PART IV. NATURAL HISTORY OF THE PRINCIPAL ANIMALS USED BY MAN IN RURAL SPORTS. BOOK L-COMPARATIVE ANATOMY OF MAN, THE HORSE, AND DOG. CHAP. I. GENERAL VIEW OF THE DIVISION, SECT. 2.-THE NERVOUS SYSTEM. SECT. 1-THEIR POSITION IN THE SCALE ever, it is much more developed in those OF CREATION. 1. MAN himself, together with the horse and the dog, and even the hawk and the decoy-duck, which are the only animals used by him in the capture of the objects of his sport, are all included under the general division VERTEBRATA. These are distinguished by the possession of an articulated skeleton within their bodies, and by a vertebral column, containing the most Important parts of their nervous system. With the exception of the birds, all the others are included in the class MAMMALIA, so named because they give suck to their young by means of the mamma. The three species, however, are widely separated in the division, man taking the head of all in a distinct subdivision, and separated from the CARNIVORA, among which the dog is included, by the apes and monkeys. Between the dog, again, and the horse, there intervene the whole of the cetaceous animals and the glires; the horse belonging to the lowest tribe of the mammalia, namely, the UNGULATA, or those having hoofs. Between these three there will be found to be considerable points of difference in each of the systems of which their frames are composed; all three, however, have a skeleton consisting of the same materials, and containing within its cavities a nervous, a circulatory, a respiratory, a digestive, and a reproductive system. All have the same organs of sense, though differently endowed; and in all the parts of the skeleton are connected together by ligaments forming joints, and moved upon each other by muscles of various forms. The chief differences are-first, in the volume and form of the brain; secondly, in the nature and form of the stomach and intestines; and, thirdly, in the form of the organs of locoinotion. parts upon which the extent and powers of spinal cord, although these also send their nerves to them. Thus, the most important organs of all have their separate supplies, by which provision is made against accident; and, in case of its occurrence, one part being enabled to do duty for two. In this way the whole nervous system is divided into first, the brain; secondly, the medulla oblongata and spinal cord; thirdly, the general nerves of motion and sensation; fourthly, the special nerves of respiration; fifthly, the nerves of the viscera, commonly called the sympathetic system; and, sixthly, the special nerves of the senses derived from the brain itself. In all these animals the nervous system consists of two parts; the grey, in which power is generated, and the white, through which it is transmitted. The grey constitutes the greater part of the exterior of the brain and the interior of the spinal column, whilst the white makes up the interior and central parts of the brain, the exterior of the spinal cord, and the bulk of the nerves of the body. 3. THE VARIATIONS in these several parts are the following:-In man the brain is much the most voluminous, especially in the anterior part, which is the chief organ of the mind. Here the grey matter is very much convoluted, and thereby rendered more extensive in quantity and in surface, by which his general mental powers are augmented. Next to him in this respect comes the dog, who has sometimes tolerably deep fissures in his brain, and consequently a more extended surface than usual; but in all cases much more so than in the horse, whose brain is, as compared to his whole body, very much less than the dog's, and still more diminished in proportion as compared to that of man. In the dog, however, and especially in those whose powers of smelling are much developed, the anterior lobes, in which the nerves of smelling take their rise, are largely increased in size, and nearly as much so in the horse, who, like all animals dependent upon this sense for their safety in selecting food, has considerable acuteness of smell. In other respects the nervous systems of the three are closely allied, and the description which will serve for the one will also suit the others, except in the minute detail of parts. SECT. 3.-THE SKELETON. 4. In all three the skeleton consists of the same parts, though the bones composing them vary in number, and to some extent in form. (See skeleton of Man, Dog, and Horse, figs. 1, 2, and 3, in which the letters attached to fig. 1 apply also to the corresponding parts in figs. 2 and 3) It is divided into two portions one forming cavities for containing the vital organs and protecting them from danger: and the other consisting of central supports adapted to the purposes of locomotion, by offering levers to be worked by the various muscles. The bony cavities arefirst, the cranium and spinal column; secondly, the thorax or chest, attached to the middle of the spine; and thirdly, the pelvis, terminating it. The bony organs of locomotion are the four extremities of the body. 5. THE CRANIUM OR SKULL, is variously formed in the three species under consideration; but it consists in all three of the same number of bones, eleven of which combine together to form a hollow case for the brain, whilst six of these eleven, together with the upper and lower jaw-bones, the bones of the nose, and the cheek-bones, constitute the face. In this part they are developed into several cavities, two of which are called the orbits, and contain the eyes; two, close together, form the nostrils; one between the upper and lower jaw-bones, the mouth; and one on each side for the ears, which last part also contains four little delicate bones for communicating the vibrations of the air to the nerve of hearing. In the jaws, also, there are fixed two rows of teeth, the upper and the under, which vary considerably; but in each there are three kinds-viz.: first, the incisors, being more or less cutting nippers, and placed in front; secondly, the canine, pointed, and intended for holding or tearing; and thirdly, the molars, for grinding The formula, as it is called, for each, is as follows: be ascertained by the teeth, but that of the The age of man and of the dog can seldom horse may generally be arrived at with tolerable certainty, as follows: MARKS OF THE AGE OF THE HORSE AS SHOWN BY THE TEETH. At one year old, all the milk-teeth are come up; the two centre nippers of the lower jaw are partially worn down, the two next very slightly so, and the outside nippers entire. At two years old, the "mark" is nearly obliterated in the four centre nippers, and those of the outside ones are much reduced in size. |