I shall never forget the remark of my greatest and most revered teacher, when he called me into his consultation-room to show me a case of typical locomotor ataxia, gave me a brief but significant history, put the patient through his paces, and asked for a diagnosis. I hesitated, blundered through a number of further unnecessary questions, and finally stumbled upon it. After the patient had left the room, I, feeling rather proud of myself, expected his commendation, but I didn't get it. "My boy," he said, "you are not up to the mark yet. You should be able to recognize a disease like that just as you know the face of an acquaintance on the street." A positive and full-blown diagnosis of this sort can, of course, only be made in two or three cases out of ten. But the method is both logical and scientific, and will give information of priceless value in ninety-nine cases out of a hundred. Probably the first, if not the most important, character that catches the physician's eye when it first falls upon a patient is his expression. This, of course, is a complex of a number of different markings, but chiefly determined by certain lines and alterations of position of the skin of the face, which give to it, as we frequently hear it expressed, an air of cheerfulness or depression, comfort or discomfort, hope or despair. These lines, whether temporary or permanent, are made by the contractions of certain muscles passing from one part of the skin to another or from the underlying bones to the skin. These are known in our anatomical textbooks by the natural but absurd name of "muscles of expression." Their play, it is true, does make up about two-thirds of the wonderful shifting of relations, which makes the human countenance the most expressive thing in the world; but their original business is something totally different. Primarily considered, they are solely for the purpose of opening or closing, contracting or expanding, the different orifices which, as we have seen, appear upon the surface of the face. This naturally throws them into three great groups: those about and controlling the orifice of the alimentary canal, the mouth; those surrounding the joint openings of the air-tube and organ of smell, and those surrounding the eyes.