The part of the large intestine extending from the cecum to the rectum. It has the same basic design in all species. There is an ascending colon which begins at the cecum, passes forward to the cranial part of the abdominal cavity then crosses to the left side as the transverse colon. It then turns caudally again to become the descending colon. In the caudal abdomen the colon curves to the midline and joins the rectum. See also colonic.
In herbivores and omnivores there is a variation on this general plan in that the ascending colon is greatly lengthened. In the ruminants and the pig this takes the form of a spiral colon of centrifugal and centripetal loops which occupies the right side of the abdomen. In the horse the ascending colon forms an uncoiled loop reflexed upon itself, beginning at the cecum as the right ventral colon, passing to the left ventral, to the left dorsal at the pelvic flexure, then to the right dorsal, then back into the standard pattern at the transverse colon. In the horse there is the additional oddity of a significant reduction in diameter at the small colon, the terminal part which joins the rectum.
- ascending c. — the first segment of the colon which is either a short, cranially directed segment, as in the dog, or greatly expanded to form the spiral colon in ruminants, or the great colon of horses (right ventral, sternal flexure, left ventral, pelvic flexure, left dorsal, diaphragmatic flexure, right dorsal colons).
- coiled c. — see spiral colon (below).
- descending c. — the third and last of the three main divisions of the colon which runs caudally and terminates in the rectum. It is not extensive in the horse, in which it has an unusually long mesentery and is known as the small colon.
- floating c. — small or descending colon in horses.
- irritable c. syndrome — stress and psychological factors can cause the frequent passage of soft to watery feces, often with mucus, in dogs. Called also mucous colitis, spastic colon, psychologically induced colitis, and irritable bowel. See also spasmodic colic.
- large c. — the ascending colon of the horse.
- left c. displacement colic — forward displacement of the left dorsal colon is an uncommon cause of moderate colic in the horse. Characteristic findings include a palpable medial displacement of the spleen and the absence of the pelvic flexure of the colon from its usual site in front of the pelvis. Surgical removal of the displaced colon from its entrapment across the top of the gastrosplenic ligament is the only effective treatment.
- short c. — see descending colon (above).
- redundant c. — extra bends in the descending colon. Seen on x-rays, especially in large breed dogs.
- small c. — see descending colon (above).
- spiral c. — ascending colon of ruminants.
