282 HEENI.E. 



deprived of their natural protection, will be specially liable to 

 injury from accidental causes. When serious interference with the 

 circulation of the contents of the tumour is caused by constriction 

 at the neck, the hernia is said to be strangulated or acute. It is 

 called chronic, if it remains unrelieved for a long time without 

 giving rise to acute symptoms, or it may be intermittent. An 

 acute inguinal hernia is seldom, if ever, intermittent; for it is of 

 such a nature that it hardy admits of spontaneous relief. A 

 hernia may be irreducible on aocoimt of the bowel having become 

 firmly adherent to the outside covering of the sac, as might happen 

 in old standing cases, in which there was interference with the 

 circulation of the part, though short of actual strangulation. 



ANATOilY. — The interior of the hody of the horse forms a large cavity, 

 which is divided across by a muscular partition (the diaphragm, or midriff), 

 into two parts, the thorax and the abdomen. The former contains, among 

 other organs, the lungs and heart ; the latter, the intestines, stomach, liver, 

 spleen and bladder. The interior of the abdomen is lined by a membranous 

 bag (the peritoneum) which covers the organs contained in the abdomen, 

 and which forms folds that serve as ligaments (1) to connect the intestines 

 together, and (2) to suspend them from the roof of the abdomen. The con- 

 necting layers of peritoneum are called omentum ; the suspending ones, 

 mesentery. 



There are two openings (the inguinal canals), one on each side, from the 

 abdomen into the scrotum. They are situated in the groin, close to the 

 stifle, are about 5i inches long, and run downwards, backwards, and in- 

 wards. Their upper opening (superior inguinal ring), which is smaller than 

 their lower opening, is, on each side, a little m front of the lower and 

 front edge of the floor of the pelvis (the pubes), and can be readily felt 

 with the fingers, by reason of the prominence of its front edge, if the hand 

 be passed through the anus into the bowel. In a stallion, a pouch of 

 peritoneum on each side, lines the inguinal canal and the scrotum, and at 

 its lower end gives lodgment for the testicle, the cord, blood-vessels, and 

 nerves of which pass upwards through the inguinal canal into the abdomen. 

 This pouch or bag of peritoneum forms the tunica vaginalis (Fig. 112). 

 In health, the small- intestine lies loosely over the inguinal canals, but does 

 not enter them. Under circumstances which cause hernia, the bowel or the 

 omentum, or both, may be forced into, or may slip through one or both 

 inguinal canals, and to a greater or less extent, into the scrotum. 



The navel is the site of the opening into the abdomen, through which the 

 navel-string that connected the foetus to the mare, passed. Shortly after 

 birth, the navel-string becomes divided, either accidentally or intentionally, 

 and the opening, under healthy conditions, soon closes up. The attempt at 

 closure may, however, be incomplete or defective from injury, ill health, or 

 hereditary predisposition, and a hernia at the navel may ensue. 



Acute Inguinal Hernia. 



An inguinal hernia is the passage through one of the inguinal 

 canals of a loop of intestine (Fig. 112), or a portion of omentum, 

 or of both. It may only just show through the inguinal canal, 

 or may descend low down in the scrotum (when it is termed by 

 some " scrotal hernia ") ; although it seldom comes down as low 



