436 THE MUSCLES AND FASCIA 



Transversalis; and these, joining again at its inner border, are inserted into the 

 linea alba. This arrangement of the aponeuroses exists along the upper three- 

 fourths of the muscle; at the commencement of the lower fourth, the posterior 

 wall of the sheath terminates in a thin curved margin, the semilunar fold of Douglas 

 (linea semicircularis) (Fig. 325), the concavity of which looks downward toward 

 the pubes; the aponeuroses of all three muscles pass in front of the Rectus without 

 any separation. A very thin aponeurotic layer does pass behind the lower one- 

 fourth of the muscle, but it is trivial as compared with the thickness of the layer 

 behind the upper three-fourths of the muscle. This sudden thinning causes the 

 semilunar fold of Douglas. The extremities of the fold of Douglas descend as 

 pillars to the os pubis. The inner pillar is attached to the symphysis pubis; 

 the outer pillar passes downward as a distinct band on the inner side of the internal 

 abdominal ring to join with the outer fibres of the conjoined tendon, and assist 

 in forming the ligament of Hesselbach (ligamentum interfoveolare) (Fig. 322). 

 There its fibres divide into two sets, internal and external; the internal fibres are 

 attached to the ascending ramus of the os pubis; the external fibres pass to the 

 psoas fascia, to the deep surface of Poupart's ligament, and to the tendon of the 

 Transversalis on the outer side of the ring. The Rectus muscle, in the situ- 

 ation where its sheath is deficient, is separated from the peritoneum by the trans- 

 versalis fascia. Since the tendon of the Internal oblique and the Transversalis 

 only reach as high as the costal margin, it follows that above this level the sheath 

 of the Rectus is also deficient behind, the muscle resting directly on the cartilages 

 of the ribs, being covered merely by the aponeurotic tendon of the External 

 oblique. The convex outer border of the Rectus muscle corresponds to the linea 

 semilunaris. 



The Pyramidalis (m. pyramidalis) is a small muscle, triangular in shape, 

 placed at the lower part of the abdomen, in front of the Rectus, and is contained 

 in the same sheath. It arises by tendinous fibres from the front of the os pubis 

 and the anterior pubic ligament; the fleshy portion of the muscle passes upward, 

 diminishing in size as it ascends, and terminates by a pointed extremity, which is 

 inserted into the linea alba, midway between the umbilicus and the os pubis. This 

 muscle is sometimes found wanting on one or both sides; the lower end of the 

 Rectus then becomes proportionately increased in size. Occasionally it has been 

 found double on one side, or the muscles of the two sides are of unequal size. 

 Its length varies slightly. 



Besides the Rectus and Pyramidalis muscles, the sheath of the Rectus contains the superior 

 and deep epigastric arteries, the terminations of the lumbar arteries and of the lower intercostal 

 arteries and nerves. 



Nerves. The abdominal muscles are supplied by the lower intercostal nerves. The Trans- 

 versalis and Internal oblique also receive filaments from the hypogastric branch of the ilio- 

 hypogastric and sometimes from the ilioinguinal. The Cremaster is supplied by the genital 

 branch of the genitofemoral. The Pyramidalis is supplied by the twelfth thoracic nerve 



The linea alba (Figs. 326 and 327) is a tendinous raphe seen along the middle line of the 

 abdomen, extending from the ensiform cartilage to the superior pubic ligament, to which it is 

 attached. It is placed between the inner borders of the Recti muscles, and is formed by the 

 blending of the aponeuroses of the Obliqui and Transversales muscles. It is narrow below, 

 corresponding to the narrow interval existing between the Recti, but broader above, as these 

 muscles diverge from one another in their ascent ; it becomes of considerable breadth when there 

 is great distention of the abdomen from pregnancy or from ascites. It presents numerous aper- 

 tures for the passage of vessels and nerves; the largest of these is the umbilicus (Fig. 329). The 

 umbilicus is a fibrous ring formed by the fibres of the aponeurosis of the linea alba; in the 

 fetus it transmits the umbilical vein, the two hypogastric arteries, the allantoic duct, and the 

 vitello-intestinal duct; but in the adult the aperture is filled with scar tissue and is obliterated; 

 the resulting cicatrix is stronger than the neighboring parts; hence umbilical hernia occurs in the 

 adult near the umbilicus, while in the fetus it occurs at the umbilicus. The remains of the fetal 

 structures are cord-like in character; and they diverge from the umbilicus within the abdomen. 



