Scalene Muscles

The scalene are lateral vertebral muscles which begin at the first and second ribs and pass up into the sides of the neck. There are three of these muscles. (1) The "scalenus anterior muscle," which, when the neck is fixed, elevates the first rib to aid in breathing or when the rib is fixed, bends the neck forward and sideways and rotates it to the opposite side. (2) The "scalenus medius" is similar to the scalenus anterior and raises the first rib from above or bends to slightly rotates the neck from below. (3) The "scalenus posterior" raises the second rib or bends and slightly rotates the neck. This muscle may be absent or may extend to the third rib. When the scalene muscles are fixed from above, they elevate the first and second ribs to become respiratory muscles for breathing. Acting from below, they bend the spinal column to the same side or, if muscles act on both sides, the spinal column is slightly flexed.

Very Scientific Version...

The scalenes vary in the number of their costal and vertebral attachments, as well as in the interrelationships caused by the fusion of numerous fasciculi. The problem of definition has been compounded by the
variety of descriptions of various muscles and their relation to the scalene mass by various authors. Frequently (about 30% of cases) a poorly defined muscle mass is present.

The anterior scalene is sometimes located behind the subclavian artery or it may be split into two parts for the arery to pass through between them. In such a case the muscle has been seen pierced by the
eighth cervical nerve dorsal to the artery. These are potential entrapment sites for the artery and the nerve. Bundles of muscle fibers may be exchanged between the anterior and the middle scalene. The
anterior scalene may also be closely associated with the anterior intertransverse muscles, and slips may be exchanged between them. The same is true in the case of longus capitis (rectus capitis anterior
major).

The muscle scalenus pleuralis (Sibson) or minimus (Albinus) is a frequent variation. When present this muscle arises from the transverse process of the seventh cervical vertebrae (occasionally also from
the the sixth), and extends to the inner border of the first rib and the fascia supporting the cervical dome of pleura. When absent the muscle is represented by a fibrous band (Sibson's fascia or the lig.
costo-pleuro-vertebralis of Zuckerkandl). Another variant, the transversalis cervicis medius, arises from the transverse processes of the second, and fourth cervical vertebrae and courses between the
middle and posterior scalenes to insert onto the seventh cervical and first thoracic vertebrae.

Typically the anterior scalene arises from the fourth, fifth and sixth cervical vertebrae (anterior tubercles), occasionslly from the third, and rarely from the seventh. When the anterior scalene is doubled, one of
them is termed accessory anterior scalene.

Mori found the anterior scalene arose from the anterior tuberculum of the transverse processes of cervical vertebrae as follows: from 2,3,4,5, on the right side and the left side, both 4 cases (3.3%); 3,4,5, on
the right side 53 times and on the left 55 times (45%); 4,5,6, on the right side 63 times and on the left 61 (51.6%) from 120 cadavers, 240 sides.

By vertebra of origin:

Second cervical, 8 sides, 33.3%,
Third cervical, 116 sides, 48.3%,
Fourth cervical, 240 sides, 100%,
Fifth cervical, 240 sides, 100%, and
Sixth cervical, 124 sides, 51.6%.

The tendon of all of Mori's cases inserted onto the scalenus tubercle on the upper surface of the body of the first rib, although it has been found to insert on the second or third ribs.

The middle scalene arises from the costotransverse lamellae of the lower five cervical vertebrae. It arises, in about 80% of cases, from the axis, in about 60% from the atlas, and in about 10% from the seventh
cervical vertebra.

The posterior scalene may arise from the third, fourth, and the seventh cervical vertebrae, as well as from the usual fifth and sixth; it inserts on the second and occasionally from the third rib. The posterior
scaleme is frequently fused with the middle scalene and the first external intercostal muscle. In Mori's cases (51 cadavers, 102 sides) scalenus posterior inserted as follows:

Rib 1; right side 9, left side 13, total 21, 21.5%.
Rib 1 and 2; right side 37, left side 34, total 71, 69.6%
Rib 1, 2, and 3; right side 5, left side 4, total 9, 8.8%.

The scalene muscles as a whole are considered as the intercostal muscles of the thorax, located in the neck. Owing to the absence of free ribs the three parts have merged and resemble the abdominal wall,
except that they do not have a distinct division between them.

Syn.: m. Sc. ant.: scalenus anticus, scalenus prior (Albinus), scalenus primus (Krause). Sc. med. : scalenus secundus. Sc. post. : scalenus tertius (Krause), scal&egravene posterieur.

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

Bochdalek, Jr. (1867) Vor dem Musculus sacalenus anticus ihren Verlauf nehmende Art. subclavia dextra. Arch. Path. Anat. Physiol. Klin. Med. 41:261-263.

Boyd, G.I. (1933-34) Abnormality of the subclavian artery associated with the presence of the scalenus minimus. J. Anat. 68:280-281.

Cave, A.J.E. (1933) A note on the origin of the m. scalenus medius. J. Anat. 67:480-483.

Fawcett, E. (1896) What is Sibson's muscle (scalenus pleuralis)? J. Anat. Physiol. 30:433-436.

Gilis, P. (1891) Note sur l'anatomie des muscles scal&egravenes. Soc. Biol., Comptes Rendus Hebdomadaires des S&eacuteances et M&eacutemories. 43:223-226.

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

Iwate, S. (1930) On the scalenus minimus. Juzenkai Zasshi. 35:2567-2574. In Japanese.

Kirgis, H.D. and A.F. Reed. (1948) Significant anatomic relationsin the syndrome of the scalene muscles. Ann. Surg. 127:1182-1201.

Latarjet, A. (1948) Testut's Trait d'Anatomie Humaine, 9th ed.. G. Doin & Cie., Paris.

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.

Mori, M. (1964) Statistics on the musculaturre of the Japanese. Okajimas Folia Anatomica Japonica. 40:195-300.

Nat, B.S. (1924) The scalenus muscle. J. Anat. 58:268-270.

Nishi, S. (1916-17) Report of the dissection in the Tohoku medical college. Tohoku Igakkai Zasshi. 1:64-66, 392-396. In Japanese.

Nishi, S. (1953) Miologie de la japano. Statistika raporto pri muskolanomalioj ce japanoj. The Gunma Journal of Medical Sciences 2:1-13. In Japanese.

Nishi, S. (1953) Statistics studies on the spinal musculature. The Gunma Journal of Medical Science. 2:109-121, 187-205. In Japanese.

Schaefer, E. A., Symington, J. and T.H. Bryce., Eds. (1923) Quain's Elements of Anatomy, 11th ed. , Longmans, Green and Co., London.

Sebileau, P. (1891) Le muscle scal&egravene. Soc. Biol., Comptes Rendus Hebdomadaires des S&eacuteances et M&eacutemoires. 43:201-221.

Shore, L.R. (1926) An example of the muscle scalenus minimus. J. Anat. 60:418-419.

Stott, C. F. (1928) A note on the scalenus minimus muscle. J. Anat. 65:359-361.

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