INTERNAL OBLIQUE MUSCLE. 269 



Parts covered by the external oblique (fig. 99). Beneath the external Parts 

 muscle are the internal oblique, with parts of the ribs and intercostal e 

 muscles. At the lower part of the abdomen the muscle conceals oblique, 

 the spermatic cord and the branches of the lumbar plexus in the 

 abdominal wall. 



The INTERNAL OBLIQUE MUSCLE (fig. 99, A) IS fleshy at the side Internal 



and aponeurotic in front, like the preceding ; but its fibres (except 



the lowest) ascend across those of the external oblique. The muscle 



arises from the outer half of Pou part's ligament, from the anterior origin from 



two-thirds of the crest of the ilium (fig. 47, p. 113), and from the pelvis ; 



tendon of the transversalis muscle (fascia lumborum, c) in the 



interval between that bone and the last rib. The fibres diverge 



on the abdomen to their destination : The upper ones ascend, and insertion 



have a fleshy insertion into the cartilages of the last three ribs, j^Jind 



where they join the internal intercostal muscles of the lowest two lineaaiba. 



spaces. The remaining fibres pass forwards, with varying degrees of 



obliquity, to end in an aponeurosis. 



The aponeurosis of the muscle extends from the thorax to the Aponeurosia 

 pelvis, and is broader above than below. For the most part it is enclose 

 split to encase the rectus (as will be seen when that muscle is g^ us t ' 

 exposed) ; but in the lower half of the space between the umbilicus below ; 

 and pubis it is undivided, and lies altogether in front of that muscle. 

 Along the middle line the two layers are united together, as well as 

 with those of the opposite side, in the linea alba. Superiorly the 

 aponeurosis is arranged in the following manner : for a short attachments 

 distance before it divides, it is fixed to the ninth costal cartilage ; to est> 

 and the posterior of the layers into which it divides continues this 

 attachment along the eighth and seventh cartilages to the ensiform 

 process ; while the anterior is prolonged over the chest, blending 

 with the aponeurosis of the external oblique. Inferiorly its fibres 

 become more distinct and are inserted into the front of the pubis, and and pelvis. 

 into the pectineal line for half an inch behind the attachment of 

 Gimbernat's ligament. This lowest part of the aponeurosis is 

 blended with that of the underlying transversalis to form what 

 will be described as the conjoined tendon of the two muscles. 



delations. The muscle is covered by the external oblique muscle. Parts in 

 It is attached on all sides, except between Poupart's ligament and 

 the pubis, where it arches over the spermatic cord, and has the oblique, 

 cremaster muscle continuous with it. The parts covered by the 

 internal oblique will be seen when the muscle is reflected. 



Action. Both muscles depress the ribs, and assist in forcing back Use of both 

 the viscera of the. belly after they have been protruded by the 

 descent of the diaphragm. 



One muscle may incline the body laterally ; and contracting with of one. 

 the opposite external oblique (the fibres of the two having the same 

 direction), it will rotate the trunk to the same side. 



The CREMASTER MUSCLE (fig. 100, D) is a muscular slip which lies Cremaster 

 along the lower border of the internal oblique, and is named from its m 

 suspending the testicle. The muscle is attached both at the inner and 



