430 THE MUSCULATURE 



inguinal ring [annulus inguinalis subcutaneus]. This opening is formed by the diverging of 

 the lower medial fibres which compose the aponeuroiss of the external oblique muscle. The supe- 

 rior fibres form the upper boundary, superior cms, of the ring and pass to the front of the sym- 

 physis pubis. The inferior fibres form the inferior boundary, inferior cms, of the ring and pass 

 to the pubic tubercle (spine). Between these two fibre bands intercrural (intercolumnar) 

 fibres arch about the lateral boundary of the ring and serve to strengthen the anterior and infe- 

 rior walls of the inguinal canal. Some of the fibres of the superior crus, intermingled with other 

 fibres cross to the opposite side of the body and are inserted into the tubercle (spine) and 

 crest of the pubis and into the superior crus of the opposite side. The structure thus formed 

 is called the reflected inguinal ligament (CoUes's ligament, or triangular fascia). 



Inguinal canal [canalis inguinalis]. — ^This term is apphed to the slit in the lower margin of 

 the abdominal wall through which, in the male, the spermatic cord passes, and in the female, the 

 hgamentum teres. It is not a true canal. The inner end begins at the (internal) abdominal 

 ring [annulus inguinahs abdominahs]. This is situated just above and slightly medial to the 

 middle of the inguinal (Poupart's) ligament. Below the ligament in this region Hes the femoral 

 canal through which the femoral vessels pass into the thigh. The (internal) abdominal ring 

 is covered by the peritoneum and the transversalis fascia. The latter here sends a shallow 

 funnel-like extension outward to be attached to the spermatic cord. The base of this funnel- 

 hke depression toward the inguinal (Poupart's) ligament is formed by a thickened band of 

 tissue, the tractus ilio-pubicus. Medially and laterally the bundles of fibrous tissue which con- 

 stitute this tract spread out fan-like, medially over the sheath of the rectus and toward 

 the pubis, laterally over the transversus muscle and toward the crest of the ilium. The trans- 

 verse abdominal muscle arises from the inguinal ligament nearly as far as the lateral margin of 

 the abdominal ring. The fibre-bundles of this portion of the muscle course ventralward above 

 the base of the funnel mentioned above and are inserted by tendons forming a more or less 

 complete aponeurosis, the "conjoined tendon" [falx inguinalis], common to it and the internal 

 obhque into the ventral sheath of the rectus abdominis muscle, into the tubercle, crest and 

 pecten of the pubis and sometimes into the pectineal fascia or the lacunar (Gimbernat's) 

 hgament. Tendinous bands from the transversalis muscle curve downward medial to the 

 (internal) abdominal ring and help to strengthen the transversalis fascia here. These bands 

 constitute the interfoveolar ligament [ligamentum interfoveolare, Hesselbachi]. The fibrous 

 bands constituting this ligament are attached to the lacunar ligament and the pectineal fascia. 



From the internal ring the spermatic cord (or in the female the ligamentum teres) passes 

 downward and forward in a space (inguinal canal) about 4 cm. long and then through the sub- 

 cutaneous (external abdominal) ring which has been described in connection with the inguinal 

 ligament. The ventral wall of the inguinal canal is composed of the aponeurosis of the external 

 oblique, the intercrural fibres, and the cremaster muscle. Laterally it is also covered by the 

 caudal portions of the internal oblique and transversus muscles. The caudal wall or floor of 

 the space is formed chiefly by the lacunar (Gimbernat's) ligament and laterally also by the ilio- 

 pubic tract. Cranialward the lateral part of the space is covered by the transversus and internal 

 oblique muscles, the medial part by the cremaster muscle. The dorsal (internal) wall is formed 

 mainly by the transversalis fascia. Medially the lacunar (Gimbernat's) ligament and the con- 

 joined tendon (falx inguinalis), when this is well developed, help to form the dorsal wall. 

 Lateral to these structures the dorsal wall is thinner but may be strengthened by a well developed 

 ilio-pubic tract. Near the (internal) abdominal ring it is strengthened by the interfoveolar 

 ligament, and sometimes by muscle slips (interfoveolar muscle). 



Abdominal fossae in the inguinal region. — The hernias so frequent in this region make a 

 special study of the inner surface of the abdominal wall of considerable practical importance. 

 Medial to the abdominal (internal) inguinal ring the inferior internal epigastric vessels give rise 

 to a slight fold {plica epigastrica) which slants medialward and upward toward the rectus muscle. 

 From the lateral margin of the tendon of insertion of the rectus muscle upward toward the 

 umbilicus over the obliterated umbilical artery there extends a better marked fold, the plica 

 umbilicalis lateralis. Lateral to the plica epigastrica lies the fovea inguinalis lateralis, with the 

 internal inguinal ring. Between the plica epigastrica and the phca umbilicalis lateralis lies the 

 fovea inguinalis medialis. In the latter region the fascia transversalis which here forms the 

 inner wall of the inguinal canal is strengthened by two longitudinal fibrous bands belonging to 

 the aponeurosis of the transversalis muscle and described above, the ligament interfoveolare 

 at the medial side of the (internal) abdominal ring, and the falx inguinalis (conjoined tendon) 

 lateral to the rectus muscle. These bands vary in width. When they are narrow the part of 

 the internal wall of the inguinal canal covered merely by the thin transversalis fascia and the 

 peritoneum is relatively large and, since this region lies behind the subcutaneous (external 

 abdominal) ring, opportunity is offered for direct inguinal hernia. 



MUSCLES 



A. Ventral Division 



The rectus abdominis (fig. 388). — Origin — Ventral surface of the fifth to seventh costal 

 cartilages, the xiphoid process, and the costo-xiphoid ligament. 



Insertion. — Tlie upper border of the body of the pubis and the ventral surface of the 

 symphysis. 



Structure.— The muscle is long, flat, and somewhat triangular in form. Cranialward it is 

 broad and thin; caudalward it Ijeconics thicker as it converges toward the insertion. The 

 fibre-bundles of the muscle have a longitudinal course. It is crossed by several incomplete, 

 zigzag, transverse tendinous bands, inscriptiones tendineae, better developed on the ventral 

 than on the dorsal surface of the muscle and intinuitely united to the ventral sheath of the rectus. 

 One of these, corre.sponding segmentally to the tenth rib, is usually situated opposite the um- 



