434 THE MUSCLES AND 



being placed immediately beneath the Internal oblique. It arises by fleshy fibres 

 from the outer third of Poupart's ligament; from the inner lip of the crest of the 

 ilium for its anterior three-fourths; from the inner surface of the cartilages of the 

 six lower ribs, interdigitating with the Diaphragm; and from the lumbar fascia 

 (Fig. 327), which may be regarded as the posterior aponeurosis of the muscle. 

 The muscle terminates in front in a broad aponeurosis. the lower fibres of which 

 curve downward and inward, and are inserted, together with those of the Internal 

 oblique, on the crest of the os pubis and iliopectineal line, thus forming what is 

 known as the conjoined tendon of the Internal oblique and Transversalis muscles. 

 Throughout the r of its extent the aponeurosis passes horizontally inward, 

 and is inserted into the linea alba, its upper three-fourths ^passing behind the 

 Rectus abdominis muscle, blending with the posterior lamella of the Internal 

 oblique: its lower fourth passing in front of the Rectu.s. 



The conjoined tendon of the Internal oblique and Transversalis is chiefly formed 

 by the lower part of the tendon of the Transversalis, and is inserted into the crest 

 of the os pubis and iliopectineal Jine. immediately behind the external abdominal 

 ring, thus serving to protect what would otherwise be a weak point in the abdominal 

 wall. The conjoined tendon is sometimes divided into an outer and an inner 

 portion the former termed the ligament of Hesselbach, the latter, the ligament 

 of Henle (Fig. 322). 



Relations. By its siiperficial surface, with the Internal oblique, the lower intercostal nerves, 

 and the inner surface of the cartilages of the lower ribs; by its deep surface, with the fascia 

 transversalis, which separates it from the peritoneum. Its lower border forms the upper 

 boundary of the inguinal canal. 



Dissection. To expose the Rectus abdominis muscle, open its sheath by a vertical incision 

 extending from the costal arch to the os pubis, and then reflect the two portions from the 

 surface of the muscle, which is easily done, excepting at the lineae transversae, where so 

 close an adhesion exists that the greatest care is requisite in separating them. Now raise the 

 outer edge of the muscle, in order to examine the posterior layer of the sheath. By dividing 

 the muscle in the centre, and turning its lower part downward, the point where the posterior 

 wall of the sheath terminates in a thin curved margin will be seen. 



The Rectus abdominis (m. rectus abdominis} (Figs. 325 and 326) is a long flat 

 muscle, which extends along the whole length of the front of the abdomen, being 

 separated from its fellow of the opposite side by the linea alba. It is much broader, 

 but thinner, above than below, and arises by two tendons; the external or larger is 

 attached to the crest of the os pubis. the internal, smaller portion interlaces with 

 its fellow of the opposite side, and is connected with the ligaments covering the 

 front of the symphysis pubis. The fibres ascend, and the muscle is inserted by 

 three portions of unequal size into the cartilages of the fifth, sixth, and seventh 

 ribs. The longest portion attached principally to the cartilage of the fifth rib, 

 usually has some fibres of insertion into the anterior extremity of the rib itself. 

 Some fibres are occasionally connected with the costoxiphoid ligaments and side 

 of the ensiform cartilage. 



The Rectus muscle is traversed by tendinous intersections, three in number, 

 which have received the name of lineae transversae (inscriptiones tendineae}. One 

 of these is usually situated opposite the umbilicus, and two above that point; of 

 the latter, one corresponds to the extremity of the ensiform cartilage, and the other 

 to the interval between the ensiform cartilage and the umbilicus. These inter- 

 sections pass transversely or obliquely across the muscle in a zigzag course; they 

 rarely extend completely through its substance, sometimes they pass only half- 

 way across it, and are intimately adherent in front to the sheath in which the 

 muscle is enclosed. Sometimes one or two additional lines may be seen, one 

 usually below the umbilicus; the position of the other, when it exists, is variable. 

 These additional lines are for the most part incomplete. 



