Transverse Head of the Abductor Pollicis Under the Skin, Anterior View

Description

Presented from the palmar (anterior) aspect beneath the skin of an adult male hand, the highlighted transverse head of adductor pollicis forms a flat, horizontal muscular sheet deep to the thenar fascia. It spans from the anterior surface of the third metacarpal shaft toward the ulnar side of the base of the proximal phalanx of the thumb, blending with the ulnar sesamoid and extensor expansion at the metacarpophalangeal joint. Radial to it lie the thenar muscles (abductor pollicis brevis and flexor pollicis brevis), while proximally and deep sit the oblique head of adductor pollicis and the capitate, and medially the intermetacarpal spaces lead toward the palmar interossei. Bones of the metacarpals and phalanges anchor the scene, with long digital tendons crossing the palm superficial to the deep intrinsic layer. Thumb adduction is easy to describe, harder to visualize without isolating this specific head. The transverse head is the portion most directly tied to power pinch against the index finger, and it sits beside the deep branch of the ulnar nerve as it courses across the palm to supply the interossei and adductor pollicis. Injury at Guyon canal, deep palmar lacerations, or iatrogenic trauma during palmar approaches can denervate this muscle and produce a positive Froment sign, a clinical clue often taught but rarely illustrated with this level of spatial clarity. Small muscle. Big consequence. Use this asset for gross anatomy teaching on intrinsic hand layers, for hand surgery and orthopaedic texts discussing ulnar neuropathy and pinch mechanics, or for rehabilitation materials explaining loss of key pinch after deep ulnar nerve injury. It also fits EMG and peripheral nerve education when correlating motor deficits with the adductor pollicis. Anatomical accuracy verified by SciePro's Medical Advisory Board.