Fig 1.
Schematic drawings of the right hand, palmar view, with the thenar muscles shown in two layers.
Only bony attachments are shown. Left) Overview of the thenar muscles as visible after skinning the hand. Both heads of the flexor pollicis brevis are covered by the abductor pollicis. Right) Abductor pollicis and opponens pollicis are completely removed. The deep head of Cruveilhier (orange; a.k.a. the deep head of the flexor pollicis brevis) is shown with two heads attaching onto the ulnar and radial side at the base of the proximal phalanx of the thumb. The superficial head of the flexor pollicis brevis (dark orange) has a single head that inserts ulnarward onto the proximal phalanx of the thumb.
Fig 2.
Schematic drawings of three possible configurations for the deep head of Cruveilhier.
A) Overview of muscles attaching onto the proximal phalanx of the thumb. The deep head of Cruveilhier has two heads that insert radialward and ulnarward onto the base of the proximal phalanx 1. B) The deep head of Cruveilhier with only ulnar insertion. In some specimens, like the one depicted here, the most radialward fibers of the oblique head of the adductor pollicis form another slip that can be mistaken for the deep head of Cruveilhier. However, the origin is continuous with the fibers of the rest of the oblique adductor pollicis. C) The deep head of Cruveilhier with only radial insertion. Drawings by Marie Dauenheimer.
Fig 3.
Palmar view of left hand (#754) with split deep head of Cruveilhier.
Split head of Cruveilhier inserting onto the ulnar and radial sesamoid at the proximal phalanx of the thumb. A) Abductor pollicis reflected to show the opponens pollicis. B) Tendon of the flexor pollicis longus reflected and superficial head of the flexor pollicis brevis retracted for better view of the origin and insertion of the deep head of Cruveilhier. Blue scale = 1 cm.
Fig 4.
Innervation of the deep head of Cruveilhier.
Palmar view of right hands. A) The dissection of the radial and median nerve (#766R). After dissection the schematic drawing on the right were done for all hands. B) The median nerve mostly innervates the radial head of the deep head of Cruveilhier. In cases where the median nerve is also innervating the ulnar head the branch usually passes under the tendon of the flexor pollicis longus. The exception is shown here (#779R). Blue scale = 1 cm.
Fig 5.
Palmar view of dissected ulnar and median nerve in hands indicated in A-E. Variability of branching pattern in both nerves is obvious. All hands have a split deep head of Cruveilhier with insertions onto the ulnar and radial proximal phalanx. The ulnar slip is always innervated by the ulnar nerve and the radial slip by the median nerve, except for C (#774R) where the ulnar head receives innervation from both nerves. The recurrent nerve (Rec) of the median nerve innervates the flexor pollicis brevis (FPB), the abductor pollicis brevis (Ab), and the opponens pollicis (Op). The deep palmar ulnar nerve innervates the palmar and dorsal interossei (I) while crossing the palm from medial to lateral (towards the thumb). In the thenar compartment it branches and innervates the adductor pollicis transverse (At) and oblique (Ao) heads, the muscle of Henle (H), and the first dorsal interossei (the terminal I). The innervation of the ulnar (U) and radial (R) heads of the deep head of Cruveilhier is indicated in Red to for better visualization. The palmaris brevis (Pb) is innervated by the superficial branch of the ulnar nerve and the hypothenar muscles, opponens digiti minimi (Om), flexor digiti minimi (Fm), and abductor digiti minimi (Am) are innervated by the deep ulnar nerve. One exception to this pattern is shown in Fig 5A.
Table 1.
Day and Napier’s [34, 35] study of the deep head of Cruveilhier compared to the results of the present study.
Table 2.
Innervation of the heads of the flexor pollicis brevis.