Matthew Poole and continuators on Genesis 50:3

3 And forty dayes were fulfilled for him , (for so are fulfilled the days of those which are embalmed) and the Egyptians mourned for him threescore and ten dayes .

(i. e.) For his embalming; that so the Drugs or Spices which were applied might more effectually reach to all the parts of the dead body, and keep it from corruption. And the effect of their diligence and so long continuance in this work was that bodies have been preserved uncorrupt for some thousands of years.

(i. e.) Thirty days, according to the custom of the Hebrews, Numb. 20. 29. Deut. 34. 8. to which doubtless the Egyptians in this case did accommodate themselves, besides the forty days spent in embalming him, which also was a time of mourning. And thus I suppose, the Egyptians reckoned those seventy two dayes which Diodorus Siculus saith they spent in mourning for their deceased Kings.

Marginal references: Heb. wept.