_a_, Mucous membrane of cæcum; _b_, ileum; _c_. ileo-cæcal orifice;
_d_, fold of mucous membrane. (After P. Schumann.)
]
The =great colon= (Colon crassum) begins at the cæco-colic orifice, and
terminates by joining the small colon behind the saccus cæcus of the
stomach. It is ten to twelve feet (ca. 3 to 3.7 m.) long, and its
average diameter (exclusive of its narrowest part) is about eight to ten
inches (ca. 20 to 25 cm.). Its capacity is more than double that of the
cæcum. When removed from the abdomen, it consists of two parallel
portions, which are connected by peritoneum and partially by areolar
tissue also. _In situ_, it is folded so that it consists of four parts,
which are designated according to their position or numerically. The
three bent connecting parts are termed the flexures. The first, =right
ventral part= (Colon ventrale dextrum), begins at the cæco-colic orifice
about opposite the middle of the last rib, passes downward and forward
along the right costal arch, and reaches the floor of the abdomen. Over
the xiphoid cartilage it bends sharply to the left and backward, forming
the =sternal flexure= (Flexura diaphragmatica ventralis). The second,
=left ventral part= (Colon ventrale sinistrum), passes backward on the
left part of the abdominal floor, and, on reaching the pelvic inlet,
bends sharply dorsally and forward, forming the =pelvic flexure=
(Flexura pelvina). This is continued by the third, =left dorsal part=
(Colon dorsale sinistrum), which passes forward above the left ventral
portion. On reaching the stomach, diaphragm, and left lobe of the liver,
it turns to the right, forming the =diaphragmatic= or =gastro-hepatic
flexure= (Flexura diaphragmatica dorsalis). The fourth or =right dorsal
part= (Colon dorsale dextrum) passes backward above the first portion,
and on reaching the inner or left surface of the base of the cæcum it
turns upward and to the left behind the left sac of the stomach; here it
becomes constricted, and joins the small colon below the left kidney.
[Illustration: