Lewis Short
membrānŭla (noun F) : dim.id.
* A little skin or membrane.
* Lit.: membranula, quae sub cute calvariam cingit,Cels. 8, 4: oculi,membrane of the eye,id. 7, 7, 13.
* Transf.
* A parchment: iisque imperes, ut sumant membranulam,Cic. Att. 4, 4, b, 1.
* Plur., an instrument or document written on parchment: quae membranulis meā manu scriptis continebuntur,Dig. 32, 102 prooem.
Charlton T. Lewis, Charles Short, A Latin Dictionary