Lewis & Short

2. insĕco or insĕquo, insexi, old form for insĕquor, to pursue the narration, to proceed, relate, declare; so imper.: insece, Musa, Enn. ap. Gell. 18, 9, 3 (Ann. v. 332 Vahl.): virum mihi, Camena, insece versutum, Liv. Andr. ap. Gell. 18, 9, 5; perf. subj.: insexit, dixerit, Enn. ap. Paul. ex Fest. p. 111 Müll.; gerund.: insecenda, Cato ap. Gell. 1. 1.