The histological changes occurring during the development of the bovine nuchal ligament have been observed in sections of formalin-fixed material from 21 animals ranging in age from 110 days of gestation to 10 yr. The elastic fibers which constitute the bulk of the adult ligament were initially few in number. During fetal development, the fibers showed a rapid increase both in number and in their stainability with the usual elastic stains. The average diameter of these elastic fibers increased only slowly until the last uterine month, at which time it began to increase very rapidly. This rapid rate of increase continued through the first 6 postnatal months, after which the rate of increase slowed markedly. However, the fiber diameter continued to rise steadily throughout the period of the study. During the fetal stage of development, the fibroblastic cells of the ligament exhibited unusual nuclear appearances which distinguish them from other fibroblasts. These consisted of marked clumping of the chromatin and an associated nuclear vacuolation or vesiculation. While these changes seem likely to be artefacts of fixation, their temporal correlation with elastin deposition and their demonstration in other tissue cells engaged in elastin production suggest that the factors responsible for these appearances may be related to elastin synthesis.

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