#Paraxial mesoderm forms during [[Developmental Biology - Gastrulation - Anatomy & Physiology|gastrulation]].
#It forms a mesenchymal ''pre - somitic mesoderm'' tissue starting at the anterior and moving posteriorly.
#It forms a mesenchymal ''pre - somitic mesoderm'' tissue starting at the anterior and moving posteriorly.
#At the anterior, the pre - somitic mesoderm becomes organsised into blocks of cells called '''somitomeres'''.
#At the anterior, the pre - somitic mesoderm becomes organsised into blocks of cells called '''somitomeres'''.
#*Somitomeres are compacted and cells undergo a mesenchymal to epithelial transition.
#*Somitomeres are compacted and cells undergo a mesenchymal to epithelial transition.
−
#*They then separate from the rest of the pre - somitic mesoderm to from somites.
+
#*Somitomeres then separate from the rest of the pre - somitic mesoderm to from somites.
−
#As somites "bud off" at the anterior, more pre - somitic mesoderm develops posteriorly. This means that the total length of the pre - somitic mesoderm remains constant.
+
#As somites "bud off" at the anterior, more pre - somitic mesoderm develops posteriorly. Thus, the total length of the pre - somitic mesoderm remains constant.
*Pre - somitic mesoderm forms somites at regular intervals; one forms every 90 minutes.
*Pre - somitic mesoderm forms somites at regular intervals; one forms every 90 minutes.