TRANSVERSUS ABDOMINIS 



435 



Action. — To depress the ribs in expiration. 



Relations. — The sternum, the costal cartilages, internal intercostal muscles, and the internal 

 mammary vessels lie in front and the pleura and pericardium behind the muscle. 



Variations. — It is an exceedingly variable muscle, both in the extent of its attachments 

 and in the development of the individual fasciculi. The fasciculi vary in number from one to 

 six. With this muscle Eisler would class the subcostal muscles and those portions of the internal 

 intercostal muscles which lie internal to the intercostal nerves. 



The transversus abdominis (figs. 386, 390). — Origin. — Directly from — (1) the inner side 

 of the cartilages of the lower six ribs by dentations which interdigitate with the attachments of 

 the diaphragm; (2) the internal lip of the iliac crest and lateral half of the inguinal ligament; 

 and (3) through an aponeurosis from the lumbo-dorsal fascia. 



Structure and insertion. — The fibre-bundles give rise to a broad, thin belly and take a nearly 

 transverse course across the inner side of the abdominal wall. The most distal fibres, however, 

 are inclined obhquely toward the pubis. The fleshy portion of the muscle terminates in a 

 strong aponeurosis along a curved line, which extends above well under the rectus and emerges 



Fig. 390. — Transversus Abdominis and Sheath of Rectus. 



External intercostal 



Internal intercostal-r — ^^^z7 1 



Posterior portion of sheathi^^-j 



of rectus t,~= 



Transversus abdominis 



Rectus abdominis 



Iliacus 



Transversalis fascia 



Falx inguinalis 



Inguinal ligament 



Lacunar ligament 



Serratus anterior 



Ventral layer of lumbo- 

 dorsal fascia 



lateral to the rectus opposite the umbilicus, whence it extends toward the middle of the inguinal 

 ligament. In the upper two-thirds of the abdomen the aponeurosis extends behind the rectus 

 to the linea alba and fuses with the inner lamina of that of the internal oblique. In the lower 

 third of the abdomen it extends in front of the rectus to the linea alba, and is here also fused 

 with the aponeurosis of the internal oblique. Some of the fibres are continued into the aponeu- 

 rosis of the muscle of the opposite side. The lower attachment of the muscle is somewhat 

 more complex. The fibre-bundles here bend around the spermatic cord, on the medial side of 

 which they are spread out to be attached to the lacunar (Gimbernat's) ligament and pectineal 

 fascia, the pubis, and the sheath of the rectus. The attachment to the lacunar ligament and 

 pectineal fascia takes place by means of an aponeurotic band, the more lateral fibres of which 

 are dense and curve below the spermatic cord to the lacunar ligament and the pectineal fascia 

 below this. This band is called the interfoveolar ligament. It is composed partly of bundles of 

 fibres prolonged from the aponeurosis of the opposite transversus, and bounds the abdominal ring 

 medially and below. Medially the transversus is united to the upper part of the os pubis, and 

 to the sheath of the rectus by an aponeurotic band, the falx inguinalis (conjoined tendon). 

 Between the interfoveolar ligament and the falx inguinalis the transversalis fascia forms the 

 posterior wall of the inguinal canal. In this area a detached band of muscle-fibres is sometimes 

 found. This is called the musculus interfoveolaris. 



Nerve-supply. — The transversus is suppHed with nerves by the last five or six thoracic and 



