The changes in the conformation of the cranial portion of the skull, which distinguish the domesticated races of the dog from those which have been less modified by the On fluence of man, partly consist in the obli teration of the sagittal crest, which rises up on the line of junction of the parietal bones, and of its continuation on the occipital bone. In the large deer-hound, we are assured by Prof. Owen, these cristm are as strongly developed as in the wolf; whilst in the smaller spaniel or pug, they are entirely wanting, the cranial dome being smooth and round. But " such modifications," as Prof. Owen remarks, " are unaccompanied by any change in the connections, that is in the dis position of the sutures, of the cranial bones ; they are chiefly due to arrests of develop ment, — to retention of more or less of the character of immaturity ; even the large pro portional size of the brain in the smaller va rieties of house-dog, is in a great degree due to the rapid acquisition by the cerebral organ of its specific size, agreeably with the general law of its development, but which is attended in the varieties cited by an arrest of the gene ral growth of its body, as well as of the par ticular developments of the skull in relation to the muscles of the jaws." Such an altera tion is considered by this eminent anatomist as fairly referable to the influence of domes tication ; since, as he remarks, " no other domestic animal manifests so great a range of variety in regard to general size, to the colour and character of the hair, and to the form of the head, as it is affected by different propor tions of cranium and face, and by the inter muscular crests superadded to the cranial parietes." " Yet under the extremest mask of variety so superinduced," he continues, " the naturalist detects in the dental formula, and in the construction of the cranium, the un mistakable generic and specific characters of the Canis familialis."* Generally speaking, the cranial cavity of the domesticated dogs is relatively increased in capacity ; the facial por tion, on the other hand, is oftener shortened. The skull of the Australian dingo differs but little from that of a wolf. In both, the arch formed by the temporal and parietal bones is much depressed, so that the cranial cavity is small, and the head fiat. The Danish dog and the mastiff resemble the dingo in the shape of their heads, and display as little of intellect or sagacity. The terrier and the hound have the parietal bones more arched, and, consequently, possess a larger cranial cavity. The greyhound has a longer muzzle, and smaller frontal sinuses than the hound ; and the nasal cavity, though elongated, is much contracted, especially at its upper part, so that the sense of smell is less acute in this breed than in most others. The shep herd's dog, which Buffon very erroneously considered as the breed least modified by domestication, is distinguished by its remark ably capacious cranium ; the temporal bones not beginning to arch over the cavity, until they have risen perpendicularly to half their height. In the spaniel and Newfoundland dog, the capacity of the cranium is yet greater than in the preceding ; and they are also dis tinguished by the remarkable size of their frontal sinuses, which causes the forehead to rise almost perpendicularly from the nasal bones. The bull-dog, on the other hand, is distinguished by the shortness and extraordi nary breadth of its muzzle ; while its cranium is less capacious than that of the shepherd's dog. The varieties in general conformation are not less remarkable than those in cranial configuration. Thus, the relative length of the tail is subject to great variation, even the number of its vertebra; differing so widely as from 16 to 21. Some races have an addi tional claw on the hind foot ; and many have an additional false molar on one or both sides. The nature of the hairy covering, too, varies in regard to its closeness or scantiness, its length, its colour, the fineness or coarseness of its texture, &c. &c. ; so that, as M. Fred. Cuvier remarks, the dog-kind presents all the varieties, in respect to the nature of the hairy covering of the body, that are to be found in the entire class of Manimalia. The form of the ears, too, is another marked feature of distinction ; these organs being short and erect in some, long and pendulous in others. The differences in habit and psychical cha racter, also, are almost as characteristic as those of form. The greater number of dogs track their prey by scent ; and this quality may be developed by care in breeding*, so that it attains its greatest excellence in the highest-bred fox-hounds, blood-hounds, and pointers. But the greyhound hunts almost solely by sight ; and, in breeding it, every care is taken to obtain swiftness and "wind," and power of enduring sudden and violent bursts of exertion. In the degree and nature of their attachment to man, again, which is the most marked psychical feature common to them all, we observe a very striking diversity. Perhaps the bull-dog is, of all the domestic ated races, that which is least prone to seek the society of man ; yet, notwithstanding its obsti nacy and ferocity, it does form attachments to human beings, and especially to those whose savage nature is most akin to its own. On the other hand, the pug, which seems like a dwarf variety of the bull-dog, is remarkably timid ; and, though possessing but little sagacity, is tolerably good tempered. The mastiff, again,
possesses the determined courage of the bull dog, but is greatly influenced by kindness, and shows a generous and intelligent nature. The setter, with a considerable degree of sagacity and intelligence, is remarkable for its affectionate and grateful nature, for its docility, and for its humble and anxious solicitude to please. Of all the races of dogs, the spaniel is the one most distinguished for attachment to man ; the most timid, fond, and affec tionate; the most patient under ill treatment : it is, however, by no means distinguished for courage ; and though very docile, is not re markable for native sagacity. It is perhaps in the shepherd's dog that the attribute of intelligence is most strikingly displayed, in combination with courage, fidelity, and per severance : he lives in habits of constant familiarity with his master, learns to interpret his looks and words with an intuitive com prehension, and allows no difficulty or danger to prevent him from carrying his directions into effect. The Newfoundland dog, perhaps, combines more than any other breed the qualities which render the race most generally serviceable to man ; although this combination is not such as fits him for any of those special uses, to which other breeds are particularly adapted.
Now these differences are far greater than those which exist among the acknowledged species of the feline race* ; and therefore, at first sight, might be considered as amply jus tifying the erection of specific distinctions among the several breeds of the canine. But the endeavour to do so would be attended with insuperable difficulties ; for, in the first place, it has been shown by M. Fred. Cuviert, who has paid particular attention to this question, that if we assume the varieties to be permanent races, or originally distinct species, and predetermine that these races are susceptible of few or no modifications, it will be requisite to institute at least fifty diferent species of dogs, all distinguished from each other by recognisable characters,— a hypo thesis which cannot for a moment be enter tained. Moreover, every one who has much intercourse with the canine races becomes im pressed with the feeling, that, notwithstanding the diversities of the greyhound and the bull dog, the blood-hound and the spaniel, the Newfoundland and the terrier, they are all dogs ; and there is obviously an instinctive recognition of this fact among the animals themselves, as is seen by the readiness in which the individuals of the most dissimilar breeds will fraternise together. Further, as already remarked, there is a marked ab sence of tendency to variation in the cha racters of the feline races, the limits of each species being defined by the preservation of its characters through successive genera tions and under all circumstances ; the only exception to this general statement, being in the case of the domestic cat, which, like the dog, passes into numerous varieties, none of which, however, show an approximation to the characters of any other species. Hence, notwithstanding the extent of variation pre sented among dogs, the characters of the breeds do not bear a specific value ; for an amount of variation may be seen among the successive generations'of the same breed, how ever pure it may be kept, or even among the offspring of the same litter, quite sufficient to show that a strong capacity for modification exists in this species. It would not be diffi cult, moreover, to bring together a series of individuals, that should connect the most ex treme forms by imperceptible gradations ; all the different races breed together with the most complete freedom ; and, as already re marked, there is a continual tendency amongst them, if they escape from the influence of man, and intermingle unrestrainedly in a state approaching to their original wildness, to a return to one uniform type of configuration and of hue. Further, whatever their other differences in psychical character, we find that they all agree in that tendency to association with man, which is pretty obviously the chief source of those diversities ; the most impor tant departures from the natural habits of a wild race, being those which have been im pressed upon the several breeds by a long course of training, whose influence has been transmitted, to a certain extent, from one generation to another. We have seen that, in particular races of dogs existing in a half wild state, the force of circumstances, without any human intervention, has developed a new instinct, which has become hereditary within a few generations ; and there can be no diffi culty in understanding, therefore, that the psychical as well as the physical characters of the dog may have undergone a far more marked alteration, in the prolonged period during which he has been under the influence of man. However considerable, then, are the anatomical and psychological differences of the most diverse breeds, these are perpetuated only by the agency of man, and tend to merge themselves in a common type as soon as this is withdrawn ; and through all these changes, the physiological conformity, as marked especially by the generative function, is constantly preserved. And thus it may be unhesitatingly asserted, that there is no such clear and well-marked natural distinction be tween the several breeds of dogs, as can serve to justify the assignment of a separate parent age to any of them.