190 MUSCLES OP THE ABDOMEN. 



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 down- 

 wards, 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, 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 pec- 

 tineal line 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 it is insuf- 

 ficient to resist the pressure from within, and becomes forced through 

 the external ring: it then forms the distinctive covering of direct in- 

 guinal hernia. 



The spermatic cord passes beneath the arched border of the in- 

 ternal oblique muscle, between it and Poupart's ligament. During 

 its passage 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 crem aster 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 

 middle 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 in- 

 serted, with the conjoined tendon, into the pectineal line of the os 

 pubis. 



Relations. The internal oblique is in relation by its external sur- 

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

 external abdominal ring. By its internal surface with the trans- 

 versalis 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 

 aponeurosis of the external oblique and inter-columnar 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 the three inferior lumbar spinous processes and all those of the sacrum. G. 



