Lewis & Short

membrānŭla, ae, f. dim. [membrana], a little skin or membrane.

  1. I. Lit.: membranula, quae sub cute calvariam cingit, Cels. 8, 4: oculi, membrane of the eye, id. 7, 7, 13.
  2. II. Transf.
    1. A. A parchment: iisque imperes, ut sumant membranulam, Cic. Att. 4, 4, b, 1.
    2. B. Plur., an instrument or document written on parchment: quae membranulis meā manu scriptis continebuntur, Dig. 32, 102 prooem.