290 THE ANATOMY OF THE HORSE. 



iis having two extremities, two sui-faces, and two edges. Its extremities 

 are attached to the pubis and angle of the haunch respectively. Its 

 anterior surface is concave, and directed towards the abdomen. This 

 surfiice gives origin outwardly to fibres of the internal oblique muscle, 

 and inwardly it foi-ms the posterior wall of the inguinal canal. The 

 posterior surface is convex, and forms an arch over the femoral vessels, 

 the crural nerve, and the sartorius, iliacus, and psoas magnus muscles 

 (Plate 13). Neither of the edges of the ligament has a distinct [exist- 

 ence. The posterior or inferior edge is the line of continuity between 

 the ligament and the tendon of the external oblique. At its anterior or 

 superior edge the ligament becomes thin in texture, and disappears on 

 the fascia covering the sublumbar muscles. All of these points cannot 

 be made out at present, but they will become evident as the dissection 

 proceeds. 



Action of the external oblique muscle. — When the right and left 

 muscles act in concert, they bend the tnink, and arch the back. If the 

 spine is fixed, they p\ill the ribs backwards and assist in expiration. If 

 both the spine and ribs are fixed, they compress the abdominal viscera, 

 and assist in urination, defeecation, and parturition. If only one muscle 

 acts, it bends the trunk or pelvis to the same side. 



The Inguinal Canal is the oblique passage in the abdominal w^all 

 through which the testicle descends in the young animal, and in which 

 the spermatic cord is lodged in the adult. The extetiuxl abdominal ring, 

 which has already been examined, is the lower opening of the canal. 

 Its upper orifice, which will be seen at a later stage, is termed th^' 

 internal abdominal rinff. The dii'ection of the canal is oblique down- 

 wards and inwards, and it is slightly curved wath the concavity forwards. 

 Introduce the finger into the canal and press on the posterior wall. 

 This, it will be seen, is formed by the reflected portion of the external 

 oblique tendon — in other words, by Poupart's ligament. Kotate the 

 hand, and press the finger on the anterior wall, at the same time separ- 

 ating the edges of the external abdominal ring. The anterior wall will 

 be seen and felt to be formed by muscular substance, viz., by the 

 muscular part of the internal oblique. 



The canal gives passage in the male to the spermatic cord, the external 

 pudic vessels, and the inguinal nerves. In the female it is much 

 smaller, and transmits the corresponding vessels and nerves. 



The Spermatic Cord. See page 278. 



The External Pudic Artery (Plate 39) is one of the terminal 

 divisions of the prepubic. In the inguinal canal it descends posterior 

 and internal to the spermatic cord. After its emergence it divides into 

 the subcutaneous abdominal arteiy, and the anterior dorsal artery of 

 the penis. In the mare the latter branch is represented by the mammary 

 artery. 



