Of Cainan - This Cainan, the son of Arphaxad, and father of Sala, is not found in any other Scripture genealogy. See Genesis 10:24; Genesis 11:12; 1 Chronicles 1:18, 1 Chronicles 1:24, where Arphaxad is made the father of Sala, and no mention at all made of Cainan. Some suppose that Cainan was a surname of Sala, and that the names should be read together thus, The son of Heber, the son of Salacainan, the son of Arphaxad, etc. If this does not untie the knot, it certainly cuts it; and the reader may pass on without any great scruple or embarrassment. There are many sensible observations on this genealogy in the notes at the end of Bishop Newcome's Harmony.
See, on this genealogy, the notes at Matthew 1:1-16.