424 



DIGESTIVE SYSTEM OF THE HORSE 



to the first part of the colon In- the cseco-colic fold. The apex is free, and conse- 

 quently may vary in position. 



The cagcum has four longitudinal bands (Taeniae cseci), situated on the dorsal, 

 ventral, right, and left surfaces; these cause four rows of sacculations (Haustra). 



The ventral band is almost entirely exposed or free (Taenia libera) ; it begins on the highest 

 part of the base, extends along the medial side of the greater curvature, and joins the medial band 

 near the apex. It is concealed only at its origin where the bowel is attached to the wall. The 

 dorsal band extends along the lesser curvature from the termination of the ileum to the apex. 

 The medial band extends along the medial part of the lesser curvature of the base, inclines 

 ventrally further forward, and ends by joining the ventral band. It is covered at its origin by the 

 adhesion to the right dorsal part of the great colon and beyond this by the cascal vessels and lymph 

 glands. Medial to the termination of the ileum it projects from the wall of the bowel as a falciform 

 band which can be felt distinctly although covered by vessels and fat. The lateral band is 

 continuous with that of the right ventral part of the colon. It is covered by vessels, lymph glands 

 and fat, but can be felt in its posterior part, where it forms a concave projecting edge. It inclines 

 ventrally in front and may extend to the apex or fade out without reacliing it. 



Fig j()j — Orifices of C.ecum of Horse. 

 1, Ileo-CEBcal orifice; 2, CEeco-colic orifice; 3, intervening fold. 



The ileo-caecal orifice (Ostium ileocaecale) is situated in the lesser curvature of 

 the base, about two or three inches (ca. 5 to 7.5 cm.) to the right of the median 

 plane, and in a transverse plane through the first or second lumbar vertebra. The 

 end of the ileum is partially telescoped into the caecum, so that, the orifice is sur- 

 rounded by a fold of mucous membrane which encloses a thick circular muscular 

 layer, the sphincter ilei. 



The caeco-colic orifice (Ostium caecocolicum) is lateral to the preceding one; 

 the interval between them is only about two inches (ca. 5 cm.), and they are separ- 

 ated by a large fold which projects into the interior of the caecum. The orifice is 

 small in relation to the size of the caecum and colon. It is slit-like, or has a narrow 

 oval outline, and is about two inches (ca. 5 cm.) long. It has a thick valvular fold 

 (Valvula cascocohca) at its ventral margin and is encircled by a muscular ring, the 

 sphincter cffici.^ Large crescentic or semilunar folds (Plicae caeci) project into the 

 cavity of the bowel, and between these are large pouches (Cellulae caeci) . 



/ The anatomical arrangement gives no support to the view which is sometimes expressed 

 that ingesta may pass directly from the ileum to the colon. 



