Dorsal interossei muscles
The dorsal interossei muscles of the hand, as their name suggests, are found on the dorsum or posterior aspect of the hand between the metacarpal bones. Each hand possesses four dorsal interossei muscles and each of these short muscles has a unique origin and insertion point.
The dorsal interossei muscles are found between the first to fifth metacarpals. Each muscle has two heads and therefore two attachment points at its origin. That is to say, each dorsal interossei arises by two heads from adjacent sides of the first to fifth metacarpals. So, for example, the dorsal interossei muscle found between the thumb and the index finger has one head that has its origin on the medial aspect of the metacarpal of the thumb and another head that has its origin on the lateral aspect of the metacarpal of the index finger.
Although these muscles arise by two heads, each one inserts via a single tendon at the dorsal aponeurosis and the base of the proximal phalanx of the digits 2 to 4. Each muscle has its insertion, towards or in the direction of the middle finger as follows; the first dorsal interossei muscle, which is the largest and strongest of the four muscles, inserts on the radial side of the index finger. The second dorsal interossei muscle inserts on the radial side of the middle finger. The third dorsal interosseous muscle inserts on the ulnar side of the middle finger and the fourth dorsal interossei muscle inserts on the ulnar side of the ring finger.
The interossei muscles are innervated by the deep branch of the ulnar nerve (C 8, T 1). The functions of these muscles include, flexion of the metacarpophalangeal joints of the second to fourth digits, extension and abduction of the proximal and distal interphalangeal joints, radial abduction of the middle and index fingers by the first and second dorsal interosseous and ulnar abduction of the middle and ring finger by the third and fourth dorsal interossei.
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