As a sequel to the study of the muscles of the region of the trunk very naturally comes the description of those which, belonging to the region of the coccyx, are destined for the movements of the caudal appendix, of which this latter constitutes the skeleton. The muscles may not seem to be of much importance with regard to external form, but, as they form part of the superficial muscular layer, and as the mass of each is seen in the form of the tail in some animals (the lion, for example), they merit our attention for a moment. A few lines will suffice to give an idea of them. They are: the _ischio-coccygeal_, _superior sacro-coccygeal_, _lateral sacro-coccygeal_, and _inferior sacro-coccygeal_. =The Ischio-coccygeal= (Fig. 18, 38; Fig. 69, 33; Fig. 70, 42).--This muscle, triangular in shape, better developed in the carnivora than in the horse, arises from the spine of the ischium, or from the supracotyloid crest, which replaces this latter in the solipeds and the ruminants. Thence its fleshy mass is directed upwards, expanding as it proceeds to be inserted into the transverse processes of the first two coccygeal vertebræ after insinuating itself between two of the following muscles, the lateral and inferior sacro-coccygeal. In the dog and cat, the muscle is in great part covered by the great gluteal. In the ox, by a peculiar arrangement of the corresponding region of the muscles of the thigh--an arrangement which we will examine in connection with the study of the latter--it is more exposed than in the horse, and gives origin to an outline which corresponds to its general form in the region situated immediately below the root of the tail. It is a depressor of the whole caudal appendix. =The Superior Sacro-coccygeal= (Fig. 68, 39; Fig. 69, 34; Fig. 70, 43).--The fasciculi which form this muscle arise from the crest of the sacrum, and proceed thence to end successively on the coccygeal vertebræ. It is in contact in the middle line with the corresponding muscle of the opposite side. It raises the tail and inclines it laterally; if the muscle of one side contracts at the same time as that of the other the tail is elevated directly. =The Lateral Sacro-coccygeal= (Fig. 68, 40; Fig. 69, 35; Fig. 70, 44).--Situated on the lateral part of the caudal region, this muscle arises, in the dog, from the internal border of the iliac bone and the external border of the sacrum; in the horse, it arises from the crest of the sacrum. It is inserted into the coccygeal vertebræ. It produces lateral movement of the tail. =The Inferior Sacro-coccygeal= (Fig. 68, 41; Fig. 69, 36; Fig. 70, 43).--This muscle, which is fairly thick, arises from the inferior surface of the sacrum and the corresponding surface of the sacro-sciatic ligament; it is inserted into the coccygeal vertebræ. It depresses the caudal appendix. Muscles of the Neck