Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: T
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
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:
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).
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.
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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