Degenerate teeth unite in twos, threes, fours, and fives. These single, cone-shaped teeth grow together and form bicuspids and molars. The germ of any two normal teeth may intermingle and unite; not only are the crowns found united with separate roots, but crowns and roots are united throughout. Figs. 80 and 81 show two superior, central and lateral incisors joined together throughout the entire length of crown and root. In Fig. 82 two lower incisors are united throughout. Fig. 83 shows a cuspid with two roots. George T. Carpenter, of Chicago, has a right superior, second bicuspid with three well formed roots. Fig. 84 illustrates two bicuspids united at the crowns. Fig. 85 shows two molars perfectly united. Fig. 86 illustrates central and lateral incisors of the permanent set perfectly united. Fig. 87 shows two molars united. Fig. 88 a molar and supernumerary taking the cone-shape with deformed centre. Fig. 89 shows three malformed teeth, each coated and completely united. It is not uncommon to find three molars united together, as, for instance, the second, third, and supernumerary molars. C. V. Rosser, of Atlanta, Georgia, has two small molars and a supernumerary cuspid perfectly united, from crown to root, and these three further united to the roots of a well-formed molar. [Illustration: FIG. 80.] [Illustration: FIG. 81.] [Illustration: FIG. 82.] [Illustration: FIG. 83.] [Illustration: FIG. 84.] [Illustration: FIG. 85.] [Illustration: FIG. 86.] That human jaws, like human ears, are degenerating is demonstrable by actual measurements. Mummery, who examined the skulls of 200 Briton and Roman soldiers, found the narrowest 2·12 inches, the highest 2·62, with an average of 2·50. The width of jaws of 402 British soldiers to-day is: narrowest, 1·88; widest, 2·63; average 2·28. The highest width was very rare; only eight measured 2·50. The jaws of the mound builders, compared with the existing cliff dwellers, show similar results. The average width is about 2·50 inches. This is also true of nearly pure negro races. Measurements of normal jaws of 855 Italians of Central Italy were: narrowest, 1·88; widest, 2·63; average 2·17. Measurements of normal jaws of 4,935 Americans gave the following results: narrowest, 1·75; widest, only one case, 2·56; average 2·13. If in the highest type of physical man the width of the upper jaw from the outer surface of the permanent molars near the gum margin was originally 2·50 inches in diameter, the jaw of people now living in the same locality is from 0·25 to 0·33 inches smaller. Although the jaw has thus been growing smaller, since there are no breaks or deformities in the contour of the dental arch this must be regarded simply as an adaptation to environment, and not degeneracy in the proper sense of the term. The degeneracy of the jaws, on which I would lay special stress, is that in which deformity has resulted from inability to adjust structure to a changing environment. When arrest of development so