A small gut, or something resembling it; hence, a case or involucre (of a vein).
The inmost coating or membrane of a part or organ, esp. of a vein or artery.
Anatomy. The middle layer of the wall of a blood vessel or lymphatic vessel.
Anatomy. = tunic, n. 4a in various modern Latin collocations, as tunica adventitia, an outer sheath, esp. of a blood vessel; tunica albuginea, a…