[Fetal development and postnatal maturation of the longus colli muscle].

In adults, the predominant expression of a slow phenotype in the m. longus colli corresponds to its important postural function. Morphologically, there is a dispersion in fiber size predominating on the fast type 2 fibers which are significantly smaller than the slow type 1 fibers. We deemed it of interest, therefore, to analyze the metabolic differentiation of the muscle longus colli during its development. This study has been carried out on six anatomical samples, in foetuses aged between 16 and 40 weeks of pregnancy and in an 18 month-old child. The histological study combined H&E staining and immunohistochemical techniques (using antibodies specific for the slow and the fast isoforms of the myosin heavy chains). Our results indicate that the m. longus colli differentiates during the foetal period in a way which is quite comparable to that of other skeletal muscles, such as the quadriceps. In this series, a major slow predominance with a significant dispersion in fiber size was first observed in the 18 month-old child. Thus, it can be concluded that the establishment of the adult phenotype of this muscle starts during postnatal life, following the development of the mechanisms holding up the head and neck and leading to the appearance of the cervical lordosis.