MUSCLES OF THE BODY. 155 



68, /). Inner surface with the transversus abdominis (Fig. 



69, /) , and by its ventral tendon with the rectus. 

 Action. Compressor of the abdomen. 



M. transversus abdominis (Fig. 69, /). A thin sheet 

 covering the whole surface of the abdomen and lying beneath 

 the internal oblique. Its fibres are nearly transverse. 



Origin. (i) By fleshy fibres or by a thin aponeurosis from 

 the cartilages of all the false and floating ribs, by interdigitation 

 with the fibres of the diaphragm. (2) From the tips of all the 

 lumbar transverse processes. (3) From the ventral border of 

 the ilium. (4) From the dorsal and middle of the three crural 

 arches, where it may blend partly with the internal oblique. 

 The muscle is continuous craniad with the transversus thoracis 

 muscle. Near the lateral border of the rectus abdominis the 

 'muscle ends in a thin aponeurosis of insertion which is con- 

 tinued (its fibres having the direction of the muscle-fibres) to 

 the 



Insertion in the linea alba. 



Relations. Outer surface with the internal oblique (Fig. 

 73, o] and the rectus abdominis (Fig. 73, k), dorsad also with 

 the longissimis dorsi (Fig. 69, /). Inner surface with a thin 

 fascia covering the peritoneum and ventrocaudad with the 

 rectus (Fig. 73, K). The dorsal edge of the muscle touches 

 the iliopsoas and longissimus dorsi ; the ventral edge touches 

 the muscle of the opposite side. 



Action. Constrictor of the abdomen. 



M. rectus abdominis (Fig. 73, k). A rather thick, flat 

 muscle which lies near the median ventral line separated by 

 the linea alba from its fellow of the opposite side and stretching 

 from the pubis to the first costal cartilage. Opposite the first 

 lumbar vertebra it is approximately four centimeters wide. It 

 narrows at both ends. 



Origin by a strong tendon from the tubercle of the pubis. 

 The muscle passes craniad at first between the peritoneal fascia 

 and the transversus aponeurosis, then in the sheath formed by 

 the internal and external oblique and the transversus aponeuro- 

 sis. It emerges from the sheath opposite the xiphoid process 

 and passes ventrad of the costal cartilages. Between the third 



