Levator claviculae muscle
Encyclopedia
In human anatomy
, the levator claviculae is a very rare accessory
and vestigial
skeletal muscle
in the posterior triangle of the neck
. It originates on the transverse processes of the upper cervical vertebrae
and is inserted in the lateral half of the clavicle
. Though a supernumerary
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.
and levator scapulae muscle
s but medial to the sternocleidomastoid muscle
. 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
before its insertion.
It has been reported to originate on the sixth cervical vertebra.
, 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 trapezius
, the scalenus anterior, and the longus colli
, but is possibly derived from an additional segmentation of the ventrolateral muscle primordia of the neck.
Uncommon in human anatomy, the levator claviculae is nearly always present in most other mammals — including gibbons
, orangutan
s, and chimpanzee
s. There are yet no phylogenetic explanations for its absence in humans.
, 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.
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
, the levator claviculae is a very rare accessory
Accessory
Accessory may refer to:* Accessory , a person who assists a criminal but is not present at the crime* Accessory , with members Dirk Steyer and Ivo Lottig* Fashion accessory, i.e...
and vestigial
Human vestigiality
In the context of human evolution, human vestigiality involves those characters occurring in the human species that are considered vestigial—in other words having lost all or most of their original function through evolution...
skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
in the posterior triangle of the neck
Posterior triangle of the neck
-Boundaries:It has the following boundaries:Apex: Union of the sternocleidomastoid and the trapezius muscles at the superior nuchal line of the occipital boneAnterior: Posterior border of the sternocleidomastoideus...
. It originates on the transverse processes of the upper cervical vertebrae
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...
and is inserted in the lateral half of the clavicle
Clavicle
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
. Though a supernumerary
Supernumerary
A Supernumerary is an additional member of an organization. A supernumerary is also a non-regular member of a staff, a member of the staff or an employee who works in a public office who is not part of the manpower complement...
muscle present in only 2-3% of all people, it is not an abnormality but a variant of normal human anatomy with an atavistic
Atavism
Atavism is the tendency to revert to ancestral type. In biology, an atavism is an evolutionary throwback, such as traits reappearing which had disappeared generations before. Atavisms can occur in several ways...
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.
Origin and insertion
Its origin is on at least the third uppermost vertebrae, from where it courses inferiorly and laterally, lateral to the scaleneScalene muscles
The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the scalenus anterior, scalenus medius, and scalenus posterior.They are innervated by the spinal nerves C4-C6....
and levator scapulae muscle
Levator scapulae muscle
In human anatomy, the levator scapulae is a skeletal muscle situated at the back and side of the neck. As the name suggests, its main function is to lift the scapula.-Origin and insertion:...
s but medial to the sternocleidomastoid muscle
Sternocleidomastoid muscle
In human anatomy, the sternocleidomastoid muscle , also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck...
. 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
Trapezius muscle
In human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula...
before its insertion.
It has been reported to originate on the sixth cervical vertebra.
Occurrence
The levator claviculae is an infrequently recognized anatomical variant in humans, distinguished from, for example, cervical adenopathy or a thrombosed veinThrombosis
Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...
, 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
Sternocleidomastoid muscle
In human anatomy, the sternocleidomastoid muscle , also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck...
, the trapezius
Trapezius muscle
In human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula...
, the scalenus anterior, and the longus colli
Longus colli muscle
The Longus colli muscle 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....
, but is possibly derived from an additional segmentation of the ventrolateral muscle primordia of the neck.
Uncommon in human anatomy, the levator claviculae is nearly always present in most other mammals — including gibbons
Gibbons
Notable people named Gibbons include:* Alan Gibbons, a British author* Beth Gibbons , a British singer* Billy Gibbons, a guitarist for ZZ Top* Carroll Gibbons , an American-born British bandleader...
, orangutan
Orangutan
Orangutans are the only exclusively Asian genus of extant great ape. The largest living arboreal animals, they have proportionally longer arms than the other, more terrestrial, great apes. They are among the most intelligent primates and use a variety of sophisticated tools, also making sleeping...
s, and chimpanzee
Chimpanzee
Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
s. There are yet no phylogenetic explanations for its absence in humans.
History of research
The first documented observation of the levator claviculae occur in an anatomical drawing by Leonardo da VinciLeonardo da Vinci
Leonardo di ser Piero da Vinci was an Italian Renaissance polymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer whose genius, perhaps more than that of any other figure, epitomized the Renaissance...
, but the first documented case was not reported until 1813. Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
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
Robert Wiedersheim
Robert Wiedersheim was a German anatomist who is famous for publishing a list of 86 “vestigial organs” in his book 'The Structure of Man: An Index to His Past History'....
included it in his list of 86 vestigial organs.