

THE INTERNAL OBLIQUE MUSCLE. 



331 



upper border of the posterior lamina is attached to the margins of the seventh and 

 eighth rib-cartilages, as well as to the ensiform process. This division of the 

 aponeurosis into two layers stops short a little above half-way between the umbili- 

 cus and the pubis and about on a level with the anterior superior spine of the ilium, 

 the aponeurosis below that spot remaining undivided, and along with that of the 

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

 The deficiency thus resulting in the posterior wall of the sheath of the rectus is 

 marked superiorly by a more or less well defined lunated edge, the^ concavity of 

 which looks downwards towards the pubis the semilunar fold of Douglas (fig. 294). 



Relations. The internal oblique muscle is almost entirely covered by the external oblique. 

 The hindmost part of the muscle, arising from the lumbar fascia, is under cover of the latis- 

 simus dorsi, and a small part is frequently exposed between the latissimus and the external 

 oblique, when those muscles fail to meet at their iliac origins (p. 329). 



Fig. 293. DIAGRAM OP A TRANS-- 

 VERSE SECTION OP THE WALL 

 OP THE ABDOMEN, TO SHOW 

 THE CONNECTIONS OP THE LUM- 

 BAR FASCIA, AND THE SHEATH 

 OP THE RECTUS MUSCLE. (Allen 



Thomson. ) 3 



A, at the level of the third 

 lumbar vertebra ; B, the fore part, 

 at a few inches above the pubis. 



a, spinous process, 6, body of 

 the third lumbar vertebra ; 1, ex- 

 ternal oblique muscle ; 2, internal 

 oblique ; 3, transversalis ; 4, a 

 dotted line to mark the position 

 of the transverslis fascia ; 5, 5, in 

 A, anterior and posterior parts of 

 the sheath of the rectus, formed 

 by the aponeurosis of the internal 

 oblique splitting at the outer edge 

 of the muscle 2' ; 6, rectus abdo- 

 minis ; 7, anterior layer of the 

 lumbar fascia, passing in front of 

 the quadratus lumborum to the 

 anterior surface of the transverse 

 process ; 8, psoas magnus and 

 parvus muscles ; 9, 9', erectores 

 spinae muscles ; 9 + , middle layer 



of the lumbar fascia (posterior aponeurosis of the transversalis) passing to the extremity of the 

 transverse process ; 10, 10 + , posterior layer of the lumbar fascia, connected with the latissimus dorsi 

 and serratus posticus inferior : in A, at the sheath of the rectus, the aponeurosis of the external oblique 

 is seen to unite in front with the sheath, while that of the transversalis is seen uniting with it behind : 

 in B, the section is taken below the semilunar fold of Douglas, and all the tendons pass in front of the 

 rectus at 5' ; the + near this, and in a similar place in A, marks the middle line, and the place of the 

 union of the several aponeuroses in the linea alba. 



Varieties. A fibrous band or inscription is not uncommonly seen in the upper part of this 

 muscle, prolonged forwards from the point of the tenth or eleventh rib, and a slender carti- 

 laginous slip, separate from that of the rib, has been seen lying in this inscription. An 

 additional slip of insertion, into the ninth costal cartilage, is occasionally present. The por- 

 tion of the muscle arising- from Poupart's ligament may be separated by an interval from the 

 iliac origin (Solger). 



The fold of Douglas is often indistinct, the hinder layer of the sheath of the rectus end- 

 ing indefinitely in scattered tendinous bundles united to the transversalis fascia. The 

 deficiency at the lower part of the aponeurotic sheath posteriorly is regarded by G-egenbaur as 

 due to the position of the urinary bladder in early life, which is in a measure embedded in the 

 anterior abdominal wall, and the upward extent of which is said to correspond to the semi- 

 lunar folds. Solger, with more probability, explains the deficiency as the result of differences 

 in the degree of tension to which the aponeurosis is subject in its upper and lower parts in the 

 movements of respiration and during the contraction of the abdominal muscles, the portions 

 of the obliquus internus and transversalis below the fold of Douglas being weaker, and having 



