lobulated. In the human kidney the tubuli are grouped into from twelve to fifteen conical bundles, the apices of which project

483

into a common pelvis; but
occasionally
two cones
combine to terminate by a
common mammilla: in fig.
483 are shown three cones,
in section, with the rela-
tive position thereto of the
arteries, a, and the veins,
b. In the foetus the cor-
tical part is subdivided
like the medullary, but the
clefts become obliterated in
the growth of the kidney.

Quadrumana have a single mammilla; but in the larger kinds it is extended, and the tubuli are partially

grouped into bundles near the cortical substance. The kidney in

484

the Suricate, Viverridæ, Hyænas, and Felines is chiefly remarkable for the arborescent disposition of the veins on or near the surface; the mammilla is single, as it is, also, in the Mustelide, Canide, and Suburside. In Bears, Seals, and Whales, the kidney is divided into numerous lobes or renules, in the Walrus amounting to three or four hundred, and in the Porpoise, fig. 427, E, to even a greater number. Each renule has its own capsule, which is removed at a, a, fig. 484; a section of

the renule shows it to be composed of a cortical and medullary

substance, ib. b, c; the tubuli terminate at the apex of a mammilla, d, which projects into an infundibulum. The infundibula are prolonged, and unite to form the ureter which comes out at the medial and hinder surface of the kidney and enters the neck of the urinary bladder.

485

In most quadrupeds this reservoir is more pendulous, has a more complete covering of peritoneum, than in Man. The oblique valvular course of the ureters through its coats is common to the Mammalian class. The monotremes are the sole exceptions; in them the ureters, fig. 485, 1, 2, do not terminate in the bladder, k, but in the urogenital canal, c, the orifice of the spermduct or oviduct, m, intervening between that of the ureter and the bladder. The urine may dribble out with the fæces, or may pass by a retrograde course into the bladder; but, in either case, it is expelled per cloacam not per urethram: the penis in the male subserving the conveyance of the semen only. In all other mammals both urine and semen are carried out by the urethral canal in the male; and, in some Insectivora (Shrews, Moles) and Quadrumana (Slow Lemurs), the clitoris in the female is similarly traversed by a canal, which here, however, is exclusively for the urine. The vaginal orifice intervenes between the prominent and perforate clitoris, figs. 485, 546, c, and the anus.

Clitoris, vagina and vent, Shrew.

CHAPTER XXXV.

TEGUMENTARY SYSTEM AND APPENDAGES OF MAMMALIA.

$357. Derm.-The main constituent of the skin of Mammals consists of an interlacement of fibres of the white or sclerous kind, fig. 486, f, continuous with those of the subjacent areolar tissue, i, but more or less abruptly defining a firm sheet of strong and tough fasciculate framework investing the body: the looser central or initial texture, i, includes, in its larger meshes, fat, sweat-glands, h, bulbs of hair, of bristles, or of spines, with sebaceous follicles, according to the species: it is traversed by the nerves of the sensitive or tactile papillæ, d, by sweat-ducts and by arteries, veins, and absorbents: it is covered by the epiderm, c, a. With the sclerous fibres of the derm are blended a varying proportion of the yellow elastic fibres, and of unstriped muscular tissue, especially in relation to the roots of the hairs or spines.

The texture of the derm is firmest at its periphery, where its surface is best defined: its thickness varies in relation to the bulk of the species and to other circumstances; it is such, e.g., in certain Perissodactyles and the Hippopotamus, as to have suggested the name of Pachyderm for an artificial group of Ungulates in the Cuvierian system. In the full-grown Giraffe the corium hardly exceeds half an inch in thickness at any part: in the Indian Rhinoceros, of about the same weight, the average thickness of the derm is between two and three inches: it is thinner on the less exposed surfaces and at the bending of the joints. In the large specimen which I dissected the integument on the middle line of the abdomen presented a general thickness of threefourths of an inch on the inner side of the extremities, it was about one-fourth of an inch in thickness. It was connected to the abdominal parietes by a loose cellular tissue, and by a closer one to most of the other parts of the body; but the parts to which the stiff and ponderous hide most firmly adhered were the spinous processes of the posterior lumbar and sacral vertebræ, and the anterior extremities of the iliac bones, at which places the corium was blended with the periosteum, and was thin. The derm adhered over the jugal bones to a kind of movable

fibro-cartilage; but its attachment along the median line of the fore part of the head was so firm as to require, especially beneath the horn, the use of a chisel in order to separate it from the skull. Besides its attachment to subcutaneous cellular substance, fasciæ, elastic tissue, fibro-cartilages, and periosteum, the derm is connected with parts which are destined for its motions and adjustment upon the body. The 'panniculus carnosus' of the Rhinoceros is developed in certain parts to an extraordinary thickness; the permanent folds in the hide of the Indian species serving to afford, like the processes of bone, a firmer insertion to the aponeuroses of the cutaneous muscles than a plane surface of integument could have done. A sheet of these muscles situated on each side of the thoracic or scapular region sends its fascia into the interstice of the fold in front of the anterior extremities, the skin being bent upon itself, as it were, to grasp this fascia. Similar portions of panniculus carnosus send their aponeuroses into the posterior folds of the skin.

The derm, in Cetacea, is a somewhat gradual condensation of the close fibrous reticulation in the areola of which the oil is contained; the thickness of such subcutaneous tissue, called blubber,' being enormous in the large Whales: it is wanting at the fins, and here the derm is closely connected with the sclerous tissue covering the bony framework of the pectorals, and contributing mainly to form the dorsal and caudal fins: in the latter the subdermal fibres become assorted into three layers, the upper and under ones being longitudinal, the intermediate layer transverse, and the texture of the whole so compact that the traversing veins as well as the arteries preserve their open state when cut across. The fine lengthened papillæ or villi from the periphery of the derm are noticed at p. 188.

Certain Rodentia contrast with the Pachyderms in the thinness and lacerability of their derm, resembling birds in that respect. Another Lissencephalous family reproduces a crocodilian character, in the development of osseous scutes upon the peripheral part of the derm (vol. ii. p. 396, fig. 261). These scutes are small, mostly quadrilateral, and suturally united so as to form three principal groups: one protecting the trunk like an arched roof, a second forming a flatter shield or helm upon the head, the third encasing the tail, like a sheath. In most existing Armadillos the trunk-armour consists of an anterior thoracic buckler in which the ossicles form a kind of mosaic work; a middle annular' part in which they are disposed in transverse series movable upon each other; and a posterior lumbar buckler, like the thoracic

one by this modification of the dermal plates the little animal is enabled to roll itself into a ball, and protect its snout and legs beneath the trunk-armour. In the large extinct Armadillos (Glyptodon) the annular or banded modification of the armour was not present; and the whole of the dermal scutes of the trunk were united into one massive domed roof: the marginal scutes being generally triangular, the rest more or less regularly hexagonal. The inner surface of the scutes, imbedded in the derm, is smooth; the outer surface coated with epiderm is sculptured in a definite pattern, distinct for each species and characteristic thereof. The dermal plates of the caudal sheath in certain kinds of Glyptodon formed annular series of large conical tubercles : the first ring, in all, was distinct from the rest of the caudal sheath, to facilitate the movements of the tail.

In the Pangolins (Manis) the exterior of the derm is grooved, as in Lizards, for the lodgment of the bases of the large horny scales, which protect the body and tail by their imbricated overlapping arrangement (vol. ii. fig. 158). The muscular tissue enters in greater proportion than usual into the composition of the derm of this Mammal, in connection with the thick panniculus carnosus,' and in relation to the erection of the scales, when the integument is drawn defensively about the uprolled trunk and tail. Productions or duplications of the derm, with included muscles, &c., form the peculiar mammalian oral appendages called lips: an everted fold of skin forms the scrotum:' an inverted fold the marsupium and the cheek-pouch (p. 386, fig. 300): the derm is extended between the digits to form the web' in most aquatic quadrupeds, and also beyond the digits to augment the swimming surface in the Ornithorhynchus: a duplicature of integument forms the dewlap' in certain Bovines: it forms a broad fold on each side, continued from the fore to the hind limbs to form the parachute, in the Petaurists, Pteromyds (Vol. ii. fig. 156), and Flying Dormice (Anomalurus): in the Colugos (Galeopithecus) the dermal fold expands from the nape to the fore-feet, from these to the hind-feet, and thence to the tip of the tail, forming a triangular interfemoral' flap. But the most extraordinary developments of derm are presented by the Bat tribe (vol. ii. p. 278, fig. 156): the antibrachial fold' crosses the deep interspace between the humerus and radius; the digital fold,' which mainly forms the wing, occupies the interspaces of the long and attenuated digits; the flank-folds' extend from the fifth digit to the tarsus; the interfemoral fold' passes from leg to leg, intercepting more or less of the tail.