tunnels, would be

inconvenienced by such unchangeable disposition of their fur. Accordingly in Moles, Shrews, and Platypi, e.g., the stem of the hair is filamentary, the end broad and flat, and the slender and expanded parts may alternate twice or oftener in the course of the hair, enabling the whole fur to assume any direction in which it may be stroked.

The heat-retaining property of the pilose covering is mainly due to the amount of air it is able to retain. The long curly character of the Sheep's and Llama's fleece is one modification to this end; the swifter Deer and Antelope are not so encumbered; but the hairs composing their thin but close and smooth pelt have a cellular structure which combines lightness with the requisite air-intercepting quality.

In the Horse there is a central point on each flank, whence the hair radiates in a somewhat spiral manner: the corresponding centre in the Giraffe is a little behind the middle of the abdomen, towards the lower part.'

The hide of the larger Ruminants which are exposed to the elements in the prolonged act of grazing is defended by the greasiness of the hair, as may be felt in the recently killed Reddeer or Fallow-deer. The amount of sebaceous matter excreted with the hair in some Antelopes is such as to have suggested a specific name in accordance therewith.2

The varieties of structure of hair are extreme: those of Deer seem almost wholly to consist of cellular pith, the cortex undefinable: the tail-hair of the Horse, and the Pig's bristle, offer the opposite extreme of thickness of cortex and minimum of pith. But these and other modifications demand a special micrography.3 Hairs of some quadrupeds, the Racoon, e. g., in the filamentary productions of the cortical scales, recall the character of the immature down in Birds (vol. ii. p. 237). In some Rodents, the Hare, e. g., several fine hairs project from the mouth of the same sheath as the larger hair. In Mice and Shrews the margins of the cortical scales encompass the hair and project forward or rootward. This free projection is such in some bats that the hair presents the appearance of a succession of ensheathed funnels with their apices backward or outward. The hair of the Sloth is fluted, the crust appearing to be composed of several

The varieties in this respect merit more notice than they have hitherto received. 2 Laurillard's Antilope unctuosa is probably the same species as Kobus Sing-sing of Ogilby.

Brief immersion in sulphuric acid and cleansing with ether are requisite preliminaries for clear and satisfactory microscopic specimens of hairs.

filaments confluent with a common central pith. In the Peccari the pith of the coarse body-hair is crossed by condensed cells like beams strengthening the cortex. The colour of the hair is lost by age in Man, and during the winter season in the annually renewed covering of many arctic Mammals: the endosmotic transfer of their contents from cell to cell of the pith effects this change. The hairs of the Cape-Mole are peculiar for the iridescent tints they reflect, whence its generic name, Chryso

chloris.

6

The stiffer, thicker kinds of hair' are called bristles:' when these attain unusual length, grow from the lips, cheeks, and other parts of the head, and have the matrix supplied by unusually large nerves, endowing them with tactile or exploratory faculties, they are termed 'whiskers' or vibrissæ": those which beset the muzzle of the Walrus attain the thickness and stiffness of spines, and serve, also, mechanical uses.2 The muscles moving vibrissæ have the striped fibre.

a

488

§ 361. Spines.--Over the major part, including the more exposed surfaces, of the skin of the Hedgehogs (Erinaceus, Centetes) spines are developed in such numbers and of such length as to conceal the hairs; they are nearly straight, terminate in a point, and, when fully formed, are smaller at the root than in the shaft. They have a thick, stiff, horny cortex, including a pith of cells arranged in transverse groups, fig. 488, a. The matrix is originally situated beneath the derm, in contact with the strong 'panniculus carnosus;' but section of the skin shows the roots and sheaths of the quills, extending to different depths according to the period of their growth: the newly formed ones are lodged deep, and terminate without contracting, the pulp being large and active, and the cavity containing it of corresponding size; but as the growth of the quill proceeds, the reflected integument forming the sheath gradually shortens and draws the quill nearer the surface; the pulp is at the same time progresxx. vol. iii. p. 245.

1

Section of skin, with spines, of Hedgehog: a, section of spine magn.

2 Ib. p. 246.

sively absorbed, and the base of the quill is contracted in diameter, until it adheres to the surface of the derm by a narrow neck, below which is a slightly expanded remnant of the matrix. The disposition of the dermal muscles subserving the spiny armour of Erinaceus europæus, is given at pp. 18, 19, figs. 7 and 8.

6

In the Porcupine (Hystrix cristata) the spines attain so great a length that they are called quills.' The formative pulp, fig. 489, e, is longitudinally furrowed; to it is due the cellular pith: the capsule or inner layer of the theca is reflected into, or fills, the pulp-grooves, and deposits therein, and continuously around the whole, the horny cortex: the consequent arrangement of crust and pith is such as in transverse section to give the figure, fig. 489. Beneath the matrix is a cavity like a minute' bursa mucosa,' which allows much freedom of motion to the quill when acted upon by the muscle, d, of the sheath, f: a sebaceous gland, h, serves the quill opening into the sheath near the outlet. When the growth is completed, the matrix shrinks, and the same movement to the periphery of the derm takes place as in the spines of the Hedgehog. Thus it happens that when the quills of the Porcupine are violently shaken by the action of the cutaneous muscle, c, the adhesion of some old quills to the derm has been so reduced that they are thrown off.

Section of skin, with matrix and root of quill: i, section of quill, Porcupine.

§ 362. Scales. Only one genus of Mammal (Manis) offers a covering of scales; and with them are associated hairs. The scales are large, epidermal or horny in tissue, and imbricate or overlapping, with the free border turned backward, vol. ii. fig. 158. The external surface of the derm is raised into large rhomboidal processes, upon which the scales are moulded: beneath the derm is a thick panniculus carnosus,' adapted to draw the integument around the animal as a means of defence, and connected with muscular slips, which erect the scales.

A few other Mammals show partial deposits of scale-shaped cuticle. Thus, in the tail of the Beaver the epiderm is disposed in hard scale-like plates, the anterior margins of which project obliquely inwards, and develop small pointed processes which pass into corresponding depressions of the derm. In the great Flying Dormice of Africa (Anomalurus) there is a double row of alternate overlapping horny plates at the under part of the base of the tail, reminding one by their size and strength of the scales of Manis.

§ 363. Nails, Claws, and Hoofs.-The derm covering the ends of the digits, in Man, is closely connected or confluent with the perioste at the back of the last phalanx, and forms near its base a crescentic groove or nail-bed,' from the ridged and highly vascular surface of which a solution of epidermic material exudes, which material formifies as cells, at first vertical to the surface; then, when pushed off by a succeeding precipitate of cells, becoming flattened, and ultimately condensing or coalescing into the horny plate termed the nail.'

In the hoofed quadrupeds the ridged or laminate vascular derm or dermo-perioste extends over the fore and lateral parts of the last phalanx, and similarly provides it with a thick hard horny wall, in great part of which the primitive cells have condensed into fibres perpendicular to the plane by which the superincumbent weight is transferred to the ground. In the Horse the formative lamellæ are shown in fig. 17, at 17; the resulting hoof being turned off to expose the horny lamellæ, ib. 3, which interlock with the vascular lamellæ. From the greater part of the derm covering the under surface of the foot horny matter arranged as vertical fibres is also formed, completing, with the denser front and side walls, the case called hoof.' The fibrous epiderm on the sole of the bisulcate foot of the Ruminant is very thick, but less dense than in the soliped. Further particulars of the structure of the Horse's hoof are given at pp. 39-41.

In Carnivora the base of the last phalanx forms a 'nail-bed' much deeper than in Man, a plate of bone being reflected forward like a sheath for the base of the terminal, prominent, and pointed part of the phalanx. The dermo-perioste of this bed develops a very dense horny sheath covering the claw-core, and reciprocally received at its base within the bed or sheath formed by that part of the ungual phalanx. For the form of such claw' in the Felines, and the muscular and elastic structures connected therewith, see pp. 69, 70, and fig. 36. The maximum of claw-development is, however, presented by the Armadillos (vol. ii. figs. 272, 276), the Sloths (ib. fig. 280), and the Anteaters (ib. fig. 263): in

the gigantic extinct members of the order Bruta (Megatherium, fig. 279, e.g.) the claws and their core or supporting bone rivalled the horns of many Ruminants in bulk.

$364. Horns.-The horn of the Rhinoceros consists of a uniform compact agglutinate mass of epidermal fibres, the slightly concave base of which is attached to the dermo-perioste of as slightly elevated a rugous tract of bone: it is medial in position and symmetrical in shape.

The Asiatic continent and the Island of Java have the onehorned species called Rhinoceros indicus and Rh. sondaicus (vol. ii. p. 284, fig. 165): the same continent and the Island of Sumatra have the two-horned species (Ih. sumatranus): all the known kinds of Rhinoceros, four in number, of Africa are two-horned: in these one horn is behind the other in the same medial tract of the upper part of the skull. The nasal bones support the constant or anterior horn: when a second is superadded it is attached to the frontals, and is, usually, shorter than the first; in Rhinoceros Oswelli considerably shorter; but in Rh. Ketloa it is almost or quite as long as the first horn, but is straight. The horn or horns of the female Rhinoceros are usually shorter or smaller than in the male. In the young one-horned Rhinoceros living, from 1834 to 1849, at the Zoological Gardens, the new fibres of the growing horn were chiefly added to the front and sides, those at the back decaying, and by this direction of addition the horn preserved its relative position to the fore part of the growing head. This local decay and renovation became less conspicuous after the animal had gained its full size; and in the long horns of aged individuals the whole basal circumference presents the same smooth and polished surface, the reception of additional matter being then restricted to the completed area of the base.

Raise and prolong the bone covered by the vascular hornforming tegument, and the next type of horn would result. In most Ruminants (Oxen, Antelopes, Goats, Sheep) a pair of processes extend from the frontal bones, the dermo-perioste of which develops a sheath composed of horny fibres: but the supporting process is long and conical, and the horn which sheaths it is correspondingly hollow, whence the Ruminants, so armed, are termed hollow-horned.' The bone is termed the core:' it has usually a rugous or grooved exterior: in Bovide and Ovide the frontal

The nasals of the fossil Rhinoceros minutus, Cuv., show a transverse pair of small and smooth conical processes, which cannot confidently be inferred to have sustained horns: like the Rhinoceros incisivus, I believe it to have been hornless.

2 There are reports, needing confirmation, of a small third horn, as a rare variety.