In reply to:

I wonder, does your copy include his definition of "internecine"? I read somewhere that the modern usage of that word derives from Johnson mistaking the purpose of the prefix inter- in connection with "necine."

max, you've outdone yourself! a self-YART no less!!

just so's you can rest easy on this one, here is the apposite OED entry, as near as I can purloin it:

App. first used as a rendering of L. internecinum bellum, in Butler's Hudibras (to which also is due the unetymological pronunciation). On this authority entered by Johnson in his Dictionary, with an incorrect explanation, due to association with words like interchange, intercommunion, etc. in which inter- has the force of ‘mutual’, ‘each other’. From J. the word has come into later dictionaries and 19th c. use, generally in the Johnsonian sense.]

1. orig. Deadly, destructive, characterized by great slaughter. internecine war, war for the sake of slaughter, war of extermination, war to the death.

2. esp. (In modern use.) Mutually destructive, aiming at the slaughter or destruction of each other.