Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: I

Interossei (Manus)

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The palmar interossei insert into the extensor expansion. The first dorsal interosseous muscle inserts into the extensor expansion. The first dorsal interosseous muscle usually inserts into the the proximal phalanx. The three other dorsal interossei are variable. Most frequently they insert into the extensor expansion and the proximal phalanx. The second dorsal interosseus inserts into the proximal phalanx more frequently than the fourth, and the fourth more frequently than the third. In about 3% of cases the first dorsal interosseus is innervated by the median nerve.

The second dorsal interosseus may have three heads.

Macalister reported the variations of the interossei as follows:

1. The first dorsal has been found divided into two, one part going to the pollex and one to the index; this is a very rare anomaly, not occurring more often than once in 120 subjects;
2. This muscle receives occasionally a slip from the extensor carpi radialis longus;
3. The third dorsal has received a slip from the extensor carpi radialis brevis;
4. Macalister found all the dorsals divided in one case;
5. The dorsals of the second or third interspaces sending a slip or slips to extensor digitorum brevis manus;
6. A first palmar interosseus, or interosseus primus volaris of Henle is relatively common; Mr. Wood (1867) found it three times in thirty-six subjects; Macalister found the same muscle in the same proportion; it sometimes receives a slip from extensor carpi radialis longus, or accessorius;
7. Macalister found a doubled set of palmar interossei twice;
8. Two in the second intermetacarpal space;
9. A doubled third palmar;
10. The second dorsal attached to the ulnar side of the index, and the first palmar to the radial side of the middle finger; this is the arrangement ordinarily found in the foot, and an instance of its being found as a hand arrangement was described by Meckel;
11. Two palmars in the fourth metacarpal interspace, one to the little, and the other to the ring finger;
12. Two in the third interspace for the ring and middle fingers;
13. Two in the second for the index and middle;
14. The indicial part of the first dorsal was found absent by Macalister;
15. The second dorsal inserted into the ulnar side of the index;
16. And the first palmar to the radial side of the middle finger.

Unusual Dorsal Interosseous Muscle.
id III, third dorsal interosseous muscle; id II, second dorsal interosseous muscle; and idx , irregular third head of the second dorsal interosseous muscle. from Brunn.

References

Baumann, J.A. (1947) Valeur, variation, et équivalences des muscles extenseurs, interosseux, adducteurs et abducteurs de la main et du pied chez l'homme. Acta Anat. 4:10-16.

Brunn, A. von. (1873) Varietät des Musc. interosseus dorsal manus II. Arch. Anat. Physiol. Wissen. Med. 1873:126.

Jacquart, H. Exemple d'insertion anormale du muscle adducteur du pouce sur une main d'homme, qui prouve que ce muscle n'est en réalite que le premier interosseux palmaire. Soc. Biol., Comptes Rendus des Séances et Mémoires.

Kuczynski, K. The variations in the insertion of the first dorsal interosseous muscle and their significance in the rheumatoid arthritis. Hand. 4:37-39.

Lamont, J.C. (1908) Note on a tendon found in association with the insertion of the peroneus longus, and the origin of the first dorsal interosseus muscle. J. Anat. Physiol. 42:236.

Panas, -. (1863) Muscles interosseaux dorsaux surnuméraires de la main. Bulletins et Mem. de la Société Anatomique de Paris. XXXVIII(4):165.

Macalister, A. (1875) Observations on muscular anomalies in the human anatomy. Third series with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-130.

Salisbury, C.R. (1936-37) The interosseus muscles of the hand. J. Anat. 71:395-403.

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