We have all remarked the rapid twitching of the skin by which dogs and horses rid themselves of flies. This movement is due to the rapid contraction of one of these muscles. It is easily proved that this is not in reality their office, for they are well developed in birds, fish, and reptiles that do not need to defend themselves from flies in this way. In all higher animals the traces of organs exist, which remind us of our kinship with the lower animals. Sometimes these organs retrograde from want of use, at other times they remain in existence but fulfil a very different office, and one always much less useful than the original one. Thus the cutaneous muscles still exist under the skin in many parts of the human body, as an inheritance and a sign transmitted to us by generations of animals that have preceded us on the earth. But the contractions of these muscles are no longer of any actual use. When the nerve-force in emotion spreads from the centre towards the periphery, these muscles, from their position in the skin, produce effects which are more easily seen than in other parts of the body, but which serve no effectual purpose in the struggle for existence and in the preservation of life. In the dog and cat, for instance, the contraction of these muscles in strong emotions causes the erection of the hair on the back, and gives the animal the characteristic expression of attack or defence, of fear or pain. In man, on the other hand, a forcible contraction of the cutaneous muscles of the neck which extend under the skin near the lips gives to the mouth the expression so characteristic of children when about to cry, or when they are trying to restrain their tears. Duchenne de Boulogne studied the function of this muscle, and showed that, when irritated by electric currents, it opens the mouth in the manner of one under the influence of terror. From Ehlers’ observations on the facial muscles of the gorilla and chimpanzee, we learn that these animals have the same muscles of the face as we have. Ehlers maintains that the statement made by certain authors is not true, namely, that the single fasciculi in the muscular system of the face of these animals are less thick and compact than in man. Only the wrinklings of the brow are less developed, and the muscles round the eye are finer, while those distributed to the nostrils and lips are more highly developed.