MUSCLES OF THE BODY. 155 
68, ~). Inner surface with the transversus abdominis (Fig. 
69, 7), 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. —(1) 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 
/nsertion in the linea alba. 
Relations.—Outer surface with the internal oblique (Fig. 
73, 0) and the rectus abdominis (Fig. 73, £), dorsad also with 
the longissimis dorsi (Fig. 69, f). Inner surface with a thin 
fascia covering the peritoneum and ventrocaudad with the 
rectus (Fig. 73, #). 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, 4).—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 
