The long-standing model of pigment cell origins is implicitly based upon a progressive fate restriction model of neural crest development and postulates the existence of a partially restricted progenitor common to all pigment cell types (i.e., a chromatoblast) [38] .
Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth's crust; it is the most abundant of the alkali group of metals. It is now obtained commercially by the electrolysis of absolutely dry fused sodium chloride.
A: Sodium is a metallic element on the periodic table with an atomic number of 11 and an atomic mass of 22.98 amu. This atomic mass is calculated by adding together the number of protons and neutrons present in the atom's nucleus. Sodium was discovered by Sir Humphrey Davy in 1807.