Leonardo da Vinci, who was certainly one of the greatest connoisseurs of the human countenance, had studied its anatomy with such ardour that the drawings of his preparations still excite the admiration of the learned by the accuracy of the most minute details. '_First study Science, and then follow her daughter Art_’, said Leonardo to his pupils; and these words are worthy of him who was not only a great artist and mathematician, and an illustrious philosopher, but who earned the title, far more difficult to acquire, of being an innovator in science, and one of the founders of the experimental method. We must not begin the study of the face with that of the human anatomy. The web of muscles is so close, the direction of the fibres so intricate, that we are baffled unless we know the origin of these muscles in the lower animals, unless we investigate their office in simpler beings, and the modifications which they undergo on the zoological ladder. The most important parts of the face are the apertures of the mouth and nostrils. These alone never disappear, however the form of the head may alter in different animals. The lips, nose, and chin may become unrecognisable, as in birds; the eye may become a mere point, as in the mole, or may disappear altogether as in certain animals living in caves; but the mouth always remains, because the alimentary canal is the most useful organ of the body. It appears even in animals that have neither heart nor lungs, and is formed like a funnel at its upper end. It is this end of the alimentary canal which we call the face. However grotesque such a mode of expression may seem, it is yet the expression of truth. The development of the facial muscles is proportioned to the need of seizing prey and crushing the food. In frogs, fish, reptiles, birds, that swallow their food whole, one may say that the face is wanting; they have no expression except in the eye. In birds, the functions of the facial nerve are restricted to a little filament distributed to the cutaneous muscles of the neck, which produces that ruffling of the feathers and erection of the crest which is the characteristic expression of their feelings. The more complex the movements of seizing and devouring the prey become, the more complicated becomes the formation of the mouth. The lips must be mobile in order to suck the nipple of the breast, in the manner of a cupping-glass. Later, they serve to bring the fragments which must be masticated between the jaws, and further, they must be capable of being drawn upwards, as in the dog when he shows his teeth in preparing to bite.[18] Then come the movements of the jaws furnished with fangs for tearing, crushing, breaking, gnawing, and again the very complex movements of the tongue in drinking, licking, collecting the food in the mouth, forming it into a bolus, and finally despatching it.