D'après MOORE JN. Visualization of equine gastrointestinal anatomy. In: International Veterinary Information Service, [en-ligne], 2003, [http://www.ivis.org/proceedings/Geneva/2003/moore/chapter_frm.asp?LA=1]
question 1
The cecum is a large, blind-ended fermentation vat, which is situated primarily on the horse's right side, extending from the paralumbar fossa region to the xyphoid cartilage on ventral midline. The cecum is 1.5 - 2 m in length and holds approximately 30 liters of feed and fluid. Contraction of the cecal musculature results in a coordinated mixing of the ingesta with the microorganisms that digest cellulose.
After the digestive processes in the cecum have altered the consistency and makeup of the ingesta, it passes through the ceco-colic opening into the first portion of the large colon, the right ventral colon. The right ventral colon is situated on the ventral aspect of the abdomen from the flank region to the rib cage. This portion of the colon has a diameter of approximately 25 - 30 cm and is divided by haustra into sacculations, which help mix and retain plant fibers until they are more fully digested. As the result of aboral muscular contractions, the ingesta moves towards the horse's left side through the sternal flexure of the ventral colon, and then into the left ventral colon. Inside the left ventral colon, which also is large and sacculated, the ingesta passes caudally towards the horse's left flank area. Near the pelvic region, the diameter of the colon decreases markedly and the colon folds back on itself. This region, which is called the pelvic flexure, is the initial portion of the unsacculated left dorsal colon.
Presumably due to the abrupt decrease in diameter, the junction between the left ventral colon and pelvic flexure is the most common location for impactions.
The ingesta then moves towards the horse's right side through the diaphragmatic flexure and into the right dorsal colon; the diameters of these portions of the colon are large, with that of the right dorsal colon reaching 30 - 35 cm. There are no sacculations in these portions of the dorsal colon, and the right dorsal colon is closely attached to the right ventral colon by a short fibrous mesentery and to the dorsal body wall by a tough common mesenteric attachment with the base of the cecum. In contrast neither the left ventral nor the left dorsal colons are attached directly to the body wall, allowing these portions of the colon to become displaced or twisted.
Ingesta in the right dorsal colon then moves into the short transverse colon, which has a diameter of approximately 10 cm and is situated cranial to the cranial mesenteric artery. The transverse colon is fixed firmly to the dorsal-most aspect of the abdominal cavity by a strong short fibrous mesentery. Finally, the ingesta enters the sacculated descending colon, which is 4 - 5 m in length and has a diameter of approximately 10 cm.
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