Large Intestines of the Horse
2. Colon:
A. Ascending Colon:
The ascending (great) colon begins at the cecocolic orifice and terminates in the transverse colon. It is a long U-shaped loop consisting of two parallel limbs and a terminal flexure. The U-shaped loop is folded on itself forming a double horseshoe-shaped loop. In situ, the two horseshoe-shaped loops lie more or less on top of each other. The ventral loop is called the ventral colon, and the dorsal loop is called the dorsal colon. This arrangement forms the following parts of the ascending colon: beginning at the right ventral colon; sternal flexure; left ventral colon; pelvic flexure; left dorsal colon; diaphragmatic flexure; and right dorsal colon that joins the transverse colon.
The right ventral colon (RVC) begins at the lesser curvature of the base of the cecum opposite the last rib. Initially it forms a curve with its convexity facing dorsocaudally. Then RVC passes cranioventrally along the right costal arch and then along the floor of the abdomen. It turns to the left over the xiphoid region forming the sternal flexure and continues as the left ventral colon. The RVC is attached to the cecum by the cecocolic fold.
The left ventral colon (LVC) passes caudally and dorsally on the abdominal floor. At the pelvic inlet it sharply bends dorsally and cranially forming the pelvic flexure, which is continued by the left dorsal colon.
The left dorsal colon (LDC) passes cranially along the left abdominal wall, dorsal and slightly lateral to the left ventral colon. Upon reaching the diaphragm and the left lobe of the liver, it turns to the right forming the diaphragmatic flexure, which lies craniodorsal to the sternal flexure.
The right dorsal colon (RDC) follows the diaphragmatic flexure, and passes caudally dorsal to the right ventral colon. On reaching the medial surface of the base of the cecum it turns to the left and dorsally to join the transverse colon. The RDC has the greatest diameter of any part of the colon.