INGUINAL HERNIA IN THE HORSE. 
281 
pigs, less seldom in ruminants and dogs, and the sac usually contains 
intestine, less frequently omentum. As inguinal hernia exhibits certain 
peculiarities in the different classes of animals, it will he considered 
separately in each. 
(1.) INGUINAL HERNIA IN THE HORSE. 
In stallions and geldings the inguinal canal consists of a flat funnel-shaped 
passage about 4 inches in length, whose upper opening (annulus abdominis) is 
from | to 1 \ inches in length, but occasionally much wider. It extends in an 
oblique direction from behind outwards and forwards, is situated 1 to 2 inches 
from the oblique branch of the os pubis, and 4 to 6 inches from the linea alba. 
Anteriorly and inwardly the abdominal ring is bordered by the posterior edge 
of the inner oblique abdominal muscle, posteriorly and outwardly by the 
cremaster or spermatic cord. The vessels supplying the posterior portion of 
the abdominal walls pass about § of an inch from its posterior angle, and on 
its inner side. The inguinal ring or outer abdominal ring (annulus inguinalis) 
consists of a slit between the inner and outer tendinous heads of the external 
oblique abdominal muscle, whose posterior inner angle lies \\ inches in front 
of the branch of the os pubis, and somewhat further from the middle line of 
the abdomen. Its normal length is about 4 inches ; it likewise passes for¬ 
wards and outwards, and opens when the thigh is directed backwards and 
abducted. The anterior inner wall of the inguinal canal is largely formed by 
the inner oblique abdominal muscle, the outer by the crural arch or Poupart s 
ligament. 
Causes. In stallions with abnormally wide abdominal rings, and less 
frequently in geldings, the small intestine or omentum may enter the 
inguinal canal. According to Berdez, Vogel, Stockfleth, and otheis, the 
condition is always caused by excessive width of the ring; whilst 
Lafosse, H. Bouley, and Gerlach declare that inguinal hernia may occur 
even where the aperture is of normal width. But even if we allow this, 
there is no doubt that in by far the greater number of cases the condi¬ 
tion is due to abnormal width of the ring, which sometimes measuies 
4 to 6 inches. Holler has, however, also seen inguinal hernia in horses 
in which the inner ring scarcely allowed the entrance of two fingers, 
though, as a rule, two easily pass in addition to the spermatic cord. It 
is therefore difficult to fix a normal width and settle this question, which 
requires numerous measurements to be made in different laces of 
animals. Inguinal hernia is generally congenital, oi appears duiing the 
descent of the testicle. The tendency to it seems to be inlieiited. It 
has even been seen in the foetus. Its production is favouied by all 
circumstances which cause increased abdominal pressuie, such as 
tympanites, severe exertion, hard drawing on soft ground (where the 
action of the muscles in lifting the feet also produces dilatation of the 
abdominal ring), or struggling in hobbles. Hammerschmid’s case shows 
that difficult labours may produce inguinal herniae in the foal, particularly 
