INTEENAL OBLIQUE MUSCLE. 317 



eord from the margin of the opening, are prolonged upon that structure 

 as a delicate fascia, named intercolumnar fascia. The intercolumnar 

 fibres may be regarded as the lowest of a series of tendinous fibres, 

 which cross the aponeurosis of the external oblique muscle somewhat 

 obliquely over a considerable extent of its surface, and the strongest of 

 which proceed from near the superior spine of the ilium and upper part 

 of Poupart's ligament. 



Varieties. — This muscle chiefly varies in respect to the number of attachments 

 to the ribs, the slips from the eighth and ninth ribs being occasionally double, 

 while those from the eleventh and twelfth are sometimes wanting. Besides the 

 usual sliiJ to the pectoralis major, a slip is sometimes found to the serratus 

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

 from the three lowest ribs to the crest of the ilium. (Macalister.) 



The obliqtms abdominis intermis 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, from the iliac 

 crest for two-thirds of its length, and by some fibres fi'om the posterior 

 aponeurosis of the transversalis muscle, in the angle between the crest 

 of the ilium and the outer margin of the erector spinse muscle. From 

 those attachments the fibres, spreading somewhat, pass to be inserted as 

 follows : the most posterior fibres pass upwards and forwards to the 

 lower margins of the cartilages of the last four ribs, where they are 

 inserted in the same plane with the internal intercostal muscles ; those 

 arising further forwards from the crest of the ilium pass, the upper more 

 obliquely, and the rest more horizontally, forwards to end in an aponeu- 

 rosis in front of the abdomen ; those from the front part of the crest 

 extend horizontally inwards to the same aponeurosis ; while the fibres 

 from Poupart's ligament, usually paler than the rest, arch downwards 

 and inwards over the spermatic cord, or the rouud ligament of the 

 uterus, and end in tendinous fibres common to them and the lower 

 part of the transversalis muscle, and hence known as the conjoined 

 tendon of these muscles ; through the medium of this tendon they are 

 attached to the front of the pubis, and for some distance along the 

 pectineal line, behind and to the outside of Gimbernat's ligament. The 

 spermatic cord and round ligament pass under the arched lower border 

 of the internal oblique and transversalis muscles through the internal 

 or deep abdominal ring. 



The aponeurosis of the internal oblique may be regarded as the ex- 

 panded tendon of the muscle continued forwards and inwards : it extends 

 from the margin of the thorax to the pubis, and is wider at the upper 

 than at the lower end. At the outer border of the rectus muscle 

 this structure divides into two layers, one passing before, the other 

 behind, that muscle ; and the two reunite at its inner border, so as to en- 

 close it in a sheath. The anterior layer, as akeady mentioned, becomes 

 inseparably united with the aponeurosis of the external oblique muscle, 

 and the posterior layer is similarly incorporated with that of the trans- 

 versalis. The upper border of the posterior lamina is attached to the 

 margins of the seventh and eighth ribs, as well as to the ensiform 

 cartilage. Tliis division, however, of the aponeurosis into layers stops 

 short a little nbove half way between the umbilicus and the pubis, the 

 aponeurosis below that level remaining undivided, and along with that 

 of the transversalis muscle to which it is united, passing wholly in front 



