Embryogenesis of the styloglossus muscle in the human embryo. Its relationship with neighboring structures

Abstract Histogenesis of the muscles of the human tongue has been studied from the 15th week in utero onward: however their intrinsic or extrinsic origin is uncertain. The intrinsic musculature has sometimes be questioned (Saban, 1971). The embryogenesis of the styloglossus muscle has been studied in ten 39 to 58 day old human embryos. Its differentiation beyond the first lingual swellings in contact with a branch of the hypoglossus nerve allows its development to be followed outside the territories of the branchial arches. This study showed its progressive development, from day 42 onward, along bundles of the ceratoglossus and basioglossus muscles. The styloglossus muscle penetrates slowly on day 45 in the transverse fibres located behind the tongue. These latter differentiate earlier, independently and at the same time as the geniohyoid and genioglossus muscles, near the neural extensions of the hypoglossus nerve: they are very rapidly intermixed with the fibres of the genioglossus muscle: the other muscular fibres and those of the styloglossus muscle penetrate only later and progressively. In the current state of knowledge of axial neural organization, it can be concluded that the lingual muscles differentiate from the same type of cells recognized and innervated by the neurons of the hypoglossus nerve. The epigenesis of the different muscles is related to the appearance of their various functions.