Anatomy of intrinsic hand muscles

The intrinsic hand muscles consist of the thenar, hypothenar and midcarpal muscles. Our recent studies on these muscles and their innervation have revealed several new findings which would enhance standard anatomical descriptions of these muscles. 1) R. profundus of the ulnar nerve sends off branches to interossei in order of the spatial arrangement of these muscles. 2) Regarding the thenar muscles, M. opponens pollicis, M. flexor pollicis brevis and M. adductor pollicis form a single mass without clear borders, and their supplying nerves originate from the thenar ansa which is established by anastomosis of one or two branches of the median nerve and a terminal branch of R. profundus of the ulnar nerve. We call this muscle mass the "deep thenar muscle." Due to the lack of definite margins, it is understandable that the anatomical descriptions of the thenar muscles have been so varied. The division of the deep thenar muscle into the three muscles might be regarded as only an artificial division, according to arbitrary criteria.