Thus the general nature of this principle of investiga tion becomes apparent; and in this way, for example, if we only suppose that the teeth are given, all the rest of the structure, within certain limits, follows. The same happens if any bone be assumed ; so that, commencing from any one point, there is a general concatenation which determines all the rest. And thus, in the hands of an ex pert and practised anatomist, may the whole animal be discovered from the examination of any one part.
This general sort of conclusion requires, however, many modifications, when it is applied to use in specific eases ; nor are there many in which the broader principles are sufficient for the required purpose, without that experi ence in the varieties of animal form which can only he derived from observation. These remarks will he more intelligible, if, front carnivorous, we turn our attention to herbivorous animals.
If an animal is found to have a hoof, it is a natural con clusion that it is not carnivorous, because it has no claws for seizing its prey. Having, therefore, no such use for its fore legs, which are, like the hinder ones, merely in tended for support, and not as hands, they are constructed on a principle of less strength. • Hence they have no clavicles, nor any of the forms in the accompanying bones, which would have been necessary had these existed. For similar reasons the scapula: are comparatively narrow. The structure of the fore arm is also such as to allow less freedom of motion, since that, as we just remarked, is not wanted. For this reason the ulna and radius are put to gether in a different manner, and differently jointed, also, with regard to the humerus. In the teeth, very consi derable differences from those of the carnivorous animals are also perceptible. These organs, required to grind wood, or grain, or tough plants, demand irregular and rough, though flat surfaces: and hence the enamel and bony matter are so intermixed, and that in a laminar and vertical direction, that this alternate order of soft and hard parts produces a surface as rough as that of a millstone. From the peculiar motions required for this operation of grinding, it also becomes necessary that the articulations of the jaw should be modified accordingly. Hence the
condyles, instead of being adapted to confined joints, as in the carnivorous tribes, have a different and a flattened form, adapted to corresponding sockets in the temporal bones. And as it is also unnecessary that the muscles of this part should he so strong, the cavities in which they lie are neither equally deep nor of the same forms.
Now, in the same manner as in carnivorous animals, one of these peculiarities serves to indicate the others. Yet in-this department, as the habits of herbivorous animals, and the nature of their food, are very different in different kinds, while their pursuits arc also infinitely varied, it re quires many other inferior kinds of generalization to come to approximations respecting them. This is even the case in the hoofed animals ; among whom, in the different sub divisions, there are peculiarities of general character by which they are distinguished. Thus, for example, if the system of the teeth is less perfect in one than in another, a difference is required in the organs of digestion, and thus it would be expected that such kinds were ruminant; while other peculiarities also follow.
In all these cases, we can see the reasons for the varia tions, and for their mutual dependence, so that we argue with comparative fearlessness respecting the structure of ane part from the examination of another. But there are many of those concatenated forms which are matter of experience rather than of reasoning. Thus, it is only from observation that we know, that in almost every case ruminating animals have cloven hoofs and horns, or, in defect of these, tusks or sharp teeth. Yet the constancy of these is sufficient to show that there is some necessary connection among them, or some particular object in view in thus associating them. Till this is known, we must be content to lay down the general rules from experience merely, and by taking a range sufficiently wide, that may he rendered perfectly available. Thus, the mere circum stance of a cloven hoof may determine not only the gene ral forms of the teeth, but those of the jaws, and, by con sequence, of the vertebrae, the shoulders, and so on, throughout the whole body.