THE EXTERNAL OBLIQUE MUSCLE. 329 



ture\ and is formed by the separation of -the fibres composing the lower and inner 

 angle of the aponeurosis from the innermost part of Poupart's ligament. The 

 direction of the opening is obliquely upwards and outwards conformably to the 

 direction of the principal fibres of the aponeurosis ; its base is formed by the pubic 

 crest, and its sides by the two sets of diverging fibres called i\LQ pillars. The upper 

 or internal pillar is flat and straight, and is attached to the anterior surface of the 

 symphysis pubis, decussating with the corresponding fibres on the opposite side : 

 the lower or external pillar is in its upper part also flat and thin, but its lower part, 

 which is formed by the inner end of Poupart's ligament, is thick and prismatic, and 

 curves strongly inwards to its termination at the pubic spine. 



While the mesial attachment of Poupart's ligament takes place mainly into the 

 pubic spine, the deepest fibres of that band are sent backwards to be fixed to the 

 innermost part of the ilio-pectineal line for a distance of about three-quarters of an 

 inch, constituting a triangular layer which is termed Gimbernafs ligament, and which 

 presents upper and lower surfaces, and a concave external margin, the latter being 

 free and forming the inner boundary of the femoral ring. Some of the fibres of 

 Gimbernat's ligament and of the outer pillar of the ring are usually attached only 

 indirectly to the bone ; and these are reflected upwards and inwards beneath the 

 spermatic cord, becoming incorporated with the lowest part of the front of the 

 sheath of the rectus, and reach the middle line where they interlace with the fibres 

 of the opposite side. They form a variably developed layer, placed behind the lower 

 part of the external abdominal ring and its inner pillar, and known as the triangular 

 fascia. 



On the surface of the aponeurosis, especially in its lower part, are seen slender 

 bundles of fibres crossing transversely and binding together its principal oblique 

 fibres. These are the intercolumnar fibres, and they are most developed in the 

 neighbourhood of the outer third of Poupart's ligament, and the anterior superior 

 iliac spine. They extend across the upper part of the external abdominal ring, 

 closing to a greater or less extent the angular interval left between the diverging 

 pillars, and from them a thin membrane is prolonged downwards upon the spermatic 

 cord, known as the intercolumnar or spermatic fascia. The external abdominal ring 

 thus acquires a somewhat oval form, and its size varies in proportion to the degree 

 of development of these fibres. In the male the opening has an average length of 

 an inch or a little, more, with a breadth of half as much. In the female it is 

 usually much smaller. 



Relations. The external oblique muscle is superficial with, the exception of a small part 

 at its posterior border which is overlapped by the latissimus dorsi. It lies upon the internal 

 oblique and the lower ribs with their cartilages and the intervening intercostal muscles. The 

 origins of the external oblique and latissimus sometimes meet at the iliac crest, but more 

 frequently a small interval is left, and the free portion of bone forms the base of a triangular 

 *pace between the two muscles triangle of Petit, in which a hernia (lumbar hernia) has been 

 seen to protrude. 



Varieties. The external oblique varies chiefly in the number of its attachments to the 

 ribs. Absence of the highest or lowest digitation is not uncommon ; on the other hand, one 

 or more slips may be doubled, most frequently those from the eighth and ninth ribs ; or an 

 additional slip may arise from the lumbar aponeurosis below the last rib. Besides the con- 

 nection with the pectoralis major, some fibres are occasionally continued into the serratus 

 .magnus. The muscle has also been found double, the deeper accessory portion passing from 

 some of the lower ribs to the crest of the ilium or to Poupart's ligament. 



The obliquus interims abdominis muscle, placed under cover of the external 

 oblique, arises by fleshy fibres from the external half or two-thirds of the deep surface 

 of Poupart's ligament, by short tendinous fibres from the middle ridge of the iliac 

 crest for two-thirds of its length ; and by some fleshy fibres again from the posterior 

 aponeurosis of the transversalis muscle (lumbar fascia) in the angle between the 



