 Its walls are comparatively thick; internally they are lightly longitudinally plicated, and have a whitish epitheloid lining.The penis opens into the posterior portion of the papillar structure in the form of a small tube; it proceeds through the thick vaginal wall in an oblique anterior direction, and becomes slightly enlarged or bulbous towards its termination.The vas deferens, as previously stated, is free to a very limited extent, and is imbedded in the vaginal wall.