an early form of the possessive was : " the man his arm...."

I have read some notes scattered about that point towards the "man his arm" theory behind the adoption of the apostrophe, but the more accepted (correct me, others) theory is that the genetive singular form most often used ended in -es (reached back into the days when the language had cases). In the Middle English inflectional system, the accusative and dative cases were replaced with prepositions, but the genetive did the trick using an apostrophe. The unstressed e dropped out of pronunciation, and writers placed an apostrophe to indicate the dropped letter (some sources debate whether the apostrophe denotes an omission).

Brandon