. Animal physiology. Physiology, Comparative; Physiology, Comparative. 454 ACTION OF MUSCLES OP ARM.—BONES OF SKULL. is bent upon the arm by a muscle, d, which arises from the top of the latter, and which is inserted at <?, at a short distance from the elbow-joint. Hence its contraction to a very slight extent will raise the hand through a considerable space ; but a propor- tional increase in its power will be required, to overcome any resisting force in the hand. The arm is straightened again, by an antagonist muscle, which lies on the back of the arm, and which is attached to a short proj
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 454 ACTION OF MUSCLES OP ARM.—BONES OF SKULL. is bent upon the arm by a muscle, d, which arises from the top of the latter, and which is inserted at <?, at a short distance from the elbow-joint. Hence its contraction to a very slight extent will raise the hand through a considerable space ; but a propor- tional increase in its power will be required, to overcome any resisting force in the hand. The arm is straightened again, by an antagonist muscle, which lies on the back of the arm, and which is attached to a short projection made by one of the bones of the fore-arm behind the elbow. This muscle also acts at a similar disadvantage in regard to power, and advantage in point of time ; in consequence of its point of attachment being so near to the fulcrum. Description of the Motor Apparatus of Man. 616. Before entering upon the examination of the various movements of the lower animals, and of the means by which these are effected, it will be useful to acquire a general knowledge of the structure of the Human Skeleton, and of the uses of its se- veral parts. The skeleton, which is formed by the union of 200 bones, is divided, like the body, into head, trunk, and members. The bones of these parts will now be separately described. 617. The Head is composed of two parts, the cranium or skull, and the face. The cranium is a bony case, of oval form, occupying the upper and back part of the head, and serving for the protection of the brain, which is lodged in its cavity. Its walls are made up of eight bones : the frontal, /, in the region of the forehead ; the two parietal bones, p, which occupy the top and sides of the skull; the two temporal bones, t, which form the walls of the temporal region ; the occipital bone, o, at the back of the head ; and the sphenoid, s, and the ethmoid, which assist in forming the floor of the cavity. These bones are firmly united. mi j Fig. 210.—Human Skull :/, fron-
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