The =cæcum= (Intestinum cæcum) is a great cul-de-sac intercalated
between the small intestine and the colon. It has a remarkable size,
shape, and position in the horse. Its length is three to four feet (ca.
1 to 1.25 m.), and its capacity about 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 abdominal 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 cæcus) 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
cæci) 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 cæci) 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 ventrally to the origin of the great colon. The body is
attached dorsally to the first part of the colon by the cæco-colic fold.
The apex is free, and consequently may vary in position.
[Illustration:
FIG. 266.—DIAGRAM OF CÆCUM AND LARGE COLON OF HORSE.
]
The cæcum has four =longitudinal bands= (Tæniæ), situated on the dorsal,
ventral, right, and left surfaces; these cause four rows of
=sacculations= (Haustra). The ventral band is entirely exposed or free
(Tænia libera); the dorsal band is free on the apex. The cæcal arteries
are placed on the other two. The right or parietal surface of the cæcum
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-cæcal orifice= (Ostium ileocæcale) 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 cæcum,
so that the orifice is surrounded by a fold of mucous membrane, forming
the =ileo-cæcal valve= (Valvula ileocæcalis). The peritoneum and
longitudinal muscle-fibers do not take part in its formation.
The =cæco-colic orifice= (Ostium cæcocolicum) is placed above and
external to the preceding one; the interval between them is only about
two inches (ca. 5 cm.), and they are separated by a distinct ridge which
projects into the interior of the cæcum. The orifice is slit-like and is
small in relation to the size of the cæcum and colon. It has a =valvular
fold= (Valvula cæcocolica) at its lower margin and a =muscular ring=
(Sphincter cæci). Large crescentic or semilunar folds (Plicæ cæci)
project into the cavity of the bowel, and between these are large
pouches (Cellulæ cæci).
[Illustration: