246 THE ABDOMEN AND PELVIS 



(f. transversalis) is continuous with the layer on the under 

 surface of the diaphragm ; (2) from the lumbo-dorsal fascia ; 

 and (3) from the iliac crest and the lateral third of the inguinal 

 ligament. The general direction of the fibres is horizontal, but 

 the lowest fibres turn downwards to be inserted into the pecten 

 pubis (ilio-pectineal line) where they take part in the formation 

 of the falx inguinalis (conjoined tendon). The rest of the muscle 

 forms an aponeurosis which gains attachment to the linea alba. 

 This aponeurosis is extremely narrow above, but it gradually 

 widens below. 



The Eectus Abdominis muscle arises from the pubis and 

 extends upwards in the interval between the linea alba and the 

 linea semilunaris (p. 239). It is inserted into the anterior 

 aspects of the fifth, sixth, and seventh costal cartilages. Irregular 

 tendinous intersections cross the muscle, one at the umbilicus, 

 a second at the xiphoid process, and a third midway between 

 the other two. They are known as the Linece Transverse? , and 

 are strongly adherent to the anterior wall of the rectus sheath. 



The sheath of the rectus abdominis is a strong but incomplete 

 aponeurotic envelope, which is formed by the aponeuroses of the 

 three lateral abdominal muscles. It is differently constituted 

 in its upper and lower parts. 



(a) Above the level of the midpoint between the umbilicus and 

 the symphysis pubis. The aponeurosis of the internal oblique 

 splits into an anterior and a posterior lamella at the lateral 

 margin of the rectus. The anterior layer blends with the 

 aponeurosis of the external oblique, and forms the anterior wall 

 of the sheath, while the posterior layer blends with the aponeurosis 

 of the transversus to form the posterior wall. Where the 

 muscle rests on the costal cartilages near its insertion, the 

 posterior wall of its sheath is deficient, as the internal oblique 

 and transversus abdominis do not pass upwards beyond the 

 seventh costal cartilage. In its upper part the posterior wall 

 is not entirely aponeurotic, as, owing to the narrowness of its 

 aponeurosis, the upper fleshy fibres of the transversus lie behind 

 the rectus abdominis and almost reach the linea alba. 



(b) Below the level of the midpoint between the umbilicus and 

 symphysis pubis. In this region the sheath of the rectus is 

 formed anteriorly by the blended aponeuroses of the external 

 oblique, internal oblique, and transversus. The posterior wall 

 terminates in a free crescentic lower margin the linea semi- 

 circularis (semilunar fold of Douglas) at the level indicated 



