364 



DIGESTIVE SYSTEM OF THE HORSE 



seven to eight gallons (ca. 25 to 30 liters). It is conical in form, and is curved 

 somewhat like a reversed comma. It is situated almost entirely to the right of 

 the median plane, extending from the right iliac and sublumbar regions to the ab- 

 dominal floor behind the xiphoid cartilage. Both extremities are blind, and the 

 two orifices are placed close together on the concave curvature. It presents for 

 description a base, a body, and an apex. 



The base (Saccus csecus) extends from about the thirteenth intercostal space 

 backward almost to the pelvic inlet. Its greater curvature is dorsal, its lesser 

 ventral; connected with the latter are the termination of the ileum and the origin 

 of the colon. The body (Corpus ciEci) extends downward and forward from the 

 base and rests largely on the ventral wall of the abdomen. Its lesser curvature is 

 about parallel with the costal arch and about five to six inches (10 to 15 cm.) below 

 it. The apex (Apex caeci) lies usually on the abdominal floor about a hand's 

 length behind the xiphoid cartilage. 



The base is attached dorsally by connective tissue and peritoneum on the 

 ventral surface of the pancreas and right kidney, the psoas muscles, and the iliac 

 fascia; internally, it is attached to the terminal part of the great colon, and ven- 



Origin of small colon 



Pelvic 

 flexure 



Diaphragmatic 

 flexure 



Stcryial 

 flexure 



Tleurrf 

 Fic. 266. — Diagram of C^cum and Large Colon of Horse. 



trally to the origin of the great colon. The body is attached dorsally to the first 

 part of the colon by the cseco-colic fold. The apex is free, and consequently may 

 vary in position. 



The caecum has four longitudinal bands (Tsenise), situated on the dorsal, 

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

 The ventral band is entirely exposed or free (Taenia libera); the dorsal band is 

 free on the apex. The ctecal arteries are placed on the other two. The right or 

 parietal surface of the caecum is related chiefly to the right abdominal wall, the 

 diaphragm, duodenum, and liver. The left or visceral surface lies against the left 

 divisions of the colon, the root of the great mesentery, and the small intestine. 



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

 of the base, about four or five inches (ca. 10 to 12 cm.) to the right of the median 

 plane and about opposite the lower end of the last rib. The end of the ileum is 

 partially telescoped into the caecum, so that the orifice is surrounded b}^ a fold of 

 mucous membrane, forming the ileo-caecal valve (Valvula ileocaecalis) . The 

 peritoneum and longitudinal muscle-fibers do not take part in its formation. 



The caeco-colic orifice (Ostium caecocolicum) is placed above and external to 



