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

Extensor Carpi Radialis Brevis and Extensor Carpi Radialis Longus

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

A trigastric radialis longus has been reported inserting partially onto the base of the first metacarpal and partially onto the base of the second metacarpal. Incomplete fusion frequently occurs, effected by cross slips from one muscle to the other. The longus and brevis are noted for exchange of fleshy and tendinous slips. These connecting slips may be replaced by distinct muscles connected with one or both radial extensors.

Extensor carpi radialis intermedius is a rare muscle that arises independently from the epicondyle of the humerus between the two usual muscles and is inserted into the second and third metacarpals. More frequently, the accessory muscle is represented by a slip from one or both of the radial extensors and is inserted, in the same way, onto the second or third metacarpal or onto both of these bones. Extensor carpi radialis accessorius is an additional muscle sometimes seen arising from the humerus, with or below the long radial extensor, and inserting most frequently onto the metacarpal bone of the thumb. It is represented at times by a slip from the tendon of extensor longus. The muscle of the two extensors are usually separated, but, more commonly, it is one of the tendons that is split into two or sometimes three tendons prior to insertion. The tendons may be attached to the second and third metacarpal bones. Occasionally, a slip also passes to the fourth metacarpal or to the trapezium.

Extensor carpi radialis longus may be joined to abductor pollicis longus or to some of the dorsal interosseous muscles.

Syn.: Radialis extensor brevis s. secundus, Kurzer ausserer Speichenmuskel, Kurzer Speichenstrecker, Second radial externe (Cruveilhier).

Radialis extensor longus, Langer ausserer Speichenmuskel, Langer Speichenstrecker, Premier radial externe (Cruveilhier).

Duplication of Extensor Carpi Radialis Brevis and division of its tendon (C), and Pisipalmaris (A,B).
Absence of Palmaris Longus.
Note that its the accessory muscle that inserts onto the bases of the first and second metacarpal bones.
from Calori.

References

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Calori, L. (1868) Delle anomalie più importanti di ossa, vasi, nervi e muscoli occorse nell'ultimo biennio facendo anatomia del corpo umano. Mem. R. Accad. Sci. Istituto di Bologna S.2. 8:417-482.

Curnow, J. (1873) Notes of some irregularities in muscles and nerves. J. Anat. Physiol. 7:304-309.

Gruber, W. (1877) Über den Muskulus radialis externus accessorius. Arch. Anat. Physiol. Wissen. Med. 1877:388-389.

Gruber, W. (1885) Über die im Bereiche des Lig. carpi dorsale schon congenital und in der Norm vorkommende Communication der Sehnenscheide fur den Extensor pollicis longus mit der fur die Radialis externi (nach 500 Untersuchungen), und uber einen Fall von Hygroma proliferum dieser mit einander communicirender Sehenenscheiden. Arch. Path. Anat. Physiol. Klin. Med. 101:245-253.

Kaneff, A. (1969) Sehr seltene Kombination von Muskelvärietäten der radialen und dorsalen Muskelgruppen eines menschlichen Vorderarmes. Anat. Anz. 125:535-538.

Macalister, A. (1875) Additional observations 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.

Matsushima, R. and T. Ikuta. (1959) An anomalous case of extensor carpi radialis brevis and longus. Studies Depart. Anatomy, Hiroshima Univ. School Med. 4:17-19. In Japanese.

Shepherd, F.J. (1880) Notes of abnormalities observed in the dissecting-room of McGill University from October 1875, to May, 1879. Ann. Report. Montreal General Hospital 1:71-93.

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Wood, J. (1866) Variations in human myology observed during the winter session of 1865-66 at King's College, London. Proc. Roy. Soc. Lond. B 15:229-244.

Wood, J. (1867) Variations in human myology observed during the winter session of 1866-67 at King's College, London. Proc. Roy Soc. Lond. B 15:518-546.

Wood, J. (1867) On human muscular variations in their relation to comparative anatomy. J. Anat. Physiol. 1:44-59.

Wood, J. (1868) Variations in human myology observed during the winter session of 1867-68 at King's College, London. Proc. Roy. Soc. Lond. B 17:483-525.

Wood, V.E. (1988) The extensor carpi radialis intermedius tendon. J. Hand Surg. (A) 13:242-245.

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