THE DEVELOPMENTAL ANATOMY OF THE EXTENSOR ASSEMBLY

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Abstract
Serial, horizontal, polychromatically stained sections of the hand of 2 human embryos and 5 fetuses were examined. The major elements of the extensor expansion were differentiated by 45 mm C.R. In the fetuses studied here an interosseous attachment to the side of the fibrous flexor sheaths was almost constant. Considerable variation in the details of attachment of an individual interosseous or lumbrical muscle was noted, resulting presumably in corresponding variation of individual action components. Superficial and deep bellies were not apparent at these developmental phases. An attachment between the collateral extensor tendon and the fibrous flexor sheath was observed and has been identified tentatively as the "transverse retinacular band". A distinct "oblique retinacular band or link ligament was not noticed in the present series. In contrast to authors who, on the basis of dissection, claim only a bony insertion for the 1st dorsal interosseus, this muscle was found, in the present investigation, to be inserted into both expansion and capsule. The expansion component of the abductor pollicis brevis was inserted into the extensor pollicis brevis rather than into the extensor pollicis longus.

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