Tubular glands that lie between the finger-like projections (see villus) of the inner surface of the small intestine. The cells of these glands (called Paneth cells) secrete components of the succus entericus (intestinal juice) as they gradually migrate along the side of the crypt and the villus; they are eventually shed into the lumen of the intestine. The glands are named after German anatomist J. N. Lieberkühn (1711–56).