It's a very slow day, and so I can roll out the first (or maybe second) item (of many) that I've culled from old volumes of Notes and Queries that are available online at Project Gutenberg. This one's from Number 186, May 21, 1853:

_Crassus' Saying._--I find in the Diary of the poet Moore (in Lord John Russell's edition), vol. ii. p. 148., a conversation recorded with Dr.
Parr, in which the Doctor quotes "the witticism that made Crassus laugh (the only time in his life): 'Similes habent labra lactucas.'"

It appears (see the quotations in Facciolati) that this sage and laughter-moving remark of Crassus was made on seeing an ass eating a thistle; whereon he exclaimed, "Similes habent labra lactucas."

In Bailey's edition of Facciolati it is said, "Proverbium habet locum ubi similia similibus contingunt,... quo sensu Angli dicimus, 'Like lips like lettuce: like priest like people.'"

Out of this explanation it is difficult to elicit any sense, much less any "witticism."

I suggest that Crassus' saying meant, "His (the ass's) lips hold thistles and lettuces to be both alike;" wanting the discrimination to distinguish
between them. Or, if I may put it into a doggerel rhyme:

"About a donkeys taste why need we fret us?
To lips like his a thistle is a lettuce."


University Club.

Anyone know whether this noster Crassus (i.e. Dives)?