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

Sternocleidomastoideus

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed


Comparative anatomical studies have concluded the the sternocleidomastoid muscle is composed of five parts arranged in two layers. The amount of fusion of the two heads of this muscle varies considerably. They are frequently separated into cleidomastoid and sternomastoid parts; this has been regarded as normal by some authors. In addition, the muscle frequently separates into other parts, which are arranged in two layers: a superficial layer consisting of a superficial sternomastoid, sterno-occipital, and a cleidooccipital part, and a deep layer consisting of a deep sternomastoid and a cleidomastoid part. To these five parts a sixth has been seen and described as sternomastoideus profundus. The names adequately indicate the attachments of the various parts.

 

Mori reported the the two heads, sternal and clavicular, are independent or distinct in 88.6% of Japanese subjects (450/510 individuals). The space between the two heads is triangular is filled with fascia, and named trigonum supraclavicularis minor and covered by cervical fascia.

Mori also reported that the superficial and deep layers are rarely independent of each other. In 1020 sides, only 10 instances (1%) of complete separation was found. The independence of the cleidooccipital portion was found in 102 (10.9%) of 1020 body sides (510 cadavers), and this only near its insertion on the occipital bone.

A supernumerary cleidooccipital (Wood), more or less separate from the sternocleidomastoid, has a reported frequency of 33%.

Occasionally, the lower portion of the muscle is traversed by a tendinous intersection, a peculiarity of interest in connection with the formation of the muscle by the fusion of parts derived from different myotomes.

In many animals, the cleidomastoid portion of the muscle is quite distinct from the sternomastoid portion; this condition is frequently found in humans. Other variants of cleidomastoideus include cleidoepistrophicus, which originates from the second cervical vertebra and inserts on the clavicle adjacent to the sternocleidomastoid; cleidocervicalis which originates from the carotid tubercle of the fourth cervical vertebra and inserts on the clavicle adjacent to sternocleidomastoid; and cleidoatlanticus, which originates from the transverse process of the atlas and inserts on the clavicle about 2cm. away from cleidomastoideus.

The width of the clavicular portion of the muscle varies greatly. The origin of sternocleidomastoideus may spread from the acromial to the sternal end of the clavicle. the sternal head has been seen to extend as far distally as the junction of the fifth rib.

Slips from the muscle may pass to neighboring structures, e.g., the parotid fascia, thyroid cartilage , the angle of the mandible, and contralateral clavicle, and slips have been found arising from the anterior tubercles of the transverse process of the upper three cervicle vertebrae and from the hyoid bone. Various aberrant bundles have been described ending in various ways. Such a slip from the mastoid process terminating on the fascia of the carotid sheath, a slip from the deep surface extending to the cartilago triticea, which has also been associated with a bundle to the hyoglossus muscle. A slip may be given to the tympanic bone, stylomandibular ligament, or mandible at its angle. This last attachment is similar to that in ungulates where it normally occurs. Gruber has reported a variety, also seen in the orangutan and chimpanzee, where the muscle attaches to the transverse process of the axis instead of the mastoid process.

The entire muscle may be doubled or absent.

Syn.: m. nutator capitis (Meckel), mastoideus colli (Arnold), Kopfnicker.

Image 193

Sternocleidomastoid Muscle.
redrawn from Piersol's Human Anatomy,
J.B. Lippincott Company, Philadelphia, 1930.

Image 164

Varieties of Chest, Neck, and Shoulder Muscles-Sternomastoideus.
modified and redrawn from Wood.

Image 174

Varieties of Chest, Neck, and Shoulder Muscles-Cleidomastoideus.
modified and redrawn from Wood.

Image 180.

Varieties of Chest, Neck, and Shoulder Muscles-Cleidooccipitalis.
modified and redrawn from Wood.

Image 150

Cleidoatlanticus.
from Haffner.


References

Anonymous, -. (1922) Anatomie du vivant. Attitudes vicieuses du cou d'origine musculaire. La Presse Médicale. No. 76. 30:1594.

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

Gruber, W. (1876) Ein musculus cleido-cervicalis s. tracheloclavicularis imus. Arch. Anat. Physiol. Wissen. Med. 1876:757-758.

Gruber, W. (1876) Vorkommen des Musculus cleido-mastoideus als Musculus cleido-epistrophicus. Arch. Anat. Physiol. Wissen. Med. 1876:759-760.

Gruber, W. (1876) Ein Musculus cleido-atlanticus. Arch. Anat. Physiol. Wissen. Med. 1876:761.

Gruber, W. (1885) Supernumerärer Bauch des Musculus sternocleidomastoideus in der Richtung des hinteren Bauches des M. digastricus maxillae inferioris und abwärts von diesem zum Os hyoides. Arch. Path. Anat. Physiol. Klin. Med. 102:538-539.

Gruber, W. (1885) Ein Musculus cleido-occipitalis mit enorm breiter Endaposeurose. Arch. Path. Anat. Physiol. Klin. Med. 102:539-540.

von Haffner, H, (1903) Eine Seltene doppelseitige Anomalie des Trapezius. Internat. Monatsschrift für Anat. Physiol. 20:313-318.

Henle, J. (1871) Handbuch der Muskellehre des Menschen, in Handbuch der systematischen Anatomie des Menschen. Verlag von Friedrich Vieweg und Sohn, Braunschweig.

Koura, K. (1959) Anatomical studies on the cervical muscles (M. sternocleidomastoideus, M. sternohyoideus and M. omohyoideus. Shika Gakuho 59:1231.

Krause, W. (1876) Der M. sternocleidomastoideus. Centralblatt Med. Wissen. 1876:433-435.

Macalister, A. (1875) Observations on the 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.

Miyauchi, R. (1983) A rare anomalous muscle of the neck; A case with the Supernumerärer Bauch des Musculus sternocleidomastoideus (Gruber). Okajimas Folia Anatomica Japonica 60:187-194.

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

Ouchi, H. (1953) On the variation of the muscles (M. sternocleidomastoidens (sic), M. flexor digitorum brevis, M. quadratus plantae). Kaibogaku Zasshi. 28:Supple. Kanto 9-10. In Japanese.

Richet, -. (1873) Anomalies musculaires: sterno-cléïdo-mastoïden et l'omoplateo-hyoidïen. Bulletins et Mem. de la Société anatomique de Paris XLVIII(2):137.

Schaefer, E.A., Symington, J. and T.H.Bryce., Eds, (1923) Quain's Elements of Anatomy. Longmans, Green and Co. London.

Shima, H. and K. Ichikawa. (1956) Anatomical studies on the M. sternocleidomastoideus. Tokyo Shikadaigaku Kaibogakukyoshitsu Gyosekishu 1:6-9. In Japanese.

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