The third molar is often absent in the English-speaking and Scandinavian races. In 46 per cent. of 670 patients it was missing. Frequently its development is abortive. This tooth, in the struggle for existence, seems destined to disappear. It is more often absent from the upper than the lower jaw. When absent, or badly developed, the jaw is smaller and frequently teeth irregularities, nasal stenosis, hypertrophy of nasal bone and mucous membrane, adenoids and eye disorders coexist. Fig. 62 shows absence of the left third molar with irregularities of that side of the arch. In Fig. 63 both third molars are seen to be missing. Anteriorly, the lateral incisors are most often wanting; 14 per cent. of the laterals were wanting in 670 patients. In the progress of evolution man has lost one lateral upon each side of the mouth and the second lateral seems also destined to disappear. In Fig. 64 the left lateral incisor has disappeared; and in Fig. 65 both lateral incisors are absent. Not infrequently does it occur that centrals, cuspids, bicuspids, and even molars are absent, even their germs not being detectable. Fig. 66 shows three supernumeraries in the anterior part of the mouth and but two molars. The absence of the teeth indicates lack of development of germs, due either to heredity or defective maternal nutrition at the time of conception or during early pregnancy. [Illustration: FIG. 65.] [Illustration: FIG. 66.] [Illustration: FIG. 67.] Crescent-shaped, bitubercular, and tribucular as well as deformed teeth, tend to be cone-shaped. The malformation of these teeth results from precongenital trophic change in dentine development, dwarfing and notching the cutting and grinding edges of the second set of teeth, of which a familiar example is the so-called Hutchinson's teeth, usually referred to a syphilitic causation. Hutchinson's position has, however, been more strongly stated than his words justify, since he admits that in at least one-tenth of the cases this cause could be excluded. Syphilis only plays the part of a diathetic state profoundly affecting the maternal constitution at the time of dentine development; while these teeth may be due to secondary results of syphilis, they do not demonstrate syphilitic heredity.