Growth of second metacarpal of American-Japanese hybrids.

Viewed as a function of chronological age and skeletal maturity (K method), this paper examined growth of the second metacarpal in the hybrids between American men and Japanese women. Radiographs of their right hand and wrist were taken from 1958 to 1965 longitudinally. The semi-longitudinal samples comprised those of 458 American Black- and 653 American White-Japanese hybrids and 429 Japanese, 3-19 years old. According to age, the hybrids followed roughly a similar pattern of growth in the bone length to their paternal Americans. Their values were usually placed in an almost intermediate position between those of their parental groups. The bone showed few differences in width between the hybrids and their parental groups, but the relationship between them was complicated. In the width/length index, the hybrids followed roughly a similar course of age changes rather to the Japanese at the early ages, but after puberty, they were placed in an intermediate position between their parental groups. According to skeletal maturity, the bone length and width revealed a significant linear regression in each group. Significant differences were found for the regression of the length to skeletal maturity between the hybrids and Japanese. The bone length increased more rapidly in the hybrids than in the Japanese as it matures. Thus, the genetic control could become dominant gradually in the bone length at least from the start, as skeletal maturity progresses.