In human anatomy, the extensor indicis roprius'' is a narrow, elongated skeletal muscle 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 w ...

. 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 mid ...

, which it extends.

Structure

It arises from the distal third of the dorsal part of the

body of ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of the ...

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 * Interosseou ...

. 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 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 thi ...

(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 In human anatomy, juncturae tendinum or ''connexus intertendinei'' refers to the connective tissues that link the tendons of the extensor digitorum communis, and sometimes, to the tendon of the extensor digiti minimi. Juncturae tendinum are locat ...

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 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 inst ...

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 carp ...

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 a ...

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