Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: S
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
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), scalène posterieur.
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Bartanuszova, M. and Williams, V. and Moore, C.M. A rare case of the thyrocervical trunk piercing the anterior scalene muscle bilaterally. International Journal of Anatomical Variations (2016) 9: 18–20.
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