a, the attachment of the muscle to the shoulder-blade; P, attachment of the muscle to the fore-arm; F, elbow; W, hand. The movements of the limbs.—An excellent illustration of this relation between the bones and muscles is seen in the bending of the arm at the elbow. When the arm is bent, a great mass of flesh, the biceps muscle, in front of the upper arm may be observed to become much thicker. The muscle (Fig. 160) thickens because it becomes shorter. Its upper end is attached to the corner of the shoulder-blade (a), which remains stationary; while its lower end is connected at P with one of the bones of the fore-arm. The shortening of the muscle therefore draws [Pg 226] up the fore-arm. The elbow-joint, about which the motion takes place, is a very perfect hinge. Several other forms of joint are also found in various parts of the body. It is seen, when the skeleton is examined, that in every case the characters of the joints and the attachment of the muscles are most admirably adapted to the movements with which they are associated. The study of the skeleton.—The study of the rabbit’s skeleton is not only highly interesting in itself, but necessary for the intelligent appreciation of the animal’s life. And when it is compared with the skeletons of other familiar animals, a common plan of structure is found which illustrates in the most convincing manner the kinship which often exists between very dissimilar creatures. Such a comparison shows that, almost bone for bone, the skeleton of a rabbit corresponds with that of a man or a horse, and even with that of a bird or a frog. Mounted skeletons are shown in most natural-history museums, and the student should, whenever possible, examine and compare them.[9] He can himself, however, easily separate the bones from a boiled rabbit, and make out their main features and relationships. The rabbit’s skull and backbone—The bones of the head are collectively known as the skull. This consists of (1) a large brain case; (2) the cavities for the organs of special sense, viz., (a) a pair of nasal chambers (in which the organ of smell is located) in front: their hinder ends open into the top of the throat; (b) the eye-sockets at the sides, and (c) the flask-shaped chambers for the internal ears at the sides of the hinder end of the brain-case; (3) the jaws: the upper jaw is rigidly attached to the brain-case, but the lower jaw is hinged at each side on the hinder end of the bony arch which runs below the eye. Both upper and lower jaws bear teeth, which [Pg 227] are fixed in sockets. On each side the upper jaw contains two incisor teeth (p. 219) and—much further back—six grinding teeth. In the lower jaw are one incisor and five grinding teeth on each side. Fig. 161.—The Rabbit. The skeleton in position, seen from the left side.