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

Extensor Digitorum Brevis (Pedis)

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The tendons vary in number. They may be reduced to two or even one, and cases have been described in which the muscle was absent. In very rare instances, a slip may join the long extensor tendon of the little toe, increasing the slips to five. When five tendons are present, it is usually due to the presence of supernumerary fascicles arising between the normal slips and ending in various ways. Such slips are not infrequent, especially in the interval between the great (big) and second toes. One of these slips may join an interosseous muscle.This muscle varies greatly in development; rarely the entire muscle may be absent or, more frequently one or more of its digital divisions. It may also be developed to a greater degree than usual.

Accessory fasciculi vary markedly in their origin and termination. Most frequently, the tendons insert somewhere on a metacarpophalangeal articulation or end somewhere on the second or fifth toes. An accessory slip from extensor hallucis longus may, through a tendon several cm. in length, join a slip to the big toe (usually m. extensor hallucis brevis).

Extensor brevis digitorum pedis has been reported by Macalister as follows:

1. It may be reduced to the first and fourth toe muscles;

2. Or to the second and third alone;

3. A slip from the second tendon joined the first dorsal interosseous, and from the third tendon to the second dorsal interosseous;

4. A doubled tendon for the second toe;

5. A slip from the second tendon of the longus to this muscle (McWhinnie);

6. Two separate slips to the second toe;

7. A separate slip to the little toe;

8. A slip to the fourth toe muscle from extensor longus;

9. A separate extensor hallucis brevis; this is a more common arrangement than the union of this with the other parts of extensor brevis, and is regarded by Henle as the normal condition;

10. A bicipital second toe extensor, the second head arising from the ectocuneiform (outside or lateral cuneiform) and the base of the third metatarsal (Lotze);

11. Doubled heads for the second and third toe extensors;

12. Reduced to a little and third toe muscle.

Macalister also commented on interossei pedis as follows:

1. The fourth plantar arose from a slip of peroneus longus;

2. The first plantar has been found bipenniform and perforated by an artery;

3. The first and fourth dorsal with only single heads;

4. An interosseus plantaris hallucis, homologous with that of Henle in the hand, has been found.

Syn.: m. extensor digitorum communis brevis (Meckel) and (Henle), extensor digitorum pedis brevis, pediaeus externus pedieux (Cruveilhier).

References

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

Henle, J. (1871) Handbuch der Muskellehre des Menschen, in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.

Macalister, A. (1875) Additional observation on muscular anomalies in human anatomy (third series), with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-134.

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