Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
A hernia is formed by the protrusion of . certain abdominal organs through an acquired or congenital opening in the abdominal wall. The hernia always has three constituents present which include the hernial ring; the hernial sac which is composed of the peritoneum; and hernial contents which may include a loop of intestine or a portion of the uterus, stomach or omentum. According to their location, hernias are classified as umbilical, inguinal, scrotal, ventral, peritoneal or diaphragmatic.
"Repair of Umbilical Hernias in Swine,"
Iowa State University Veterinarian: Vol. 23
, Article 7.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol23/iss3/7