Somite


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Related to Somite: neural crest

somite

[′sō‚mīt]
(zoology)

Somite

 

a paired metameric formation in the embryos of such invertebrates as annelids and insects and in the embryos of man and all other chordates. The middle germ layer, or mesoderm, is segmented into somites during embryonic development. The somites are arranged along the longitudinal axis of the body alongside the neural tube and the chorda. The entire mesoderm is segmented in invertebrates, whereas in man and other chordates only its dorsal section is segmented, with the remaining mesoderm forming lateral plates, or splanchnotomes. Segmentation begins from the anterior section of the body and gradually extends to the posterior section. In the process of development, each somite decomposes into a myotome, a sclerotome, and a dermatome, from which are formed, respectively, the truncal musculature, the axial skeleton (in fish, also the skeleton of the fins), and the connective-tissue portion of the skin and its derivatives.

T. A. DETLAF

References in periodicals archive ?
Genital somite and third urosomite fused, without trace of division, forming genital double-somite; genital field located on anterior half of somite, with medial copulatory pore.
In addition, acupuncture injury at the 4th-5th somite from the cloaca was performed for in vivo observation of the dynamic macrophage and neutrophil migration process (Figure 3A and 3B).
Sound production was associated with tail-lifting behavior, suggesting that stridulation occurs on thoracic and/or abdominal somites.
Noggin acts downstream of Wnt and Sonic Hedgehog to antagonize BMP4 in avian somite patterning.
Pleon (Figs 3A, B): Five somites, somite 2 with 1 pair of dorsolateral processes directed anteriorly.
So far, there is no confirmation on expression of secretory factors by somite, whether they are able to co-express several neurogenic factors like noggin, chordin, follistatin, cer-berus and FGF8 in vitro.
Like the mesonephros, the skeletal system is also derived from the mesoderm, at approximately the same stage of development and at the same somite levels which are involved for the embryonic development of urogenital tract, which explains the skeletal abnormalities.
Abdomen armado con una espina media sobre la cresta transversal anterior del segundo y tercer segmento abdominal; una pequena espina sobre el margen posterior del segundo somite abdominal; cuarto segmento abdominal con una pequena espina media sobre el margen anterior; quinto y sexto segmentos relativamente lisos.
Each vertebra is formed from the combination of the caudal half of one somite and the cranial half of its neighbour.
The prepupa is more elongate, and upon the last abdominal somite presents a round protuberance with 3 lobes (Fig.