Each palmar interosseous muscle arises from the entire length of the metacarpal bone of one finger, and is inserted into the side of the base of the proximal phalanx and extensor expansion of the extensor digitorum tendon to the same finger.
There are three palmar interossei:
| # | Origin | Insertion |
| first | from the ulnar side of the second metacarpal bone | into the same side of the proximal phalanx of the index finger |
| second | from the radial side of the fourth metacarpal bone | into the same side of the ring finger |
| third | from the radial side of the fifth metacarpal bone | into the same side of the little finger |
The palmar interossei are unipennate.
From this account it may be seen that each finger is provided with two interossei, with the exception of the little finger, in which the abductor digiti minimi muscle takes the place of one of the pair.
Some texts consider the medial head of the flexor pollicis brevis to be a palmar interosseous muscle. This muscle would then be considered the first palmar interosseous muscle, and the total number of palmar interosseous muscles in the hand would be four.
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