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.
As we begin our exploration of the third period (row) of the periodic table, we find the element sodium (Na). Being in the first column, sodium is a member of the alkali metal family with potassium (K) and lithium (Li). Sodium's big claim to fame is that it's one of two elements in your table salt. When bonded to chlorine (Cl), the two elements make sodium chloride (NaCl). Sodium is also used as a salt in many fertilizers.