ORGANS OF DIGESTION. 125 
the walls of the abdominal cavity. It is a closed sac in the 
male, but in the female the Fallopian tubes open into it. 
The ligaments are the layers of the peritoneum suspend- 
ing other organs than parts of the alimentary canal. The 
suspensory or falciform ligament extends from the caudal 
surface of the diaphragm and the abdominal wall, to the sur- 
face of the liver, which its line of attachment divides into 
halves. The round ligament is the thickened free caudal 
border of the suspensory ligament. It is the remains of a 
vein which in fetal life joined the offspring to the mother. 
A third ligament connects the dorsal border of the liver with 
the diaphragm. The broad ligaments of the uterus are the 
folds of peritoneum which embrace the uterus, the Fallo- 
pian tubes, and the ovaries. The ovarian lgaments are 
short cords extending from the ends of the uterine cornua 
to the ovaries. The round ligaments of the uterus pass 
from the sides of the uterus to the brim of the pelvis. 
The peritoneum is called a serous membrane because of 
the colorless serum secreted by it. Other serous membranes 
are the pericardium of the heart, the pleura lining the tho- 
racic cavity and investing the lungs, and the synovial mem- 
branes of the joints. Serous membranes invest only such 
cavities as are not exposed to the air. All other cavities 
are lined by mucous membrane. A serous membrane con- 
sists of a layer of fibrous connective tissue covered by plate- 
like endothelial cells. 
REMARKS ON THE MAMMALIAN DIGESTIVE SYSTEM. 
The digestive system of mammals varies somewhat 
among the different groups. In carnivorous animals, as a 
rule, the alimentary canal is much shorter than in herbivo- 
rous. In the wildcat the canal is four times the length of 
the body, while the canal of the sheep is twenty times as 
