An accessory muscle is a relatively rare

anatomical variation An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categ ...

where duplication of a

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

may appear anywhere in the

muscular system The muscular system is an organ system consisting of skeletal, smooth, and cardiac muscle. It permits movement of the body, maintains posture, and circulates blood throughout the body. The muscular systems in vertebrates are controlled through t ...

. Treatment is not indicated unless the accessory muscle interferes with normal function. Examples are the

sternalis muscle The sternalis muscle is an anatomical variation that lies in front of the sternal end of the pectoralis major parallel to the margin of the sternum. The sternalis muscle may be a variation of the pectoralis major or of the rectus abdominis. Struc ...

accessory soleus muscle The accessory soleus muscle is an accessory muscle of the calf which is rarely present in humans; it is, however, the most common accessory muscle of the ankle. The muscle inserts on the anterior aspect of the soleus muscle or on the posterior a ...

, extensor digitorum brevis manus and

epitrochleoanconeus muscle The epitrochleoanconeus muscle (anconeous epitrochlearis muscle, anconeus-epitrochlearis or anconeus sextus) is a small accessory muscle of the arm which runs from the back of the inner condyle of the humerus over the ulnar nerve to the olecranon ...

. An accessory muscle can also refer to a muscle that is not primarily responsible for movement but does provide assistance. Examples of such muscles are the accessory muscles of respiration where the

sternocleidomastoid 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 ...

and the

scalene muscles 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 an ...

(

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

, middle and posterior scalene) are typically considered accessory muscles of respiration.Netter FH. Atlas of Human Anatomy 3rd ed. Icon Learning Systems. Teterboro, New Jersey 2003 - plate 191

References

Muscular system {{muscle-stub

See also

References