In human anatomy, the levator claviculae is a very rare accessory and

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

skeletal muscle in the

posterior triangle of the neck Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to its head ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability The posterior probability is a type of conditional probability that r ...

. It originates on the transverse processes of the upper cervical vertebrae and is inserted in the lateral half of the

clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the r ...

. Though a

supernumerary Supernumerary means "exceeding the usual number". Supernumerary may also refer to: * Supernumerary actor, a performer in a film, television show, or stage production who has no role or purpose other than to appear in the background, more commonl ...

muscle present in only 2–3% of all people, it is not an abnormality but a variant of normal human anatomy with an atavistic character. It has also been referred to as the omocervicalis, cleidocervicalis, and tracheloacromial muscle, with the variation in names indicating different sites of origin and insertion.

Structure

Its origin is on at least the third uppermost vertebrae, from where it courses inferiorly and laterally, lateral to the scalene and

levator scapulae muscle The levator scapulae is a slender skeletal muscle situated at the back and side of the neck. As the Latin name suggests, its main function is to lift the scapula. Anatomy Attachments The muscle descends diagonally from its origin to its inserti ...

s but medial to the

sternocleidomastoid muscle The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the access ...

. Passing posteriorly to the latter muscle, it is inserted either to the middle of the clavicle or, more frequently, to the lateral third of the clavicle. It might also blend with the

trapezius The trapezius is a large paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It moves the scapula and supports th ...

before its insertion. It has been reported to originate on the sixth cervical vertebra.

Variation

The levator claviculae is an infrequently recognized anatomical variant in humans, distinguished from, for example, cervical

adenopathy Lymphadenopathy or adenopathy is a disease of the lymph nodes, in which they are abnormal in size or consistency. Lymphadenopathy of an inflammatory type (the most common type) is lymphadenitis, producing swollen or enlarged lymph nodes. In cl ...

or a thrombosed vein, but a normal muscle in lower mammals and anthropoids. In humans, when present, it often appears unilaterally, most commonly on the left side, or bilaterally. The embryologic origin of the muscle is controversial and subject to numerous hypotheses. It has been proposed to originate from several neighbouring muscles, including the sternocleidomastoid, the

, the

scalenus anterior The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the anterior scalene, middle scalene, and posterior scalene. They are innervated by the third to the eight cervical spinal nerves (C3-C8). The anterior and m ...

, and the

longus colli The longus colli muscle (Latin for ''long muscle of the neck'') is a muscle of the human body. The longus colli is situated on the anterior surface of the vertebral column, between the atlas and the third thoracic vertebra. It is broad in the mid ...

, but is possibly derived from an additional segmentation of the ventrolateral muscle

primordia A primordium (; plural: primordia; synonym: anlage) in embryology, is an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable o ...

of the neck. Uncommon in human anatomy, the levator claviculae is nearly always present in most other mammals — including gibbons,

orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genu ...

s, and chimpanzees. There are yet no

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

explanations for its absence in humans.

History

The first documented observation of the levator claviculae occurs in an anatomical drawing by

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially res ...

, but the first documented case was not reported until 1813. Darwin briefly described the muscle as an example of many muscles "found in all kinds of apes" but rare in humans. About the same time, Huxley and Wood reported the muscle has a predominantly unilateral occurrence. Since then only a dozen cases have been reported and the traditional 2–3% ratio, attributed to Wood, is possibly an overestimation not clearly corroborated by recent research. German anatomist Robert Wiedersheim included it in his list of 86

vestigial organs Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

References

Books

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{{Muscles of neck Muscles of the upper limb