INTEGUDIENTARY SYSTEM. - Under this head we proceed to indicate very briefly certain peculiarities of the hair, and more particularly the elastic cushion of the sole of the foot, and the remarkable protuberances situated on the back of the Camel.
While the growth and condition of the cuti cular layer of the skin in the different classes of ruminants is of the highest importance in an economic point of view, it is not the less certain that the phases of development through which the integumentary covering passes — its varied aspect and periodicity of renewal, together with the causes which in duce such changes — are matters of high in terest to the physiologist.
In no group of mammiferous quadrupeds have we a more striking, example of the adaptation of structure to the exigences of the creature than obtains in the remarkable dorsal melidm, as in the Horse, rising from the ternal condyle and inferior fourth of the hu nump, and in the cushion-like sole-pad of the Dromedary.
The hump consists essentially of adipose inatter, developed in the subcutaneous areolar substance, its secreting cells having undergone an extraordinary local increase. To support such a mass, the connecting tissue exhibits a corresponding augmentation, the fibres assum ing the character of ligamentous bands, which are firmly united below to the capitals of the bony columns of the dorsal vertebrm. In reference to the function of this growth tra vellers have ascertained beyond all contro versy that it serves as a store-house of nourishment, affording to the animal, in con junction with the stomachal water-cells, a pro vision against the inanition which long jour neys would otherwise entail. In accord with this statement, it has been observed that the hump of the Dromedary becomes attenuated and reduced under circumstances of impover ishment, while, on the contrary, it is marked by rapid increase and ultiniate plumpness when the supply of food is abundant.
The general character of the dermal en velope in Camelidx deserves little comment ; the hair is coarse and shaggy in the typical species, and of a soft woolly texture in the Auchenias, where it is also very long. At certain points it acquires in the Camel a rigid bristle-like character, this being especially manifest at the under part of the feet, near the margin. In this spot, however, the hairs are scanty, and they are entirely absent for a small space, over the so-called knees, and at the under and fore-part of the chest, where frorn constant pressure during the recumbent posture of the body, the cuticle acquires a horny consistency. These callosities are not present in the Llama.
One of the most interesting anatomical features, forming a distinction between the two cameline genera, consists in the degree of organisation of the foot-pad and corneous in vestment of the toes. In the Camels, properly so called, the digits are more or less com pletely imbedded in the broad elastic cushion which extends for a considerable distance laterally on either side of the foot, binding and fixing the phalanges immoveably together ; while at the same time it is particularly worthy of remark, that the hoofs are merely repre sented by two rudimentary nails situated on the dorsal surface of the tip of each toe. In the Llamas the sole-pad is double and narrow, each division being limited to one side of the cloven foot, while the nails, instead of being weak, are very powerfully developed, and strongly curved. In consequence, therefore, of the easy separation of the toes, combined with the modifications of the pad and hoof here referred to, it is at once evident that such a condition of the foot is peculiarly adapted to an animal whose life is destined to be spent, unlike that of his more highly valued congener, on the rugged slopes and precipices of a mountainous district.
In the solid-horned Ruminantia very im portant changes coexist with the shedding of the antlers. These organs occupied our at tention when describing the anatomical rela tions and development of the horns ; but, as some physiologists are disposed to regard them as part of the dermo-skeleton, we take this opportunity of reverting to the subject. If such a view as the one here mentioned be not supported by the mode of growth, it ac quires nevertheless an appearance of consist ency when we bear in mind that the annual shedding of the horns takes place contem poraneously with that of the hair. By others, this simultaneous loss of structure is regarded as a mere coincidence, affording no proof, they say, of the integumentary character of the cranial outgrowths, but rather indicating a special provision, for the explanation of which we are to look to another source. This ar gument is followed up by assuming that, were it not for the change alluded to, the young Deer would sustain injury from the bucks, which, at the period of the full evolution of the antlers, exhibit a destructive and relentless ferocity. After the loss of the offensive wea pons, it is well known that their disposition acquires a milder habit. In furtherance of this view of the question we are likewise re minded that it is necessary to associate the persistency of the horns of the Giraffe with the equally well ascertained fact, that in this aberrant cervine genus, there is, as in Cervidm proper, a periodical desquammation of the cuticle not affecting the hairy covering of the cranial epiphyses, and involving no subsequent alteration in the animal's psychical character, which, under ordinary influences, is proverbially gentle, and always the same.
In a former part of this article, reference has been made to the epidermic nature of the corneous investment of the bony cores in cavicornua, and the extension of it found pro longed over the frontal region in the Buffaloes, a tribe exhibiting an approach to the Pachy dermata in many respects, and more especially in the organisation of the hide, which has a leathery consistence, and is scantily provided with stiff bristly hair.
In conclusion we may remark that the cloven condition of the hoof in the typical ruminant is evidently designed to impart light ness and elasticity to the spring ; and, in order to give full effect to such an arrangement, many species are provided with a special glandular sebaceous follicle between the toes, whose office is to furnish a lubricating secre tion, calculated to prevent injury from friction of the digits one against the other. Fog. 351. represents the position and dimensions of this organ in the Sheep. According to Sir Charles Bell there is yet another intention in this cloven form, viz., that of aiding the voluntary eleva tion of the foot when it has sunk deeply into soft ground. " We may observe," he says, " how much more easily the Cow withdraws her foot from the yielding margin of a river, than the Horse. The round and concave form of the Horse's foot is attended with a vacuum or suction as it is withdrawn ; while the split and conical shaped hoof expands in sinking, and is easily extricated."#