a sheath; a theca; as, the vagina of the portal vein.-specifically, the canal which leads from the uterus to the external orifice if the genital canal, or to the cloaca.-the terminal part of the oviduct in insects and various other invertebrates. see illust., of spermatheca.-the basal expansion of certain leaves, which inwraps the stem; a sheath.-the shaft of a terminus, from which the bust of figure seems to issue or arise.