Adductor Pollicis
Adductor pollicis is a triangular muscle that shows a tendency to split into radial parts. The relative extent of the division and the closeness of their connection is variable. Occasionally, fasiculi are seen arising from the palmar metacarpophalangeal ligaments, forming a transversus manus (Hallett).
Mori describes the variations of this muscle as follows:
Origin:
The transverse head arises from the third and fourth metacarpal bones in 76 %.
The transverse head arises from the third metacarpal bone only in 24%.
The Belly of the Muscle.
Two heads are completely separated in 82%.
Two heads are incompletey separated in16%.
The transverse head is divided into two layers in 2%.
A contrahentes digitorum has been reported, which is usually present in amphibia and most mammals but usually absent in the gorilla, orangutan, and humans. When present in humans, it arises from the carpals or the base of the metacarpals and inserts on the head of the fourth and fifth metacarpals and phalanges. It adducts the fourth and fifth digits toward the midaxial line (third or middle digit). Its embryological development has been described. Although the muscle typically disappears as such, a part may persist and is incorporated into the adductor pollicis.
Syn.: mesothenar (Winslow).
References
Baumann, J.A. (1947) Valeur, variation, et équivalences des muscles extenseurs, interosseux, adducteurs et abducteurs de la main et du pied chez l'homme. Acta Anat. 4:10-16.
Chudzinski, - Sur une anomalie du muscle adducteur du pouce, observe é chez la negresse Louise Zoulou. Bull. Soc. Anthropol. Paris. 4:748-751.
Henle, J. (1871) Handbuch der Muskellehre des Menschen, in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.
Hepburn, D. (1893) The adductor muscles of the thumb and great toe. J. Anat. Physiol. 27:282-284.
Jacquart, H. (1859) Example d'insertion anormale du muscle adducteur du pouce sur une main d'homme, qui prouve que ce muscle n'est en réalité que le premier interosseux palmaire. Soc. Biol., Comptes Rendus des Séances et Mémoires. 11:252-253.
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.
Stark, H.H., Otter, T.A., Boyes, J.H., and T.H.Richard. (1979) "Atavistic contrahentes digitorum" and associated muscle abnormalities of the hand: A cause of symptoms. J. Bone Joint Surg. 61A:286-289.