412 DIGESTIVE SYSTEM OF THE HORSE 
othelial cells, and is moistened by the peritoneal fluid. Friction is thus reduced 
to a minimum during the movements of the viscera. The outer surface of the peri- 
toneum is related to the subserous tissue, which attaches it to the abdominal wall 
or the viscera. 
In order to understand the general disposition of the peritoneum, we may 
imagine the abdominal cavity to be empty and lined by a simple layer of perito- 
neum, termed the parietal layer (Lamina parietalis). We may further imagine 
the organs as beginning to develop in the subserous tissue, enlarging, and migrat- 
ing into the abdominal cavity to a varying extent. In doing so they carry the per- 
itoneum before them, producing introversion of the simple sac, and forming folds 
which connect them with the wall or with each other. The viscera thus receive 
a complete or partial covering of peritoneum, termed the visceral layer (Lamina 
visceralis). The connecting folds are termed omenta, mesenteries, ligaments, 
etc. They contain a varying quantity of connective tissue, fat, and lymph glands, — 
and furnish a path for the vessels and nerves of | 
the viscera. Some contain unstriped muscular 
tissue. An omentum is a fold which passes from 
the stomach to other viscera. There are three of 
these, namely: (1) Thelesser omentum (Omentum 
minus),' which passes from the lesser curvature of 
the stomach to the liver; (2) the gastro-splenic 
omentum (Ligamentum ae which ex- 
tends from the greater curvature of the stomach 
to the spleen; (3) the greater omentum (Omen- 
tum majus),” which passes from the greater eurya- 
ture of the stomach and from the spleen to the 
terminal part of the great colon and the origin of 
the small colon. It does not pass directly from 
one organ to the other, but forms an extensive 
loose sac (higs. 377, 378). A mesentery (Mesen- | 
Fic. 350.—Dracrammaric Cross-section terium) is a fold which attaches the intestine to 
OF ABDOMEN, the dorsal wall of the abdomen. There are two | 
when reduced to its simplest form, The ™esemteries in the horse: (1) The great mes 
external black line indicates the body-wall. entery connects the greater part of the small 
1, Organ (e. g., kidney) in contact with wall; intestine with the dorsal abdominal wall; () 
2, organ (e. g., eal intestine) at a dis- : 
tance from wall: 3, parietal peritoneum: 4, the colic mesentery attaches the small colon to 
4, visceral peritoneum; 5, mesentery; 6, the dorsal abdominal wall. Ligaments are folds 
peritones| cava: which pass between viscera other than parts of the | 
digestive tube, or connect them with the abdom- | 
inal wall. The term is also applied to folds which attach parts of the digestive tract 
to the abdominal wall, but do not contain their blood-vessels and nerves. Some (e. g., 
the lateral and coronary ligaments of the liver) are strengthened by fibrous tissue; 
others (e. g., the broad ligaments of the uterus) contain also unstriped muscular 
tissue. 
| 
To show arrangement of peritoneum 
THE PELVIC CAVITY 
The pelvis is the posterior part of the trunk. It incloses the pelvie cavity) | 
(Cavum pelvis), which communicates in front with the abdominal cavity, the line) | 
of demarcation being the terminal line or pelvic brim. 
The dorsal wall or roof is formed by the sacrum and first three coceymeall 
vertebra. The lateral walls are formed by the parts of the ilia behind the iho- 
1 Also known as the gastro-hepatic omentum. 
° Also known as the gastro-colic omentum. 
