THE SMALL COLON—THE RECTUM ; 429 
the three are continued on the right dorsal part. The ventral parts have alternate 
constrictions and sacculations (Haustra coli). 
On the right ventral colon two bands are dorsal, and extend along the medial and lateral 
sides of the attachment to the right dorsal colon. The medial one is covered by the colic vessels, 
ete., and the lateral one is concealed entirely or almost entirely by the attachment to the right 
dorsal part. A lateral band comes from the lesser curvature of the cecum and becomes ventral 
at the sternal flexure; itis free. The ventral band is also free. On the left ventral colon also two 
bands are dorsal. Of these, the medial one is covered by the vessels and lymph glands and in the 
anterior part also by the adhesion to the left dorsal part. At the pelvic flexure it is continued 
along the concave face of the bowel to the left dorsal part; it is important clinically as being the 
only distinct band on the flexure and may be felt per rectum. The dorso-lateral band is largely 
free, but is covered in front by the attachment to the left dorsal part. It fades out at the pelvic 
flexure. The ventro-medial and ventro-lateral bands are free and fade out at the pelvic flexure. 
The left dorsal colon has at first only one band, which is the continuation of the one along the lesser 
curvature of the pelvic flexure; it extends along the ventral surface and is continued on the right 
dorsal colon. Beyond the middle of the left dorsal colon two dorsal bands begin, diverge very 
gradually, and are continued on the right dorsal colon; both are free and broaden at the diaphrag- 
matic flexure. On the right dorsal colon the ventral band is concealed by the attachment to the 
right ventral colon and by the vessels and lymph glands. The two dorsal bands are free except 
at the parietal attachment of the bowel; the lateral one is very wide and somewhat indistinct; 
the medial one is narrower and more distinct, and is continued along the mesenteric border of the 
small colon. 
THE SMALL COLON 
The small colon (Colon tenue) begins at the termination of the great colon, 
behind the saccus cxcus of the stomach and ventral to the left kidney, and is con- 
tinued by the rectum at the pelvic inlet.t Its length is about ten to twelve feet 
(ca. 3.5 m.), and its diameter three to four inches (ca. 7.5 to 10 em.). 
Its coils lie chiefly in the space between the stomach and the pelvic inlet, 
dorsal to the left parts of the great colon. They are mingled with those of the 
small intestine, from which they are easily distinguished by the bands and sac- 
culation. 
It is attached to the sublumbar region by the colic mesentery, and to the 
termination of the duodenum by the narrow duodeno-colic fold of peritoneum 
(Lig. duodeno-colicum). The greater omentum is also attached to the initial 
part 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 longitudinal bands and two rows of sacculations. One of the 
bands is free, the other is concealed by the mesentery. When the bowel is hardened 
in situ its lumen between the pouches is reduced to a narrow slit. 
THE RECTUM 
The rectum (Intestinum rectum) is the terminal part of the bowel; it extends 
from the pelvic inlet to the anus.2_ Its length is about one foot (ca. 30 cm.). Its 
direction may be straight or oblique. The first or peritoneal part of the rectum is 
like the small colon, and is attached by a continuation of the colic mesentery termed 
the mesorectum. The second or retroperitoneal part forms a flask-shaped dilata- 
tion termed the ampulla recti; it is attached to the surrounding structures by con- 
nective tissue and muscular bands. 
The first part of the rectum commonly lies along the left wall of the pelvic 
cavity, but may be about median or (more rarely) deflected to the right. It is 
related to coils of the small colon and (inconstantly) to the left parts or pelvic 
1 The position of the funnel-shaped termination of the great colon and the origin of the small 
colon is fixed, and this fact is of clinical importance in regard to impaction, which is not rare here. 
In horses of medium size this part of the bowel can be palpated per rectum when distended. 
* There is no natural line of demarcation between the small colon and rectum: the plane 
of the pelvic inlet is selected as the division for convenience of description. 
