Fig. 54. 1, The body of the lower jaw. 2, Ramus, or branch of the jaw, to which the muscles that move it are attached. 3, 3, The processes which unite the lower jaw with the head. i, The middle and lateral incisor tooth of one side. b, The bicuspid teeth. c, The cuspids, or eye teeth. m, The three molar teeth. A, shows the relation of the permanent to the temporary teeth.
215. The first set, which appears in infancy, is called tem´po-ra-ry, or milk teeth. They are twenty in number; ten in each jaw. Between six and fourteen years of age, the temporary teeth are removed, and the second set appears, called per´ma-nent teeth. They number thirty-two, sixteen in each jaw.
214. Where and how are the teeth formed? Explain fig. 54. 215. What are the first set called? How many in each jaw? The second set? How many in number?
216. The four front teeth in each jaw are called in-ci´sors, (cutting teeth;) the next tooth in each side, the cus´pid, (eye tooth;) the next two, bi-cus´pids, (small grinders;) the next two, mo´lars, (grinders.) The last one on each side of the jaw is called a wisdom tooth, because it does not appear until a person is about twenty years old. The incisors, cuspids, and bicuspids, have each but one root. The molars of the upper jaw have three roots, while those of the lower jaw have but two.
Fig. 55.
Fig. 55. The permanent teeth of the upper and lower jaw. a, b, The incisors. c, The cuspids. d, e, The bicuspids. f, g, The molars, (double teeth.) h, The wisdom teeth.
Observation. The shape of the teeth in different species of animals is adapted to the kind of food on which they subsist. Those animals that feed exclusively on flesh, as the lion, have the cuspids, or canine teeth, largely developed, and the molars have sharp cutting points. Those animals that feed on grass and grain, as the horse and the sheep, have their molar teeth more rounded and flat on the crown. The human teeth are 108 adapted to feed on fruits, grain, or flesh, as they are less pointed than those of the cat, and more pointed than those of the sheep.