The Hanoverian or Brown Rat, M. decumanus, is a larger and a browner animal than the last. It is very widely distributed through the globe, no doubt largely on account of the fact that it is readily transported by man. The same is the case with the Common Mouse, whose real origin must be a matter of doubt. The original home of the Brown Eat is thought by Dr. Blanford to be Mongolia. There is so far a justification for the name "Hanoverian Rat" that the animal seems to have reached this country about the year 1728. But there is no reason for calling it, as is sometimes done, the Norway Rat.

Some members of this genus, whose fur is interspersed with spines, or which are quite spiny, have been separated as a genus, Leggada, which, however, is not generally allowed.

Closely allied again is Chiruromys, which has a strongly prehensile tail, a feature which is not common among the Myomorpha, though Dendromys, a tree-frequenting form, and Mus minutus, already spoken of, show the same character. Many Mice seem to have prehensile tails, which they can curl round branches; but it is not so fully developed as in the species just named.

A number of other genera are referable to the true Mice, the sub-family Murinae of Thomas's classification. The Syrian and African Acomys has very spiny fur, so much so that "when it has its spines erected it is almost indistinguishable at the first glance from a diminutive hedgehog." The genera Cricetomys, Malacomys, Lophuromys, Saccostomus, Dasymys are restricted to the Ethiopian region. Nesokia is Oriental, reaching {473} also the Palaearctic region. Vandeleuria, Chiropodomys, Batomys, Carpomys are Oriental, the last two being confined to the Philippines.

Another peculiar Philippine genus is Phlaeomys, of large size, and allied to it is Crateromys, originally confounded with it. Batomys granti is also confined to Luzon. Its molars are three, like those of the also restricted and Philippine Carpomys melanurus, which is an arboreal form. There is a second species, C. phaeurus.

Phlaeomys is placed, however, by Mr. Thomas in a distinct sub-family of its own, PHLAEOMYINAE, and is removed from the Murinae.

Hapalomys, with but one species, is Burmese. Pithecochirus is Javanese and Sumatran. Conilurus (also known as Hapalotis) is a genus containing species which are termed Jerboa Rats, on account of their mode of progression. They are desert and Australian forms. There are sixteen species.

FIG. 235.--Spiny Mouse. Acomys cahirinus. x 1/2.

Mastacomys, with one species, is limited to Tasmania. Uromys, with some eight species, is from Queensland, and inhabits also the Aru Islands and the Solomon Islands. The Celebesian Echiothrix, or Craurothrix as it should apparently properly be called, is another genus containing but a single species. Golunda is both Oriental and Ethiopian, one species occurring in each region. The beautiful little striped Barbary Mice, Arviacanthis (or Isomys), are African, north as well as tropical.

The genus Saccostomus resembles the Hamsters in the presence of cheek pouches. Its teeth, however, are Murine. It agrees with Steatomys in the comparatively short tail. The caecum is rather long. {474}

SUB-FAM. 2. HYDROMYINAE.--The genus Hydromys, of which there are several species, the best known being H. chrysogaster, is an exclusively Australian form, and is aquatic in habit. It is a foot or so in length, and has a fairly long tail. The fore- and hind-limbs are webbed, in correspondence with its habits. The Australian Water-Rat is black, with an admixture of golden-coloured hairs dorsally and golden colour below, with a lighter median stripe. The thumb is small, and the webbing of the hands is not so marked as is that of the feet. The molars are only two in each half of each jaw. The caecum is rather small, the measurements of the alimentary canal being: small intestine, 895 mm.; large intestine, 278 mm.; caecum, 70 mm. Allied to the last is Xeromys, a genus which is also Australian, but limited to Queensland. It has been established by Mr. Thomas, who discovered that it has the same reduced formula as Hydromys. Xeromys, however, is not an aquatic animal, and has unwebbed feet.

In the Luzon highlands Mr. Whitehead has discovered, and Mr. Thomas quite recently described, a number of peculiar Rodents. Of these the genera Chrotomys, Celaenomys, and Crunomys are allied to the Australian and New Guinea Hydromys.

Chrotomys whiteheadi is unusual among Muridae, in its coloration being marked by a pale stripe down the back. The creature is the size of the Black Rat (Mus rattus). It is terrestrial not aquatic in habit, in spite of its likeness to Hydromys. The molars, however, are 3/3.

Crunomys fallax is more like Hydromys. It has, however, three molars, as in the last genus. But the skull has the flattened form characteristic of Hydromys as opposed to Mus.

Like Batomys, Celaenomys silaceus is also somewhat intermediate between Hydromys and Mus. It is described as very Shrew-like in appearance, and has a very pointed muzzle. Its habits Mr. Whitehead is "quite unable even to guess at." Like Hydromys and Xeromys this Rodent has but two molars.

SUB-FAM. 3. RHYNCHOMYINAE.--The genus Rhynchomys, containing but one species, Rh. soricioides (of Thomas), is also, as both its generic and specific names imply, a somewhat Shrew-like form in external aspect. The skull, too, is Insectivore-like in its {475} elongation, and the lower incisors are worn to needle-like points. The two molars are excessively minute, and thus the always large gap in the jaws is greatly exaggerated. It is suggested that this Rat is an insect-eater, but nothing positive is known.

SUB-FAM. 4. GERBILLINAE.--The Gerbilles form another sub-family, Gerbillinae, of the Muridae, or a family, according to some. The best-known genus is Gerbillus, including the Gerbilles proper. These animals are Old World in range, belonging to the three regions of that part of the world. There are a large number of species in the genus, over thirty. They have a Jerboa-like form, with rather long hind-limbs and a long and hairy tail. But the hind- as well as the fore-feet are five-toed. The molar teeth have no trace of tubercles, but only transverse lamellae of enamel. The incisors are orange; they are white in Dipus. Gerbillus pyramidum is 90 mm. long, with a tail of 125 mm. The ears are long, 13 mm. The tail has longer hairs at the tip.

FIG. 236.--Gerbille. Gerbillus aegyptius. x 1/2.

Psammomys is in some respects different. The tail is shorter than in Gerbillus; its length in an individual of 165 mm. was 130 mm. As in Gerbillus there are four pairs of teats, two pectoral and two inguinal. This genus is exclusively Palaearctic in range. Meriones has a range co-extensive with that of Gerbillus.

Pachyuromys is an Ethiopian genus with a short tail. As the generic name denotes, the tail is not only short but thick and fleshy.

SUB-FAM. 5. OTOMYINAE.--The allied genera, Otomys and Oreinomys, are Ethiopian. Otomys unisulcatus has a tail shorter than the body, the measurements of a female of this species being 137 mm. with a tail of 87 mm. The ear is long, whence the name; it measured in this specimen 20 mm. {476}

SUB-FAM. 6. DENDROMYINAE.--The genus Deomys is an African form, consisting of only one species from the Congo region. D. ferrugineus has a reddish colour as its name implies; the soles are quite naked and the tail is long and slender. It is considerably longer than the body, measuring (minus a fragment of the tip) 172 mm., while the body is 125 mm. long. The characters of the molar teeth, which are three, are intermediate in their form between those of the true Rats and those of the Hamsters.

Dendromys is also Ethiopian in range. There are several species. D. mesomelas is a smallish creature, 60 mm. long, with a tail of 90 mm.

Steatomys is another African genus, allied to the last. Its tail, however, is only half the length of the body. The two remaining genera are Malacothrix and Limacomys. Their range is African.

SUB-FAM. 7. LOPHIOMYINAE.--Allied to the Hamsters is the singular East African genus Lophiomys, with only one species, L. imhausi, of Milne-Edwards. The size is between that of a Rabbit and of a Guinea-pig. The stomach is curved and somewhat intestiniform. It has been termed the Crested Rat on account of the "prominent crest of stiff hair running down the back." The fingers and toes are five, and the very long tail is clad with hair longer than that upon the body generally. The pollex is rudimentary, and the hallux is opposable.

The most remarkable structural feature in this genus concerns the skull, and on account of this it has been regarded as the type of a separate family. The temporal fossa behind the eye is covered over by a complete bony plate, formed by a downgrowth of the parietal, meeting an upgrowth from the malar; this singular arrangement of the bones recalls the conditions which obtain in turtles. The whole skull, moreover, is covered with symmetrically disposed granulations, such as are found in no other mammal; it suggests rather the skull of certain fish. It is believed that the bony plate already referred to is not really a portion of the bones of which it appears to be a prolongation, but merely an ossification of fasciae in this region. The atlas is granulated like the skull; there are sixteen pairs of ribs and a feeble clavicle. The molars are three, and of a peculiar form. {477} They have, in the case of the first three, transverse ridges, from which stand up two sharp and long tubercles. The other teeth have two ridges. The incisors are pale yellow. The shape of the teeth and the smallness of the caecum suggest that this Rodent is not so purely a vegetarian as others, and that it nourishes itself largely upon insects.

SUB-FAM. 8. MICROTINAE.--The Voles or Water-Rats form a distinct group of Murine animals, to which the sub-family name of Microtinae has been applied from the genus Microtus (more generally known as Arvicola), a genus which includes the Water-Rat and Field-Voles of this country. This genus has short ears, and a short and hairy tail. Its build is stouter and clumsier than that of the Rats. The genus is confined to the Palaearctic and the Nearctic regions. In this country there are three species. The best known is the Water-Vole or Water-Rat, M. amphibius, which has been seen by most people, and which frequents streams, ponds, and canals. The feet, curiously enough, are not webbed, which seems to argue the recent adoption of an aquatic life. Mr. Trevor-Battye has remarked that this animal, when swimming at leisure, uses its hind-limbs only, carrying the fore pair at the sides like a Seal. The Bank-Vole, M. glareolus, is rather a local species in this country. It is a terrestrial Vole, and burrows. The Field-Vole, M. agrestis, has become notorious on account of the "plagues," to which its immense numbers have on occasions given rise. It is the smallest species, and has a greyish-brown fur like the Water-Vole, the Bank-Vole being redder. To give an idea of the cost of the depredations of this animal, Mr. Scherren quotes a farmer who gave evidence before the Agricultural Commission to the effect that, putting the damage of one Vole at two pence, the amount of loss suffered on a farm of 6500 acres in two years would be L50,000!

The genus Fiber comes very near the last. It is a North American genus. The hind-feet are slightly webbed; the tail is a trifle shorter than the body, and is compressed and scaly, with scattered hairs. The thumb is short, but with a fully-developed claw. As in the last genus, the small and large intestines are roughly of the same length, and the caecum is about one-fourth of the length of either. It is known as the "Musquash." {478}

Of Fiber zibethicus, or rather a closely-allied form, F. osoyoosensis, from Lake Osoyoos near the Rockies, Mr. Lord writes that it constructs for itself a house of bulrushes built up from the bottom in 3 or 4 feet of water. It is dome-shaped, and rises about a foot out of the water. "If a dead or badly-wounded duck be left on the pool, it is at once seized on, towed into the house, and doomed." Thus it appears that this Rodent, like so many others, is largely carnivorous. It has also been asserted that it eats fish.

Neofiber is an allied genus, North American in range. The species, N. alleni, is compared, as regards outward form, with the Water-Vole, M. amphibius. It has, however, a shorter tail.

Another very well-known member of this sub-family is the Lemming. The name, however, applies to two quite distinct genera. The genus Cuniculus, including the Banded Lemming, C. torquatus, is an inhabitant of North America, Siberia, and Greenland. The tail is short, its length being 12 mm. as against a body length of 101 mm. The feet are furred beneath, a not unusual state of affairs in Arctic mammals. The ears are very slight. The thumb is well developed, and bears a claw.

In Myodes, on the other hand, which is not so markedly an Arctic animal, though occurring in both Palaearctic and Nearctic regions, the ears are rather bigger, though still smaller than those of Microtus. The under surfaces of the feet are similarly furred. The tail is also short. It is commonly said that the two genera are to be distinguished by the furred feet of Cuniculus, and by the absence of fur in the present genus. That, according to Tullberg, does not appear to be the case. The differences are thus so much reduced that it seems almost unnecessary to retain the two genera. The best known species of Myodes is of course the Scandinavian Lemming, M. lemmus. This animal used to occur in this country in Pleistocene times (as did also C. torquatus), and recently Dr. Gadow has found remains with skins attached in caves in Portugal. It may still survive in the mountains of the Peninsula.

The actual habitat of the Lemming in Scandinavia is the great tablelands, 3000 feet high in the centre. The migrations do not take place with regularity; even twenty years may elapse before the appearance in cultivated lands of those countless {479} hordes so familiar (as far as their description is concerned) to everybody. The Lemmings do not return from their exodus. They die from various causes, including combats with one another. Their chief foes, however, are Wolves and Gluttons, Buzzards and Ravens, Owls and Skuas, which batten on the migrant hordes. Their sudden increase in numbers recalls the similar increase at times of the Field-Vole, to which reference has already been made.

Ellobius is an Old-World genus, which leads a "Talpine" life, and has in consequence rudimentary external ears and very small eyes. The tail is short. Contrary to what might be expected from its mode of life, the claws upon the digits are not strong.

The remaining genera of Vole-like Murines are Phenacomys and Synaptomys from North America, and Siphneus from Palaearctic Asia. Evotomys is one of those genera which are common to both the Palaearctic and the Nearctic regions, but the bulk of the species are North American.

SUB-FAM. 9. SIGMODONTINAE.--This is the name given to another sub-family of Murine Rodents, a group which includes the Hamsters in the Old World as well as a large number of South American genera of Rat-like animals. Of these latter there are a very large number, the bulk of the group being American.

The Hamsters, genus Cricetus, as it is usually called, although apparently the correct name is Hamster, are Old-World forms of Pouched Rats. The Common Hamster, C. frumentarius, is about 210 mm. long, with a tail of 58 mm. It has cheek pouches. The small and the large intestines are not very unequal in length, and the caecum is fairly large, being about one-sixth to one-seventh of the length of either. It is a purely vegetable-feeding creature, and in Germany where it occurs (and from which language its vernacular name is derived), hibernates during the winter in its burrow, having previously surrounded itself with a great accumulation of food carried thither.

To North America are peculiar the genera Onychomys, Sigmodon, and Peromyscus. The genus Sigmodon, the Cotton Rats, reaches Central America, and even gets a little farther south. The other two genera, though mainly North American, also extend their range to the south. Onychomys has hairy {480} foot-pads, a state of affairs which characterises a number of these Rodents.

The genera Megalomys, Chilomys, Reithrodontomys, Eligmodontia, Nectomys, Rhipidomys, Tylomys, Holochilus, Reithrodon, Phyllotis, Scapteromys, Acodon, Oxymycterus, Ichthyomys, Blarinomys, Notiomys are South American forms. Oryzomys and Rheithrodontomys are common to both parts of the New World.

The genus Ichthyomys is remarkable on account of its un-Rodent-like habits and of certain associated structural changes. I. stolzmanni was obtained from Mount Chanchamays in Peru at an altitude of 3000 feet; it is a habitual fish-eater, and lives in streams. Another species, I. hydrobates, was formerly referred to Habrothrix. The skull shows likenesses to that of the Australian Hydromys; but the most marked characters of adaptation are those of the teeth and caecum. The cutting edges of the upper incisors form a reversed of obvious use in holding a slippery fish. The caecum is much reduced, short, and narrow. The general Otter-like shape of the creature is largely due to its flattened head, though its "size and general proportions are much as in the common Black Rat."

This sub-family contains a number of genera from Madagascar, viz. Brachytarsomys, Nesomys, Hallomys, Brachyuromys, Hypogeomys, Gymnuromys, and Eliurus.

SUB-FAM. 10. NEOTOMINAE.--The last sub-family of the Muridae is that of the Neotominae, containing the North American genera Neotoma, Xenomys, Hodomys, and Nelsonia.

FAM. 3. BATHYERGIDAE.--This family contains several genera which consist of subterranean forms. All these Rodents agree in a number of characters, of which the principal are as follows:--

The eyes are very small, and the external ears are reduced to the merest fringe of skin round the aural aperture. The legs are short, as is the tail; the hair-covering is reduced--a reduction which finds its culmination in the nearly nude Heterocephalus. Being burrowing creatures, a number of other modifications in accordance with this mode of life are to be seen in their structure. The upper incisors stand out in front of the closed lips, and prevent the entrance of earth. For the same reason {481} the nostrils are small, and the forehead but little expanded between them.

The genus Bathyergus contains but a single species, the Cape Mole-Rat, which is found in Southern Africa; it is of moderate size, not exceeding a small Rabbit in dimensions. On the fore-limbs are exceedingly long claws, of which that borne by the second finger is the longest, and the claw of the thumb the shortest. The hind-feet have by no means such long claws. The scratching and burrowing is naturally chiefly effected by the fore-limbs. The small and large intestines are of equal length, and each is rather more than six times the length of the caecum; in these measurements the present genus differs from the next.

Georhychus.--Of this African genus there are about ten species. The claws are not so long as in the last genus, but there are, as in Bathyergus, four molar teeth on each half of each jaw. The intestinal measurements in an example of G. capensis were: small intestine, 25 inches; caecum, 4 inches; large intestine, 15 inches.

The genus Myoscalops or Heliphohius (also with an African range) has six back teeth on each side. A number of species sometimes referred to the last genus are placed here by Mr. Thomas. The claws are small.

One of the most remarkable genera of this family is the little Heterocephalus from Abyssinia and Somaliland. As Mr. Thomas justly remarks, it "is a peculiar-looking little creature, about the size of the Common Mouse, but looking almost more like a tiny hairless puppy on account of its nearly naked skin, small eyes, and peculiar physiognomy." Though apparently naked, there are numerous scattered hairs over the entire body, and the toes are fringed with stiffish hairs, which must be advantageous to a burrowing animal. There are two species, H. glaber (originally described by Rueppell), and H. phillipsii, of which our knowledge is due to Mr. Thomas. The length of the entire creature including the tail is not more than 134 mm., both species being approximately of the same dimensions. Mr. Lort Phillips, the discoverer of the species which bears his name, writes "that this little creature, called 'Farumfer' by the Somali, throws up in places groups of miniature craters, which exactly resemble volcanoes in active eruption. When the little beasts were at {482} work, I used frequently to watch them, and found that the loose earth from their excavations was brought to the bottom of the crater, and sent with great force into the air in a succession of rapid jerks, and that they themselves never ventured forth from the shelter of the burrows."

FAM. 4. SPALACIDAE.--"The Spalacidae," observes Dr. Blanford, "are sometimes called rodent moles, and resemble a mole in general aspect, having cylindrical bodies, short limbs, small eyes and ears, large claws, and a short or rudimentary tail." The existence of a spiral valve in the caecum may perhaps characterise this family; but it has at present only been found in the two genera Spalax and Rhizomys.

Spalax has inconspicuous eyes and external ears. The tail is totally absent. The lower incisors are more developed than in other Rodents; they project in a bony sheath beyond the posterior end of the ramus of the lower jaw. The scapula is long and narrow. The large intestine is half the length of the small intestine. The animal seems to have only two pairs of teats, one pectoral the other inguinal.

Spalax typhlus of Egypt, which is probably not different from the European form, makes extensive burrows, some of the branches being even 30 to 40 yards in length. In a "domical chamber," situated along the course of one of these burrows, Dr. Anderson found no less than 68 bulbs stored up. Its eyes are mere black specks among the muscles, but they appear, however, to have a proper organisation. There are altogether eight species of the genus, which is entirely Palaearctic in its range.

The genus Rhizomys, including a number of species known as Bamboo Rats, is purely Oriental in range. Rh. sumatrensis reaches a length of 19 inches; the better-known species, Rh. badius, is at most only 9 inches in length--in both cases the measurements are exclusive of the tail, which is a quarter to one-third of the length of the body, and is not scaly but nearly naked, with a few scattered hairs. The molars are three, and the incisors usually orange in colour; but sometimes the upper incisors are white as in Rh. badius. There are thirteen dorsal vertebrae. In Rh. pruinosus the large intestine is considerably longer than the small intestine; the lengths of the two sections of the gut are 42 and 30 inches respectively. In another {483} species the large intestine is slightly shorter than the small intestine. In Rh. badius the two parts of the gut are almost exactly equal in length. There are three pairs of inguinal and two pairs of pectoral teats. The name Rhizomys appears to have been given to the animals of this genus for the reason that they feed largely on roots. They burrow, and, like many other burrowing animals, feed in the evening. As is the case with other forms, Rhizomys is said to burrow with the assistance of its teeth as well as of its claws.

FIG. 237.--Bamboo Rat. Rhizomys badius. x 1/4.

Tachyoryctes is 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 genus Geomys contains 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. {484}

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 genus Heteromys extends into South America.

The genus Dipodomys, with twelve species, is of a Jerboa-like form, as the following measurements of an example of D. merriami will 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.

In Perodipus the 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.

Perognathus is 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 of Perodipus are as in Geomys. The two remaining genera of the family are Heteromys and Microdipodops.

FIG. 238.--Jerboa. Dipus hirtipes. x 1/3. 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 to Dipodomys (hence the name of the latter) and to some other members of the American family Heteromyidae {485} There 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.--Bones of right pes of Jerboa, Dipus aegyptius. x 3/4. a, Astragalus; c, calcaneum; c^2, middle cuneiform; c^3, outer cuneiform; cb, cuboid; n, navicular; I-IV, first to fourth toes. (From Flower's Osteology.)

The typical genus Dipus is 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. In D. hirtipes the body and tail measure respectively 4-1/2 and 7 inches. The hind-feet have a tuft of long hairs below. Mr. W. L. Sclater's newly-founded genus Euchoreutes is somewhat more primitive in its characters than is Dipus. 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 in Dipus, are here smooth, as in Alactaga. The species was probably obtained "in the sandy plains round the city of Yarkand." {486}

Alactaga is much like Euchoreutes; 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 from Euchoreutes by 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 both Dipus and Euchoreutes. 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. In A. decumana the 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. Sminthus is at the opposite extreme to Dipus. 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 genus Pedetes contains 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 in Dipus the 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 be {487} absent, 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.