292 FASCL#£ AND MUSCLES OF THE HORSE 
the abdominal ring it descends the inguinal canal on the postero-lateral surface of 
the tunica vaginalis communis. 
Blood-supply.— External spermatic artery. 
Nerve-supply.— External spermatic nerve. 
The Inguinal Canal.—This term (Canalis inguinalis) is applied to an oblique 
passage through the posterior part of the abdominal wall.t It begins at the ab- 
dominal inguinal ring, and extends obliquely ventro-medially, and somewhat for- 
ward, to end at the subcutaneous inguinal ring. Its anterior wall is formed by the 
fleshy posterior part of the internal oblique muscle, and the posterior wall by the 
strong tendinous inguinal igament. The average length of the canal, measured 
along the spermatic cord, is about four inches (ca. 10 em.). The abdominal or 
internal inguinal ring (Annulus inguinalis abdominalis) is the internal opening of 
the canal; it is bounded in front by the thin margin of the internal oblique muscle, 
and behind by the inguinal ligament. It is directed from the edge of the prepubic 
tendon approximately toward the tuber cox. Its length is about six or seven 
inches (ca. 15-17.5 em.). The edge of the muscle is attached to the surface of the 
ligament here by delicate connective tissue, except where structures intervene be- 
tween the walls of the canal. The lateral limit of the rmg is determined by the 
muscle becoming firmly attached to the ligament, 7. e., actually arising from the 
latter. The subcutaneous or external inguinal ring (Annulus inguinalis subcutan- 
eus) is a well-defined slit in the aponeurosis of the external oblique muscle, lateral 
to the prepubie tendon. Its long axis is directed from the edge of the prepubic 
tendon outward, forward, and slightly ventrally, and its length is about four or five 
inches (ca. 10-12 em.). The canal contains in the male the spermatic cord, the 
tunica vaginalis, the external cremaster muscle, the external pudic artery (and in- 
constantly a small satellite vein), and the inguinal lymph vessels and nerves. In 
the female it contains the mammary vessels and nerves; in the bitch it also lodges 
the round ligament of the uterus, enclosed in a tubular process of peritoneum. 
The two rings do not correspond in direction, but diverge laterally, so that the length of the 
canal varies greatly when measured at different points. The medial angles of the two rings are 
separated only by a distance equal to the thickness of the prepubic tendon (about a centimeter), 
but the lateral angles are about seven inches (ca. 17.5 em.) apart. The distance measured along 
the spermatic cord is about four inches (ca. 10 em.). The medial angle of the subcutaneous ring 
is well defined and distinctly palpable at the side of the prepubie tendon; from here the direction 
of the ring is traceable. 
The Prepubic Tendon.—The prepubic tendon (Tendo preepubicus) is essentially 
the tendon of insertion of the two recti abdominis, but also furnishes attachment to 
the obliqui, the graciles, and the pectinei. It is attached to the anterior borders of 
the pubie bones, including the ilio-pectineal eminences. It has the form of a very 
strong thick band, with concave lateral borders which form the medial boundaries 
of the subcutaneous inguinal rings. Its direction is oblique upward and backward.? 
Its structure is somewhat complex. Most of the fibers of the posterior part extend 
from one ilio-pectineal eminence to the other. The fibers which belong to the recti 
curve in to the median line. The aponeuroses of the internal oblique muscles are 
inserted into its abdominal surface, and the inguinal ligaments are attached to and 
continue across it in arciform fashion. The anterior part of the tendon of origin 
of the gracilis is fused with it ventrally, and many of the fibers of the pectineus 
arise from it. It gives off on either side a strong round band, the so-called accessory 
ligament, which is inserted into the fovea of the head of the femur with the round 
The term canal is somewhat misleading; it is rather a slit-like passage or space between 
the two oblique muscles, since the inguinal ligament is that part of the aponeurosis of the exter- 
nal oblique muscle which stretches between the tuber cox and the prepubic tendon. 
2 The obliquity of the tendon and the angle which it forms with the pelvic floor are of clinical 
importance in regard to manipulation of the foetus in obstetrical cases. The slope varies in 
different subjects. In some cases the tendon forms about a right angle with the pubic bones. 
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