The histological changes occurring during thc development of the bovinc nuchal ligament have been observed in sections of formalin-fixed material from 21 animals ranging in age from I l0 days of gestation to l0 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. Thc average diameter of these clastic fibcrs increased only slowly until the last uterine month, at which time it began to increase very rapidly. This rapid rate of increase continued through thc 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 vcsiculation. 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 appearanccs may be related to elastin synthesis.In the accompanying paper (1), the pattern of changes in chemical composition during the development of the bovine nuchal ligament has been reported. At the time of collection of the ligaments, samples were taken for histological examinations. The histological findings have not only contributed to the interpretation of the chemical data, but have also established the suitability of this tissue for studies of elastin fibrillogenesis. In addition, they have revealed several unusual features relating to the fibroblasts which constitute the mass of the cell content. For these reasons and as the nuchal ligament seems likely to become the subject of further detailed studies, the main features of the morphological changes during the development are also reported.
MATERIALS AND METHODSThe experimental animals and the methods of collection of the ligaments were described in the accompanying paper (1). For the histological study, examination was made of sections of material taken from ten fetal calves ranging in age from 110 days of gcstation of full term, and from 11 postnatal animals bctwecn 2 wk and 9 yr of age. In each instance, transverse sections and sections parallel to the long axis of the ligament were examine& The ligament specimens were fixed for 48-72 hr in 10% neutral formalin. After dehydration, the specimens were embedded in paraffin and sectioned at 7 ]z. Serial sections were stained by the following methods: hematoxylin and eosin,
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