OBLIQUUS INTERNUS ABDOMINIS. 213 



*The pouch of inguinal hernia, in passing through this opening, re- 

 ceives the inter-columnar fascia, as one of its coverings. 



Relations. By its external surface with the superficial fascia and 

 integument, and with the cutaneous vessels and nerves, particularly the 

 superficial epigastric and superficial circuraflexa ilii vessels. It is ge- 

 nerally overlapped posteriorly by the latissimus dorsi. By its internal 

 surface with the internal oblique, the lower part of the eight inferior 

 ribs and intercostal muscles, the cremaster, the spermatic cord in the 

 male, and the round ligament in the female. The upper border of the 

 external oblique is continuous with the pectoralis major. 



The external oblique is now to be removed by making an incision 

 across the ribs, just below its origin, to its posterior border ; and another 

 along Poupart's ligament and the crest of the ilium. Poupart's liga- 

 ment should be left entire, as it gives attachment to the next muscles. 

 The muscle may then be turned forwards towards the linea alba, or 

 removed altogether. 



The INTERNAL OBLIQUE MUSCLE (obliquus internus abdominis^ as- 

 cendens\ is the middle flat muscle of the abdomen. It arises from 

 the outer half of Poupart's ligament, from the middle of the crest of 

 the ilium for two-thirds of its length, and by a thin aponeurosis from 

 the spinous processes of the lumbar vertebrae. Its fibres diverge from 

 their origin, so that those from Poupart's ligament curve downwards, 

 those from the anterior part of the crest of the ilium pass transversely, 

 and the rest ascend obliquely. The muscle is inserted into the pecti- 

 rieal line and crest of the os pubis, linea alba, and lower borders of the 

 five inferior ribs. 



Along the upper three fourths of the linea semilunaris, the aponeu- 

 rosis of the internal oblique separates into two lamellae, which pass 

 one in front and the other behind the rectus muscle to the linea alba, 

 where they are inserted ; along the lower fourth, the aponeurosis 

 passes altogether in front of the rectus without separation. The 

 two layers, which thus enclose the rectus, form for it a partial sheath. 



The lowest fibres of the internal oblique are inserted into the pecti- 

 neal line of the os pubis in common with those of the transversalis 

 muscle. Hence the tendon of this insertion is called the conjoined 

 tendon of tlie internal oblique and transversalis. This structure corres- 

 ponds with the external abdominal ring, and forms a protection to what 

 would otherwise be a weak point in the abdomen. Sometimes the 

 tendon is insufficient to resist the pressure from within, and becomes 

 forced through the external ring ; it then forms the distinctive covering 

 of direct inguinal hernia. 



The spermatic cord passes beneath the arched border of the internal 

 oblique muscle, between it and Poupart's ligament. During its pas- 

 sage some fibres are given off from the lower border of the muscle, 

 which accompany the cord downwards to the testicle, and form loops 

 around it: this is the cremaster muscle. In the descent of oblique 

 inguinal hernia, which travels the same course with the spermatic 

 cord, the cremaster muscle forms one of its coverings. 



