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Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: O

Obliquus Externus (External Abdominal Oblique)

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed


The external oblique varies in the number of its attachments to the ribs. Absence of the highest and lowest digitation is common. On the other hand, one or more slips may be doubled, most frequently those from the eight or ninth ribs, or an additional slip may arise from the lumbar fascia below the last rib.

In addition to the connection with the pectoralis major, there may be union, frequently by tendinous intersection or more rarely by direct continuity, between the slips of origin of the external oblique and serratus anterior muscles. A similar connection may exist between external oblique and latissimus dorsi or serratus posterior inferior. In some cases, deep accessory bundles arise from the ribs and are separated by connective tissue from the main sheet of muscle. These slips arise from one or more of the lower ribs and are attached independently at their distal end to the iliac crest, anterior superior iliac spine, inguinal ligament, or sheath of the rectus.

Detached slips may arise beneath the digitations from the fourth to the seventh ribs and from the fascia over the fifth/sixth intercostal space, and end in the upper part of the rectus sheath. A rather bizzare detached slip, named the saphenous muscle, has been described. It is attached at both ends to the inguinal ligament and loops around the saphenous vein.

The presence of a tendinous intersection in the external oblique muscle is interesting in view of its segmental character, as evidenced by the regularly arranged tendinous intersections in the muscle found in many mammals.

Cases of congenital deficiency of the abdominal muscles have been reported. These cases are ultimately fatal (and therefore outside the scope of this compilation).

Syn.: m. Obliquus abdominis externus, s. descendens, s. oblique descendens. Aeusserer schiefer Bauchmuskel. Grand oblique.

Image 65

Congenital absence of abdominal muscles (Prune Belly) from Guthrie, 1896


References

Anson, B.J., Ed. (1966) Morris' Human Anatomy. 12th ed. The Blakiston Division, McGraw-Hill Book Company, New York.

Budge, J. (1859) Beschreibung eines neuen Muskels und mehrerer Miskel- und Knochenvarietäten Zeitschrift für Rat. Med. 3:273-278.

Gruber, W. (1875) Zwei neue Fälle eines rudimentären Musculus obliquus externus abdominis II. Arch. Path. Anat. Physiol. Klin. Med. 65:18-21.

Gruber, W. (1887) Ein rudimentärer Musculus obliquus abdominis externus accessorius. Arch. Path. Anat. Physiol. Klin. Med. 110:561.

Guthrie, L. (1896) Case of congenital defiency of the abdominal muscles, with dilation and hypertrophy of the bladder and uterus. Trans. Path. Soc. London. 47:139-145.

Henle, J. (1873) Sinnesapparte, in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.

Macalister, A. (1875) Observations on muscular anomalies in the human anatomy. Third series with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-130.

Miyauchi, R. (1986) On the human obliquus abdominis externus profundus. Acta Medica Nagasakiensia. 31:59-75.

Mori, M. (1964) Statistics on the musculature of the Japanese. Okajimas Fol. Anat. Jap. 40:195-300.

Nakayama, T. and S. Okuda (1952) On the M. obliquus abdominis externus profundus. Kaibogaku Zasshi. 27:89-94. In Japanese.

Nussbaum, N. (1893) Vergleichend anatomische Beiträge zur Kenntnis der Augenmuskeln. Anat. Anz. 8:208-210.

Sugiura, R. (1935) On a superfluous muscle accompanying the M. obliquus externus abdominis sinister. Nagoya Journal of medical sciences. 8:139-143. In Japanese. Tyrie, C.C.B. (1894) Musculus saphenous. J. Anat. Physiol. 28:288-290.

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