LINEA ALBA. QUADRATUS LUMBORUM. 335 



and even to the third rib. On the other hand, the slip of insertion into the fifth cartilage may 

 be wanting. 



The tendinous intersections have been regarded as indications of the abdominal ribs of 

 some of the lower animals ; they are rather vestiges of the septa between the original vertebral 

 myotomes. They sometimes extend outwards from the rectus, and penetrate partially into the 

 internal oblique. 



The pyramidalis is a small muscle resting on the lower part of the rectus, in 

 the sheath of which it is contained. It arises by short tendinous fibres from the 

 front of the pubis below the rectus, and, becoming narrower as it ascends over the 

 lower third of the interval between the umbilicus and pubis, is inserted into the 

 linea alba. 



Varieties. This muscle varies greatly in size, and it is often absent on one or both sides, 

 in which case the size of the lower part of the rectus is increased : in some instances it has 

 been found to be double. 



The linea alba is a white fibrous structure extending perpendicularly in the 

 middle line from the ensiform process to the pubis. This tendinous band is formed 

 by the union of the aponeuroses of the two oblique and the transverse muscles, the 

 tendinous fibres being continued in a decussating manner from one side to the other. 

 It is broader superiorly than inferiorly, and a little below the middle it is widened out 

 into a circular flat space, in the centre of which is situated the cicatrix of the 

 umbilicus. At the lower end, where the linea alba becomes narrow and less marked, 

 and passes in front of the conjoined inner heads of the recti muscles to the symphysis 

 pubis, there is detached from it posteriorly a small band of longitudinal fibres, the 

 adminkulum Unece albce, which spreads out below into a triangular expansion fixed 

 on each side to the upper border of the body of the pubis behind the outer head of 

 the rectus. At the upper end there are also a few longitudinal fibres descending 

 from the ensiform process. The linea alba is much increased in breadth when the 

 abdomen is distended during pregnancy or from disease. 



The linea semilunaris is a curved linear depression on each side of the front of 

 the abdomen, situated along the outer border of the rectus muscle, and appearing 

 as a white line on the surface of the aponeurosis of the external oblique. It 

 corresponds to a narrow portion of the aponeurosis of the internal oblique, 

 between its division to form the sheath of the rectus internally, and the termina- 

 tion of the fleshy fibres of the muscle externally. The lines transverse 

 are cross lines, corresponding to, and produced by, the tendinous intersections 

 of the rectus. 



The quadratus lumborum (fig. 248, p. 244) is a quadrilateral muscle, some- 

 what broader below than above, placed between the last rib and the pelvis, close to 

 the vertebral column. It arises below by fleshy and tendinous fibres from the ilio- 

 lumbar ligament and from the iliac crest for about two inches, behind and external 

 to the attachment of that ligament, and on the inner side from the transverse 

 processes of two, three or four lumbar vertebrae, by tendinous and fleshy slips, the 

 fibres of which ascend on the anterior surface of the muscle. It is inserted into the 

 lower border of the last rib for about half its length, and into the transverse 

 processes of the upper four lumbar vertebrae, by tendinous slips placed generally 

 behind the slips arising from those processes. 



Relations. The quadratus lumborum is contained in a sheath formed by the anterior and 

 middle layers of the lumbar fascia. Its anterior surface is overlapped by the psoas, and upon 

 it rests the kidney, while the ascending or descending colon lies in front of its outer border. 

 The inner border is intimately connected with the lateral intertransverse muscles. 



Varieties. The number of the points of insertion of this muscle to the vertebrse, and the 

 extent of its connection with the last rib, vary in different instances. It is sometimes attached 

 to the body or transverse process of the last dorsal vertebra. 



