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 iDeginning 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. The}' 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) The lesser omentum (Omentum 

 minus),' which passes from the lesser curvature of 

 the stomach to the liver; (2) the gastro-splenic 

 omentum (Ligamentum gastrolienale), 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 curva- 

 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 (Pigs. 377, 378). A mesentery (Alesen- 

 terium) is a fold which attaches the intestine to 

 the dorsal wall of the abdomen. There are two 

 mesenteries, namely: (1) The great mesentery, 

 which connects the greater part of the small in- 

 testine with the dorsal abdominal wall; (2) the 

 colic mesentery, which attaches the small colon 

 to the dorsal abdominal wall. Ligaments are folds 

 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. 



Fig. 350. — Diagrammatic Cross-section 



OF Abdomex. 



To show arrangement of peritoneum 



when reduced to its simplest form. The 



external black line indicates the body-wall. 



1, Organ (e. g., kidney) in contact with wall; 



2, organ (e. g., small intestine) at a dis- 

 tance from wall; 3, parietal peritoneum; 4, 

 4, visceral peritoneum; 5, mesentery; 6, 

 peritoneal cavity. 



THE PELVIC CAVITY 



The pelvis is the posterior part of the trunk. It incloses the pelvic cavity 

 (Cavum pelvis), which communicates in front with the abdominal cavity, the hne 

 of demarcation being the terminal line or pelvic brim. 



The dorsal wall or roof is formed by the sacrum and first three coccygeal 

 vertebrae. The lateral walls are formed by the parts of the ilia behind the ilio- 



' Also known as the gastro-hepatio omentum. 

 ^ Also known as the gastro-colio omentum. 



