An accessory muscle is a relatively rare

anatomical variation An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with Morphology (biology), morphological features different from those that are typically described in the majority of individuals. Anatomica ...

where duplication of a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

may appear anywhere in the

muscular system The muscular system is an organ (anatomy), organ system consisting of skeletal muscle, skeletal, smooth muscle, smooth, and cardiac muscle, cardiac muscle. It permits movement of the body, maintains posture, and circulates blood throughout the bo ...

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

Examples

Examples are the accessory soleus muscle in the calf or ankle, the extensor digitorum brevis manus in the hand and epitrochleoanconeus muscle of the upper arm. Additional examples in the hand include Flexor carpi radialis brevis which can compress the anterior interosseous nerve. Also see palmaris profundus muscle. On the extensor side: extensor digitorum brevis manus,
extensor carpi radialis intermedius

extensor medii proprius muscle The extensor medii proprius (so called the ''extensor digiti medii'') is a rare anatomical variant in the extensor compartment of the forearm. The aberrant muscle is analogous to the extensor indicis with the insertion being the middle finger ins ...

Accessory muscles of the anterior thoracic wall include the sternalis muscle, the axillary arch (Langer's), variations of pectoralis major such as the ''pectoralis minimus'', ''pectoralis quartus'', and ''pectoralis intermedius'', the ''chondrocoracoideus'' and ''chondrofascialis''. The whole pectoral region is subject to a high degree of variability. The pectoralis major or pectoralis minor may be absent, or in some cases the pectoralis major may be doubled. Other variants noted in this region are the ''chondroepitrochleas'' originating in one or more ribs, or directly from the pectoralis major; the ''costocoracoideus'' from the 6th to 8th ribs, and a ''chondrocoracoideus'' and another variant of this waiting to be named. Most of these accessory muscles are implicated in neurovascular compression. Of clinical use the newly described ''chondrocoracoideus'' has potential for use in reconstructive surgery. Axillary accessory muscles may be encountered in axillary lymph node removal, the awareness of which could avoid complications. 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 The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration duri ...

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 acces ...

and the scalene muscles (

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

, 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 Muscular system

Examples

See also

References