82 COMPARATIVE ZOOLOGY. 
intestines lie more or less loose in the abdomen; but in 
the Crocodile, and likewise Birds and Mammals, they are 
supported by a membrane called mesentery. 
In Birds, the length of the alimentary canal varies with 
Fra. 46.—Anatomy of the Carp: br, branchie, or gill-openings; c, heart; f, liver; vn. 
swimming bladder; ez, intestinal canal; 0, ovarium; wu, urethra. The side-view 
shows the disposition of the muscles in vertical flakes. 
