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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: T: Transversus Abdominis

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

Transversus Abdominis

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

Peer Review Status: Internally Peer Reviewed

The number of costal slips varies: it may be reduced to five or increased to seven. The muscle has been fused with internal oblique; it has also been reported absent. Absence of the inguinal bundles has been reported; on the other hand, extension of the transversus to the pubic crest has also been noted, and the spermatic cord has been seen piercing its lower border. The insertion onto the seventh rib may be absent, but in some cases there may be a supernumerary digitation for the sixth rib. The muscle bundles may extend as far as the spermatic cord, they may remain superior to the anterior spine of the ilium, or may have an intermediate position. Beneath the transversus, supernumerary muscle slips, e.g., tensor laminae posterioris vaginae musculi recti, have been reported.

Based on a study of 200 body-halves, it has been reported that, while the internal oblique arises from almost the entire inguinal ligament, the transversus abdominis seldom (3%of cases) arises from the entire inguinal ligament. The inferior edge of transversus seldom forms an arch but it is not the roof of the inguinal canal.

The internal oblique and transversus unite to form a conjoined aponeurosis rather than a conjoined tendon. The conjoined tendon has been defined by Cunningham, as the union of internal oblique and transversus abdominis muscles, which arise from the inguinal ligament and insert medially into the linea alba and inferiorly onto the pubic crest and the pectineal line. The term conjoined tendon is a misnomer in most cases (about 95%). Only when the fused aponeuroses of the two muscles are unusually thickened (5% of cases), the fibers curve downward in front of the spermatic cord and insert onto the iliopectioneal line.

A curious muscle, transversus colli, described by Luschka as a cranial extension of transversus abdominis (and thoracis), arises from the upper edge of the first costal cartilage, courses between sternohyoideus and sternothyroideus, and inserts into the interclavicular ligament or capsule of the sternoclavicular joint and surrounding fascia.


Chandler, S.B. and M. Schadewald. (1942) The conjoined aponeurosis versus the conjoined tendon. Anat. Rec. 82:404.

Chandler, S.B. and M. Schadewald. (1944) Studies on the inguinal region. I. The conjoined aponeurosis versus the conjoined tendon. Anat. Rec. 89:339-343.

Gruber, W. (1873) Sur quelques muscles surnumeraires de l'abdomen chez l'homme. Bull. l'Acad. Imp. Sci. St. Petersbourg. 18:142-147.

Gruber, W. (1880) Ein mit seiner inguinalen Portion durch die ganze Regio inguinalis sich herab erstreckender Musculus transversus abdominis. Arch. Path. Anat. Physiol. Klin. Med. 80:88-91.

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.

Schaefer, E.A., Symington, J. and T.H. Bryce., Eds. (1923) Quain's Elements of Anatomy,11th ed., Longmans, Green and Co., London.

Testut, L. (1884) Les Anomalies Musculaires Chez l'Homme Expliques par l'Anatomie Comparée., Masson, Paris.

Zieman, S.A. (1940) The fallacy of the conjoined tendon. Am. J. Surg. 50:17-21.

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