An unusual elbow muscle in the red howler monkey: does it deserve invention of a new name musculus contrahens cubiti?


During dissection of a juvenile specimen of howler monkey (Alouatta seniculus), we discovered a supernumerary muscle. This muscle originates from the lateral epicondyle of the humerus, distal to the m. brahioradialis and beneath the m. extensor carpi radialis longus, and runs deeply to insert on the proximal part of the radius adjacent to the m. supinator.
To determine homology of the unusual muscle, we compared it with the known abnormal extra muscles in the group of preaxial forearm extensors in humans and other primates, as well as other mammals. The only similar muscle is the so-called m. brachioradialis accessorius, which is very rarely found in humans medial to the n. radialis r. superficialis. Both in howlers and humans, its unique topological interrelations with the n. radialis suggest that this muscle is fundamentally different from all surrounding forearm extensors including the proper m. brachioradialis. At the same time, its innervation by the n. radialis confirms that it is a true extensor, contrary to the reptilian m. tractor radii.
The general problem of identifying homology of anomalies and novelties is considered. As the enigmatic muscle departs from rules of myological architecture of the tetrapod forelimb, we failed to establish its general homology and, instead, suggest naming it as m. contrahens cubiti. This means that the muscle acts as the elbow flexor although it intimately belongs to extensors.


general homology problem, anomaly, forearm extensor muscles, brachioradialis, primates, Alouatta


Download data is not yet available.


Alberch, P. 1989. The logic of monsters: evidence for internal constraint in development and evolution. Geobios 22:21–57.

Albright, J. A., and Linburg, R. M. 1978. Common variations of the radial wrist extensors. Journal of Hand Surgery 3:134–138.

Allen, G. M. 1912. Zaglossus. Memoirs of the Museum of Comparative Zoology, Harvard College 40:253–307.

Bergman, R. A., Afifi, A. K, and Miyauchi, R. 2000. Illustrated Encyclopedia of Human Anatomic Variation. Part I: Muscular System.

Cankur, N. Ş., and Özdemir, S. T. 2003. Accessory slip of the extensor carpi radialis longus muscle. Gazi Medical Journal 14:197–199.

Chakravarthi, K. K. 2013. An additional extensor carpi radialis longus muscle and its clinical significance. International Journal of Bioassays 2:887–888.

Claassen, H., and Wree, A. 2002. Multiple variations in the region of mm. extensores carpi radialis longus and brevis. Annals of Anatomy 754:489–91.

Diogo, R., and Abdala, V. 2010. Muscles of Vertebrates: Comparative Anatomy, Evolution, Homologies and Development. Science Publishers, Enfield (New Hampshire).

Diogo, R., and Wood, B. 2012. Comparative Anatomy and Phylogeny of Primate Muscles and Human Evolution. Taylor & Francis, Oxford.

Dunlap, S. S., Thorington, R. W. Jr., and Aziz, M. A. 1985. Forelimb anatomy of New World monkeys: myology and the interpretation of primitive anthropoid models. American Journal of Physical Anthropology 68:499–517.

Gambaryan, P. P., Kuznetsov, A. N., Panyutina, A. A., and Gerasimov, S. V. 2015. Shoulder girdle and forelimb myology of extant Monotremata. Russian Journal of Teriology 14:1–56.

Gruber, W. 1868. Uber die varietaten des musculus brachioradialis. Bulletin de l'Academie Imperiale des Sciences de Saint-Pétersbourg 12:277–287.

Gümüşalan, Y., Kalaycıoğlu, A., Yazar, F., Arifoğlu, Y., and Sinav, A. 1997. Accessory extensor carpi radialis muscle and interconnecting muscular bundle. Acta Anatomica 159:57–60.

Haines, R. W. 1939. A revision of the extensor muscles of the forearm in tetrapods. Journal of Anatomy 73:211–233.

Hill, W. C. O. 1960. Primates Comparative Anatomy and Taxonomy: Cebidae. Edinburgh University Press, London.

Hong, M. K., and Hong, M. K. 2005. An uncommon form of the rare extensor carpi radialis accessorius. Annals of Anatomy 187:89–92.

Jain, A., Kumar, R., Kaur, P., and Angel. 2014. Variations in extensor carpi radialis longus and brevis — a cadaveric study. International Journal of Biomedical Research 5(6):392–395.

Khaledpour, C., and Schindelmeiser, J. 1994. Atypical course of the rare accessory extensor carpi radialis muscle. Journal of Anatomy 184:161–163.

LeDouble, A. F. 1897. Traité des Variations du Système Musculaire de l’Homme et Leur Signification au Point de Vue de l’Anthropologie Zoologique. Schleicher Freres, Paris.

Levit, G. S., Hossfeld, U., and Olsson, L. 2006. From the “modern synthesis” to cybernetics: Ivan Ivanovich Schmalhausen (1884–1963) and his research program for a synthesis of evolutionary and developmental biology. Journal of Experimental Zoology B 306:89–106.

Maclise, J. 1846. On the nomenclature of anatomy (addressed to professors Owen and Grant). Lancet 298–301.

Nayak, S. R., Krishnamurthy, A., Prabhu, L. V., Rai, R., Ranade, A. V., and Madhyastha, S. 2008. Anatomical variation of radial wrist extensor muscles: a study in cadavers. Clinics 63:85–90.

Owen, R. 1846. Report on the archetype and homologies of the vertebrate skeleton. Report of the British Association for the Advancement of Science 169–340.

Owen, R. 1848. On the Archetype and Homologies of the Vertebrate Skeleton. John van Voorst, London.

Owen, R. 1849. On the Nature of Limbs. John van Voorst, London. Pavlinov, I. Ya. 2012. The contemporary concepts of homology in biology: a theoretical review. Biology Bulletin Reviews 2:36–54.

Rao, M. K., Vollala, V. R., Bhat, S. M., Bolla, S, Samuel, V. P., and Pamidi, N. 2006. Four cases of variations in the forearm extensor musculature in a study of hundred limbs and review of literature. Indian Journal of Plastic Surgery 39:141–147.

Richards, R. 2016. Objectivity and the theory of the archetype; pp. 26–37 in Neiman, S., Galison, P., and Doniger, W. (eds.), What Reason Promises: Essays on Reason, Nature and History. De Gruyter, Berlin.

Rodriguez-Nedenführ, M., Vazquez, T., Parkin, I., Nearn, L., and Sañudo, J. R. 2001. Incidence and morphology of the brachioradialis accessorius muscle. Journal of Anatomy 199:353–355.

Rupke, N. A. 1993. Richard Owen's vertebrate archetype. Isis 84:231–251.

Shetty, P., Sirasanagandla, S. R., and Dsouza, M. R. 2014. Possible entrapment of sensory branch of radial nerve by split brachioradialis tendon:an anatomical variation. International Journal of Health Sciences and Research 4:204–207.

Schön, M. A. 1968. The muscular system of the red howling monkey. Bulletin of the United States National Museum 273:1–185.

Sirena, S. 1871. Recerche sulla miologia del Mycetes fuscus. Giornale di Scienze Naturali ed Economiche di Palermo. Part I. Scienze naturali 7:164–244.

Spinner, R. J., and Spinner, M. 1996. Superficial radial nerve compression at the elbow due to an accessory brachioradialis muscle: a case report. The Journal of Hand Surgery 21:369–372.

Vavilov, N. I. 1922. The law of homologous series in variation. Journal of Genetics 12:47–89.

Westling, C. 1889. Anatomische Untersuchungen über Echidna. Bihang till Kongliga Svenska Vetenskaps-Akademiens Handlingar 15:1–71.

Wood, J. 1867. On human muscular variations in their relation to comparative anatomy. Journal of Anatomy and Physiology 1:44–59.

Wood, V. E. 1988. The extensor carpi radialis intermedius tendon. Journal of Hand Surgery 13:242–245.

Youlatos, D. 1999. The schizodactylous grasp of the howling monkey. Zeitschrift für Morphologie und Anthropologie 82:187–198.

Youlatos, D. 2000. Functional anatomy of forelimb muscles in Guianan atelines (Platyrrhini: Primates). Annales des Sciences Naturelles — Zoologie et Biologie Animale 21:137–151.
How to Cite
NOVIKOVA, Mellin; KUZNETSOV, Alexander. An unusual elbow muscle in the red howler monkey: does it deserve invention of a new name musculus contrahens cubiti?. Biological Communications, [S.l.], v. 62, n. 1, p. 38–47, apr. 2017. ISSN 2542-2154. Available at: <>. Date accessed: 20 sep. 2017. doi:
Full communication