The following are the summary of our study on finger nails of 195 youth (112 male and 83 female students). The classification of the nail type is based on that of MARTIN-SALLrx, in which nails are classified into 11 types. In the present study each of the 11 types is further subdivided into 2 sub-types, hence 22 types in all.
1. Concerning the frequency of each finger nail type, Type II and Type II' appear with over 40% incidence on both sides of the first finger, but other types are of only less than 5% incidence. In the second finger, too, the Type II appears with over 40% incidence and type II-a in 20%. In the third finger, Type II and Type II-a' appear with about 20% incidence, but Type II is of 15% incidence which is less than half of that in the first or the second finger. In the fourth finger, Type II', Type II-a' and Type IV' appear with approximately 20% incidence, but Type II is reduced to 9 to 10%. In the fifth finger, Type II' appears in 3%, and Type I, Type II, Type II-a and Type II-a' appear in 10 to 15% respectively.
As for the frequency of each nail types in females, Type II appears in 40 to 50%, Type II' in about 30% and Type I in 10% in the first finger. In the second finger, both type II and Type II-a appear in about 20% and Type I and Type II-a in about 10%. In the third finger, both Type II-a and the Type II-a' appear in 20%, and Type II in 15% and Type II' in 10%. In the fourth finger, Type II-a' appears in more than 30%, the type II' in 15%, Type I-a and Type Vin approximately 10%. In the fifth finger, Type II-a appears in 20% to 26%, Type I-a', Type II' and Type II-a in approximately 10% to 15%.
2. There is no difference among each nail type of each finger on both sides in both males and females.
3. There is no sexual difference among each nail type in the first finger. The nail types which appear significantly larger in males are Type II in the second finger, Type II' in the second, third and the fifth fingers and Type IV' in the third, fourth and the fifth fingers. In females, Type VII in the second finger, Type I-a in the second, third, fourth and the fifth fingers, Type II-a' in the fourth finger, Type I-a' in the fifth finger appear significantly more than in males.
4. The incidence of nail types with concave-shaped covered margin is as low as about 5% in the first finger on both sides in both sexes, but is 30 to 40% in the second, third, fourth and the fifth fingers on both sides in the male and is as high as 56 to 76% in females. The sexual difference in covered nail margin is not existing in the first finger, but concave-shaped types appear significantly more in the second, third, fourth and fifth fingers of females. On the contrary, the straight covered margin appear significantly more in the second, fourth and the fifth fingers on both sides in males.
5. The nail type in which free margin does not exceed the finger tip appears in 30% on both sides in the second finger, and in more than 50% in other four fingers in males. Among females, it appears in lower percentage of about 20% in the second finger, but in more than 50% in the first, third and fifth fingers, and in more than 70% in the fourth finger. Therefore, in both sexes, the type of the nail extending to the tip of the finger is more common in the second finger, whereas, in the fourth finger, the type of the nail which does not extend to the tip of the finger is more common.
