The =small colon= (Colon tenue) begins at the termination of the great
colon, behind the saccus cæcus of the stomach and below the left kidney,
and is continued by the rectum at the pelvic inlet. Its length is about
ten to twelve feet (ca. 3.5 m.), and its diameter about three to four
inches (ca. 7.5 to 10 cm.).
[Illustration:
FIG. 272.—PELVIC INLET AND POSTERIOR PART OF ABDOMINAL WALL OF HORSE,
VIEWED FROM THE FRONT.
The left inguinal canal is partially opened. The peritoneum is
retained except over a part of the left cremaster muscle. The
sublumbar region is greatly foreshortened in this view. _a_, _a′_,
Kidneys; _a″_, adrenal; _b._, ureter; _c_, renal artery; _d_, aorta;
_e_, cœliac artery (cut); _f_, anterior mesenteric artery (cut);
_g_, posterior mesenteric artery; _h_, circumflex iliac artery; _i_,
external iliac artery; _k_, internal iliac artery; _l_, spermatic
artery in peritoneal fold (plica vasculosa), _m_; _n_, vas deferens,
inclosed in urogenital fold, _o_; _p_, urinary bladder; _q_, round
ligament of bladder; _r_, middle ligament of bladder; _s_, rectum;
_t_, margin of vaginal ring; _u_, posterior abdominal artery; _v_,
external pudic artery; _w_, rectus abdominis muscle; _x_,
transversus and obliquus internus abdominis; _y_, _y′_, cremaster
externus; _z_, posterior vena cava (cut). (After Ellenberger-Baum,
Top. Anat. d. Pferdes.)
]
Its coils lie in the space between the stomach and the pelvic inlet,
dorsal to the left portions of the great colon. They are mingled with
those of the small intestine, from which they are easily distinguished
by the tæniæ and sacculation.
It is attached to the sublumbar region by the =colic mesentery=, and to
the termination of the duodenum by a short peritoneal fold (Lig.
duodeno-colicum). The great omentum is also attached to the origin of
the bowel. The colic mesentery is narrow at its origin, but soon reaches
a width of about three feet (ca. 80 to 90 cm.). Its parietal border is
attached along a line extending from the ventral surface of the left
kidney to the sacral promontory; it is continuous in front with the root
of the great mesentery, and behind with the mesorectum.
There are two =tæniæ= and two rows of sacculations. Of the tæniæ, one is
free, the other concealed by the mesentery. When the bowel is hardened
_in situ_ its lumen between the pouches is reduced to a narrow slit.