Triceps Brachii

Variations in the triceps are neither numerous or common. Each of the heads may be fused, in varying degrees, with neighboring muscles.

The fibers of the long head may be found extending to the capsule of the shoulder joint above or distally, for a greater extent than usual on the axillary border of the scapula.

Macalister (1875) described the variations of triceps extensor cubiti (triceps brachii) as follows:

  1. It may have a fourth head from the medial part of the humerus below the head, by a long, slender tendon, and by an aponeurotic expansion from the capsule of the shoulder- this head blended with the inner (medial ) head (Blumenthal);
  2. Macalister has frequently seen the long head split, one attached to the capsule, and the other to the tricipital spine, axillary border, or the first slip was found splitting the capsular ligament, like the curved head of rectus femoris;
  3. The existence of a slip from the tendon of latissimus dorsi has been seen several times. It was described by Bergman (1855) ; and it was also mentioned by Halbertsma under the name of anconeus quintus; this may occasionally come from the teres major.
  4. This slip is the remains of the tricipiti accessorius, or the dorsiepitrochlearis, which is present, in some form or other, in all quadrumana (four-footed animals).

Macalister reports:

  1. A tendon of union for the lower border of latissimus dorsi to the long head;
  2. A fleshy slip of connection from the costal fibers of latissimus dorsi into the same part of triceps;
  3. Harrison describes the triceps as attached occasionally to the anconeus; this Macalister has also seen;
  4. A slip from the long head up to the coracoid process, an additional head, was found by Gruber;
  5. A slip from subscapularis;
  6. A small slip connected to the capsule of the shoulder has been seen continued up to the upper portion of the glenoid cavity;
  7. A doubled fourth head, one from the coracoid process, and one from the capsule of the shoulder: all of these cases Macalister has actually verified;
  8. Fusion of the external head with the origin of the extensor carpi ulnaris, is described by Jenty; A second lateral head is described by Meckel (1826). Theile has written a shot monograph on this muscle in Müller's Archives. 1839.
  9. A slip from the long head, anconeus quintus, which is present in 5% of bodies, may join latissimus dorsi. It then corresponds to latissimocondyloideus (dorsoepitrochlearis or accessorium tricipitis), which is common among the anthropoid apes. An accessory or fourth head has been reported arising from the medial aspect of the humerus above or near the deep head, and inserting at the axillary border of the scapula, the tendon of latissimus dorsi, from the coracoid process, or even the capsule of the shoulder joint. Occasionally the medial head of the triceps extends distally to form an arch across the ulnar groove. The tendon of insertion of triceps brachii may contain a sesamoid bone, the patella cubiti (sesamum cubiti or "elbow disk").

Epitrochleo-olecranonis (epitrochleoanconeus, epitrochleocubital, or anconeus sextus [Gruber]), a muscle distinct from triceps, extends from the medial epicondyle of the humerus and arches across the groove for the ulnar nerve to insert on the olecranon process. It occurs in about 25% (or less) of bodies, and takes the place of the fibrous arch normally passing between the epicondylar and ulnar heads of flexor carpi ulnaris. Mori found this muscle in 5% of 96 arms. Triceps brachii and epitrochleo-olecranonis may be fused with anconeus.

Syn.: m. extensor cubiti, brachialis s. brachieus externus s. posticus (Meckel), Dreiköpfiger, Vorderarmstrecker. Long head; anconeus longus, caput longum s. primum. Lateral head; anconeus brevis, caput externum s. magnum s. secundum (henle), Vastus externus (Cruvielhier). Deep head; anconeus internus, caput internum s. tertium s. parvum, brachialis externus (Albin), anconeus brevis (theile), vastus internus (Cruveilhier).

Four-Headed Triceps Brachii.

Al, Long head; Ab, lateral head; Ai, medial head; *, tendon of fourth head.
from Blumenthal.

References

Anson, B.J., Ed. (1966) Morris' Human Anatomy, 12th ed. The Blakiston Division, McGraw-Hill book Company, New York.

Blumenthal, C. (1871) M. extensor triceps als quadriceps. Zeitschrift für Rationelle Medicin 36:1-4.

Gruber, W. (1866) Über den Musculus epitrochleo-anconeus des Menschen und der Säugethiere. Mem. de L'Acadèmie Impèriale des Sciences de St. Petersbourg S. 7., 10(5):1-26.

Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series), with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-134.

Mori, M. (1964) Statistics on the musculature of the Japanese. Okajimas Fol. Anat. Jap. 40:195-300.

Williams, P.L., Warwick, R., Dyson, M., and L.H. Bannister., Eds. (1989) Gray's Anatomy, 37th ed., Churchill Livingstone, Edinburgh.

Wood, J. (1867) On human muscular variations in their relation to comparative anatomy. J. Anat. Physiol. 1 :44-59.

Wood, J. (1868) Variations in human myology observed during the winter session of 1867-68 at King's College, London. Proc. Roy. Soc. Lond. B 17:483-525.

 

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