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.
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 takes place that deformities of the dental arch result, the jaws vary from two inches to one inch in width. As a rule, the teeth are the same size to-day that they were thousands of years ago. This is due to the fact that they are ante-natal and not influenced by post-natal systemic changes. The jaws do not contract as a result of mouth breathing.[218] If the jaw be arrested and be smaller in circumference than the teeth, a break takes place in the dental arch and deformity results. Two types of deformity occur, the V-shaped arch and the saddle arch. All other types of deformity, not due to local causes, are modifications of these two. These deformities always occur with the second teeth only. In these cases the facial profile assumes the perpendicular line or arrested face, as illustrated in the chapter on Degeneracy of the Face. They are never seen before the sixth year, when the second set begin to erupt and are complete with development of the second molars at 12. They may become exaggerated later in life from want of room, the eruption of the third molar and want of harmony in relation of the two jaws when closed.
| FIG. 87. | FIG. 88. | FIG. 89. |