MUSCLES OF THE TRUNK. 241 



doubling of this aponeurosis into two layers. One of these leaves descends on 

 the internal muscles of the thigh to constitute the crural aponeurosis 

 (Mg. 116, 11); while the other is reflected upwards and forwards, to enter 

 the abdominal cavity ; this reflected leaf of the great oblique aponeurosis is 

 named the crural arch (ligament of Poupart or Fallopius). (Fig. 108, b.) 



Near, the prepubic tendon of the abdominal muscles, and immediately 

 before its division into two leaves, the aponeurosis of the external oblique is 

 pierced by a large oval aperture (Fig. 116, 5), the inferior orifice of the 

 canal through which passes the cord of the testicle in the male, and the 

 mammary vessels in the female. This channel has been named the inguinal 

 canal. 



The description of the femoral aponeurosis, the crural arch, and the 

 inguinal ring — a necessary complement of the great oblique muscle — will be 

 given hereafter. 



Relations of the Great Oblique Muscle. — By its superficial face, the 

 external oblique responds to the sterno-trochineus and the abdominal tunic, 

 which latter separates it from the skin and the panniculus. By its deep face, 

 it is related to the ribs, into which it is inserted, as well as with their carti- 

 lages, the corresponding intercostal muscles, the small oblique, and the great 

 straight muscle. The latter even appears to be attached, through the 

 anterior moiety of its external border, to the fleshy portion of the great 

 oblique, by means of a slight lamina of yellow elastic tissue, which covers, 

 to a small extent, the deep face of the two muscles. 



Action. — The external oblique, in contracting, compresses the abdominal 

 viscera, flexes the vertebral column, and acts as an expiratory muscle. (By 

 its compression on the abdominal viscera it concurs in the acts of defecation, 

 micturation, and parturition.) 



Internal Cbuhal Aponeurosis. — This fibrous lamina descends from the 

 plicature of the flank on the patella and the inner surface of the leg. 

 Outwardly, it is confounded with the aponeurosis of the fascia lata; in- 

 wardly, it degenerates into cellular tissue. It covers the long adductor of 

 the leg, part of the short adductor, the vastus internus, and the crural vessels 

 at their exit from the abdominal cavity. 



CrtieaI; Arch. — As already mentioned, this is the reflected leaf of the 

 great oblique aponeurosis, and is also named the ligament of Fallopius and 

 Pouparffs ligament. It is a wide, flat band, attached by its extremities to the 

 external angle of the ilium and the anterior border of the pubis. Its 

 anterior face (Fig. 108, b) forms, inwardly, the posterior wall of the inguinal 

 canal ; it gives attachment, outwardly, to the posterior fibres of the small 

 oblique muscle. Its posterior face, appHed against the superior extremity of 

 the patellar muscles, the long adductor of the leg, the pectineus, and the 

 crural vessels on their leaving the abdomen, embraces all these parts as in a 

 vast arch, and from this peculiarity it derives its name. Its superior border 

 is inserted, for its external half, into the Imnbo-iliac aponeurosis. In its 

 middle part it is much thinner, and is prolonged to the external surface of 

 the long adductor muscle of the leg and the iliac fascia, to be at last mixed 

 up with the latter. Within the pectineal insertion of the small psoas 

 muscle, it forms the anterior margin of the crural ring : a triangular orifice 

 circumscribed on the other side by the anterior border of the pubis, the 

 iliacus, and the long adductor of the leg, and through which pass the crural 

 vessels as they leave the abdomen by the crural arch.^ The inferior border 



' This orifice is covered by a very thin aponeurotic layer, which is prolonged, above, 

 on the crural vessels, behind, into the pelvic cavity, and which appears to be continuous. 



