Encyclopedia entry

Extensor Pollicis Brevis

Version 1

Abstract

Extensor pollicis brevis, a muscle peculiar to (or individualized to a greater degree in) humans is sometimes absent, being fused with abductor longus, as in the Simiidae. On the other hand, its tendon is often united with that of the long extensor and is inserted with it, or it may be continued as an independent slip to the base of the distal phalanx. In a study of 118 forearms extensor pollicis brevis inserted onto the first phalanx in 72% of cases, both phalanges in 21%, and the terminal phalanx only, in 6.8%. Extensor pollicis brevis has been reported absent in 6.3% of cases.

Extensor pollicis brevis, a muscle peculiar to (or individualized to a greater degree in) humans is sometimes absent, being fused with abductor longus, as in the Simiidae. On the other hand, its tendon is often united with that of the long extensor and is inserted with it, or it may be continued as an independent slip to the base of the distal phalanx.

In a study of 118 forearms extensor pollicis brevis inserted onto the first phalanx in 72% of cases, both phalanges in 21%, and the terminal phalanx only, in 6.8%. Extensor pollicis brevis has been reported absent in 6.3% of cases. In another study, the muscle was absent in five of 120 limbs. The muscle may terminate in two tendons, one of which attaches to the base of the first metacarpal.

Macalister has reported the following variations for extensor pollicis brevis: 1. It has been found absent by Wood (1867 and 1868) once in 36 specimens and three times in 36 specimens, this has also been found by S. Moser, and by Macalister; 2. Theile and Henle have seen it fused with abductor pollicis longus as have Wood and Macalister; 3. Its tendon may pass distally to the ungual distal phalanx; 4. The tendon has been described as split (B), and Macalister has found the entire muscle cleft with each part normally attached; 5. Mr. Wood found it replaced by a tendon from the styloid process of the radius to its normal site of insertion; 6. A slip to the tendon of the extensor secundi (extensor pollicis longus) at the base of the ungual phalanx (S); 7. The tendon entirely going to the ungual phalanx; 8. A slip has been seen going to the metacarpal bone at its head; and 9. Or it has been found receiving a slip from the abductor which passed it on to the second phalanx.

Syn.: m. Extensor primi minor, extensor primi internodii pollicis.

Riferimenti dell’opera originale

Elenco riportato come compare nella fonte, senza normalizzazione dei formati bibliografici.

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Anatomical classification

Systems:
Muscular system

Content provenance

Adaptation

Adaptation of «Extensor Pollicis Brevis — Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System» by Ronald A. Bergman, Adel K. Afifi, Ryosuke Miyauchi. Source: https://www.anatomyatlases.org/AnatomicVariants/MuscularSystem/Text/E/26Extensor.shtml Original work distributed under the CC BY-NC-SA 4.0 licence (https://creativecommons.org/licenses/by-nc-sa/4.0/deed.it). Adaptation by Redazione AIVA. Changes from the original: Testo originale inglese riprodotto integralmente e riorganizzato nel formato scheda del portale (sintesi, testo, riferimenti), senza modificarne le affermazioni. La traduzione italiana non è ancora stata eseguita, e la pagina lo dichiara. Le figure non sono state copiate: sono collegate alla pagina d’origine. This publication is not approved or endorsed by the authors of the original work.

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