human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a head ...

, the extensor indicis roprius'' is a narrow, elongated

skeletal 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 m ...

in the deep layer of the dorsal

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in ...

, placed medial to, and parallel with, the

extensor pollicis longus In human anatomy, the extensor pollicis longus muscle (EPL) is a skeletal muscle located dorsally on the forearm. It is much larger than the extensor pollicis brevis, the origin of which it partly covers and acts to stretch the thumb together wi ...

. Its tendon goes to the

index finger The index finger (also referred to as forefinger, first finger, second finger, pointer finger, trigger finger, digitus secundus, digitus II, and many other terms) is the second digit of a human hand. It is located between the thumb and the mi ...

, which it extends.

Structure

It arises from the distal third of the dorsal part of the body of ulna and from the

interosseous membrane An interosseous membrane is a thick dense fibrous sheet of connective tissue that spans the space between two bones, forming a type of syndesmosis joint. Interosseous membranes in the human body: * Interosseous membrane of forearm The interosse ...

. It runs through the fourth tendon compartment together with the

extensor digitorum The extensor digitorum muscle (also known as extensor digitorum communis) is a muscle of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand. Extensor digitorum is innervated by the posterior int ...

, from where it projects into the dorsal

aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...

of the index finger. Opposite the head of the

second metacarpal The second metacarpal bone (metacarpal bone of the index finger) is the longest, and its base the largest, of all the metacarpal bones.'' Gray's Anatomy'' (1918). See infobox. Human anatomy Its base is prolonged upward and medialward, forming a ...

bone, it joins the ulnar side of the tendon of the extensor digitorum which belongs to the index finger. Like the

extensor digiti minimi The extensor digiti minimi (extensor digiti quinti proprius) is a slender muscle of the forearm, placed on the ulnar side of the extensor digitorum communis, with which it is generally connected. It arises from the common extensor tendon by a th ...

(i.e. the extensor of the little finger), the tendon of the extensor indicis runs and inserts on the ulnar side of the tendon of the common extensor digitorum. The extensor indicis lacks the juncturae tendinum interlinking the tendons of the extensor digitorum on the dorsal side of the hand.

Variation

The extensor indicis proprius does not show much variation. It exists as a single tendon most of the time. Double tendons of the extensor indicis proprius was also reported. It is known that the extensor indicis proprius inserts to the index finger on the ulnar side of the extensor digitorum. However, the insertion on the radial side of the common extensor digitorum infrequently seen, namely the ''extensor indicis radialis''. Split tendons of the muscle inserting on both ulnar and the radial side of the common extensor digitorum was also reported. Anomalous hand extensors including the extensor medii proprius and the extensor indicis et medii communis are often seen as variations of the extensor indicis due to the shared characteristics and embryonic origin.

Function

The extensor indicis extends the

, and by its continued action assists in extending (

dorsiflexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

) the

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...

and the

midcarpal joint The midcarpal joint is formed by the scaphoid, lunate, and triquetral bones in the proximal row, and the trapezium, trapezoid, capitate, and hamate bones in the distal row. The distal pole of the scaphoid articulates with two trapezial bones as ...

s. Because the index finger and little finger have separate extensors, these fingers can be moved more independently than the other fingers.

Additional images

Notes

References

* *

External links

* - "Extensor Region of Forearm and Dorsum of Hand: Deep Muscles of Extensor Region" * * * {{Authority control Muscles of the upper limb