214 MUSCLES OF THE ABDOMEN. 



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 (oUiquus interims abdominis ascendens) 

 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 pectineal 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 aponeurosis 

 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 pectineal 

 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 the in- 

 ternal oblique and transversalis. This structure corresponds 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 passage 

 some fibres are given off from the lower border of the muscle, which ac- 

 company 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. 



The CREMASTER, considered as a distinct muscle, arises from the mid- 

 dle of Poupart's ligament, and forms a series of loops upon the spermatic 

 cord. A few of its fibres are inserted into the tunica vaginalis, the rest 

 ascend along the inner side of the cord, to be inserted, with the conjoined 

 tendon, into the pectineal line of the os pubis. 



Relations. The internal oblique is in relation, by its external surface, 

 with the external oblique, latissimus dorsi, spermatic cord, and external 

 abdominal ring. By its internal surface, with the transversalis muscle, 

 the fascia transversalis, the internal abdominal ring, and spermatic cord. 

 By its lower and arched border, with the spermatic cord, forming the 

 upper boundary of the spermatic canal. 



The cremaster is in relation, by its external surface, with the aponeuro- 

 sis of the external oblique and intercolumnar fascia ; and by its internal 

 surface, with the fascia propria of the spermatic cord. 



The internal oblique muscle is to be removed by separating it from its 

 attachments to the ribs above, and to the crest of the ilium and Poupart's 

 ligament below. It should be divided behind by a vertical incision, ex- 

 tending from the last rib to the crest of the ilium, as its lumbar attachment 

 rannot at present be examined. The muscle is then to be turned for- 



