292 FASCIA 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."^ It begins at the ab- 

 dominal inguinal ring, and extends obhquely 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 ligament. The average length of the canal, measured 

 along the spermatic cord, is about four inches (ca. 10 cm.). 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 coxse. Its length is about six or seven 

 inches (ca. 15-17.5 cm.). 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 ring is determined by the 

 muscle becoming firmly attached to the ligament, i. 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 prepubic 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 cm.). The canal contains in the male the spermatic cord, the 

 tunica vaginalis, the external cremaster muscle, the external pudic artery (and in- 

 constantljr 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 cm.) apart. The distance measured along 

 the spermatic cord is about four inches (ca. 10 cm.). The medial angle of the subcutaneous ring 

 is well defined and distinctly palpable at the side of the prepubic tendon; from here the direction 

 of the ring is traceable. 



The Prepubic Tendon. — The prepubic tendon (Tendo prsepubicus) 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 pubic 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 

 Ugament, 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-Uke passage or space between 

 the two obhque muscles, since the inguinal hgament is that part of the aponeurosis of the exter- 

 nal oblique muscle which stretches between the tuber coxae and the prepubic tendon. 



' 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. 



