Michael G. Collins blew my mind in the Green Bag. The symbol between the M and C in M‘Culloch is not an apostrophe (as I had thought), but an inverted comma, used to represent a superscript letter “c”:
Rather, as noted below, the upside down and backwards apostrophe turns out to have been a routine way for eighteenth and early nineteenth century printers to recreate a lower case, superscript “c” after the letter “M”. “Mc ” was itself an early abbreviation of the fully spelled out patronymic “Mac.”7 And the use of the lower-case superscript to indicate a contraction of letters ahead of the superscripted letter had been quite common in hand- written manuscripts.8
But two or three centuries ago, not all printers setting type by hand would have had a lower-case superscript “c” in their reper- toire. John Smith’s eighteenth century Printer’s Grammar indicates that most printers’ “founts” would not have included a “superior c”, and suggests that the “inverted comma” was a substitute for it.9 To make do, therefore, printers apparently took the piece of type for the comma, and turned it upside down when representing either “Mac” or “Mc ”.10 Thus the comma [,] when flipped, became [‘] – a poor man’s superscript “c”.
H/T Will Baude