ESSENTIAL CONSTITUENTS OF HERNIA. 521 



on the abdomen, or development of gas in the bowel (tympanites), 

 all assist their formation, while rupture of the abdominal wall directly 

 produces them. Such rupture may be produced during parturition, 

 or by excessive exertion, severe pressure on the abdomen, or the 

 violent impact of blunt bodies. In men, external influences, such 

 as the pull of lipomatous new growths on the abdominal walls, may 

 induce local pocketing and prepare the way for ruptures ; but such 

 cases are seldom seen in animals. 



The essential constituents of a hernia are : — 



(1) The opening in the abdominal wall through which the viscus 

 has protruded may be a normal opening like the umbilicus, or one 

 abnormally dilated, as the inguinal canal sometimes is, or a rupture 

 in the abdominal coats, without solution of continuity in the skin. 



The rim of this orifice is termed the hernial ring. Its form and 

 size vary greatly. Sometimes it will only admit the little finger, 

 but in large animals it may be the diameter of a man's fist. Some- 

 times it is round, sometimes oval or slit-like. In umbilical and 

 inguinal hernia? it is lined with peritoneum. In a fresh ventral 

 hernia the edges of the ring are formed by the ruptured abdominal 

 coats. 



(2) The hernial swelling, which may vary from the size of a hazel 

 nut to that of a man's head or more, consists of the portion of pro- 

 truded viscus (" hernial contents "), and its coverings, the hernial 

 " sac." The latter is divided into neck and base. The hernial sac 

 consists of skin and subcutis, the latter usually thickened, sometimes 

 of layers of muscle and abdominal fascia?. The sacs of umbilical, 

 inguinal, and femoral hernia?, and those whose openings consist of 

 abnormally dilated physiological apertures, are lined with peritoneum. 

 In those produced by tearing of the abdominal walls, the peritoneum 

 is usually divided ; the internal organs may then lie under the subcutis, 

 and only be covered by the latter and the skin. 



The contents as a rule consist of either a loop of intestine (en- 

 terocele) or of omentum (epiplocele). Sometimes enterocele and 

 epiplocele co-exist forming entero-epiplocele. Only occasionally are 

 other internal organs like the stomach (gastrocele), uterus, bladder, 

 or liver found in the hernial sac. Sometimes the sac also contains 

 a serous fluid (hernial fluid). 



In reducible ruptures the contents lie free in the sac, and may 

 be returned to the peritoneal cavity (reposition, taxis) ; but some- 

 times the hernial contents and sac become adherent to one another, 

 and complete reposition can only be effected after division of the 

 adhesion. This constitutes irreducible hernia. The irreducible 



