The sense of hearing, without attaining in man the perfection which it reaches in certain animals, is nevertheless of great delicacy, and becomes an infinite resource of instruction and pure enjoyment. Not only are differences of intonation, intensity, and timbre recognized by our ear, but the most delicate shades of rhythm and tone, the relations of simultaneous and successive sounds which give the sentiment of melody and harmony, are appreciated, and furnish us with the first and most natural of the arts--music. Let us now pass to the bony portion of the human body, and consider first of all the head. The head is shared by two regions, the cranium and the face. The predominance of either of these regions over the other depends upon the development of the organs which belong to each. The cranium contains the cerebral mass, that is, the seat of the intellect; the face is occupied by the organs appertaining to the principal senses. In animals, the face greatly exceeds the cranium in extent; the reverse is, however, the case with man. It is but rarely that with him the face assumes importance at the expense of the cranium--in other words, that the jaws become elongated, and give to the human face the aspect of a brute. There is in the human face an anatomical characteristic of greater importance than any taken from the elongation of the cranium; that is, the projection forward, or the uprightness of the jaws. The term _prognathism_ (from πρὸ, forward, and γνάθος, jaw) is applied to this jutting forward of the teeth and jaws, and _orthognathism_ (from ὀρθὸς, straight, γηάθς, jaw) to the latter arrangement. It was long admitted that prognathism, or projection of the jaws, was peculiar to the Negro race. But this opinion has been forced to yield to the discovery that projecting jaws exist among people in no way connected with the Negro. In the midst of white populations this characteristic is frequently met with; it is occasionally found among the English, and is by no means rare at Paris, especially among women. Prognathism would appear to be characteristic of a small European race dwelling to the south of the Baltic Sea, the Esthonians, and which itself is but the residue of the _primitive Mongolian_ race. It is probably the mixture of Esthonian blood with that of the inhabitants of Central Europe, which causes the appearance in our large cities of individuals whose faces are prognathous. We can not close our remarks upon the face without speaking of a curious relation between it and the cranium, which has been much abused; we allude to the _facial angle_. By _facial angle_ is meant the angle which results from the union of two lines, one of which touches the forehead, the other of which, drawn from the orifice of the ear, meets the former line at the extremity of the front teeth.