Caecum (Lat. ccecus, blind), the rounded or sac-like commencement of the large intestine. The small intestine opens into the large intestine nearly at right angles, and at a distance of 2 1/2 inches from the commencement of the latter. This portion of the large intestine, included between its commencement and the opening of the small intestine, is called the caecum, or, in popular language, the blind gut, from its closed and rounded extremity. It is also called the caput coli, or head of the colon. It is the most capacious portion of the large intestine, its width being about equal to its length. It is situated in the right iliac region (see Abdomen), where it is retained in position by a fold of peritoneum and an attachment of loose cellular tissue. From its rounded extremity it sends off a narrow tubular prolongation, four or five inches in length, called the vermiform appendix, which is curled spirally in several turns, and is also retained in position by a peritoneal attachment. The specific functions performed by the caecum, as distinguished from the remainder of the large intestine, are not clearly understood.

It is sometimes the abode of a minute parasite, the trichocephalus dispar, which is rarely found in any other location.