At Page 18 or thereabouts of my lecture on the Camel are accounts of the performances of the dromedary under the saddle. If not too late, let the above be fitly inserted by way of note, or introduced into the text, (of which, I have no copy) as shall seem to you convenient, observing what Horatius calleth the callida junctura. N.P. Perhaps it wasn't Horace, but what matters it?

References in this letter:

Marsh published two works on the Camel: "The Camel," in Report of the Smithsonain Institution for 1854, 98-122. 33 Cong. 2 Sess., Sen. Misc. Doc. 24. Washington, 1855. The Camel: His Organization, Habits and Uses, considered with Reference to His Introduction into the United States. Boston: Gould and Lincoln, 1856.

Latin:: expert or ingenious collocation (of words, phrases, and the like). From Horace's Ars poetica, line 47 - a famous phrase in hsitory of petic craftsmanship.