Somite

Thus A (from Latin somitus ) is the mesoblastic somite ( " somites " ) that occurs temporarily in the embryonic development of vertebrates and is formed from the Somitomer ..

The somites are pinched off in head -to-tail direction ( craniocaudal ) from the mesoderm lateral to the midline ( paraxial ). They therefore exist in two strands to the right and left of the axial structures notochord and neural tube.

Thus, the first consists of epithelium with a mesenchymal cavity, the Somitozöl. Later, the ventromedial is called ( directed toward the center of the abdomen) and as a proportion of mesenchymal sclerotome. The dorso-lateral ( to the side looking back ), epithelial remaining portion is called Dermatomyotom.

Derivatives of the somites

The Dermatomyotomen differentiate each in a dermatome, emerge from the dermis ( corium ) and subcutaneous ( under the skin ) and in a myotome (from the Greek mys " muscle "), which is the starting point for the trunk and limb muscles.

From the sclerotomes go forth, inter alia, the vertebrae. Here, a re-segmentation takes place by each of the rear portion of a sclerotome with the front of the next forms a vortex. The vertebrae are thus shifted by half a segment opposite the somites ( " somites "). The segmental back muscles that arise from the dermomyotome and are not resegmented, put on by to adjacent vertebrae.

Arthropods

Above all, in the arthropods under " somites " primary uniform body segments understood that normally sclerotized ( with calcium carbonate ( lime) impregnated ), said sclerites ( cover plates made ​​of chitin ) arise.