Lesson 7 Ecorche - The Forearm and Hand


    -Grouped Extensors

    -Extensor carpi radialis brevis


    -Grouped Flexors

    -Brachioradialis + Extensor Carpi radialis longus 

    -Thumb muscles of the wrist, radius side


    -Pad under knuckles

    -Palm tissues of the thumb side

    -Palm tissues of the little finger side

    -1st dorsal interosseus

    -Finger soft tissue volumes


-The take home message is that the forearm is divided by the ulna and radius into the extensor group (on the outside) and the flexor group (on the inside).  At the proximal (closest to the body) end of the forearm, where the radius is not visible, the brachioradialis and Extensor Carpi Radialis Longus form a mass that separates the rest of the extensors from the flexors.

-On the scale of the model you are working on here, it is not possible to place all the detail in the forearm and hand - even the simplified version presented here, the diagrams present information to help explain the surface anatomy we will observe in the model.

Attachments to bones

(Diagrams from Gray's Anatomy)


Ulna and Radius


Grouped extensors

-This group is on the outer surface of the plane made by the radius and ulna.

-The main mass of muscle is located towards elbow

-In this group we are including the following superficially visible muscles:

    - Extensor carpi ulnaris

    - Extensor digitorum

    - Extensor digitorum minimi

    - Extensor policis longus

- The tendons of these muscles are shown crossing the back of the hand, where they are most visible in the living figure that we observe (The tendons of the Extensor digitorum and Extensor policis longus actually do extend out into the distal phalanges (ends of the fingers) along the back of the fingers, but this is not usually very visible) 



Lateral Epicondyle of the humerus



Various points on the hand and fingers


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Extensors of the left arm (Extended and pronated)

Extensors of the right arm (Flexed and supinated)

 Notice in this arm that the extensor group is pulled into a spiral with supination (outwards rotation) of the hand.

Extensor carpi Radialis Brevis

This muscle has been distinguished from the other extensor muscles because it is often visible in the living model distinct from both the Extensor Carpi Radialis Longus that lies across it, and the other forearm extensors that lie beside it.



Lateral epicondyle of Humerus



3rd Metacarpal


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Small triangular muscle crossing the elbow joint on the outside.


Lateral epicondyle of Humerus



posterior olecranon process of ulna (distal to attachment of triceps attachment)


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Grouped flexors

-This group includes:

    - Pronator teres

    - Flexor carpi radialis

    - Palmaris longus

    - Flexor carpi ulnaris


- separated from the Extensors by the ulna and the radius

- the bulk of this group is greater than the extensors since it provides the power for clasping movements

-note the second tendon of the Biceps brachilais inserting across the Flexors, deforming the shape and thereby contributing to the shape of this muscle group



Medial epicondyle of humerus



hand and wrist (tendons are on inside of wrist)


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Grouped flexors of the left arm

Grouped flexors of the right arm

Extensor carpi radialis longus

-Together with the Bracchioradialis, the Extensor carpi radialis longus forms a flame like volume wrapping from the outside of the humerus above the lateral epicondyle, towards the radial side of the forearm, with its bulk finishing about half way down the radius



Lateral humerus above epicondyle



Extensor carpi radialis longus: 2nd metacarpal


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Dark Blue



- the Bracchioradialis approximately follows the path of the Extensor Carpi Radialis Longus, but begins slightly higher on the humerus, with the bulk finishing slightly lower on the forearm. 


Lateral humerus above extensor carpi radialis longus 



Bracchioradialis: lateral side of distal end of radialis



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Combined mass of the Extensor carpi radialis longus and Bracchioradialis:

Thumb muscles of the wrist


This group includes

    -Abductor policis longus

    -Extensor policis brevis


-Sliding between the Extensor digitorum and and Extensor carpi radialis brevis, this pair of muscles contributes to the form of the wrist

- Along with the tendon of the Extensor policis longus (included in the extensor group) the tendons of this pair contribute to the squareness of the end of the Radius bone, and distal to this form the “snuff box”, the groove between these tendons where they cross the wrist.



The origins of both muscles are tucked out of view under the Extensor digitorum, on radius and ulna



-Extensor policis brevis: base of the proximal phalanx of the thumb (just distal to the first thumb joint)

-Abductor policis longus: base of the first metacarpal


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Lateral aspect of the left arm

(Extended, pronated)


Medial aspect of the left arm 

(Extended, pronated)


Lateral aspect of the right arm

(Flexed, supinated)


Medial aspect of the right arm

(Flexed, supinated)

Volumes of the palm

Pad under the knuckles

-Notice how this volume extends beyond the first row of knuckles of the hand


Palm soft tissues on the little finger side

- Includes the Palmaris brevis, Flexor digiti minimi, Abductor digit minimi plus other soft tissues

Triangle of Thumb "Knuckle" - Palm soft tissues on the thumb side and 1st Interosseus

-Includes the Abductor policis brevis, Adductor pollicis transverse,  Opponens pollicis plus other soft tissues

- The Palm soft tissues on the thumb side and 1st Interosseus form a triangular mass that bridges the space from the side of the 1st metacarpal to the thumb "Knuckle" (joint where the thumb itself emerges from the palm mass).  The mobility of this joint means that the triangle moves relative to the oblong mass of the finger metacarpals substantially

Pads and soft tissues of the fingers and thumb

-As for the toes, the fingers and thumbs themselves don’t contain muscles

-The bones and tendons that run down the back and front face of the digits are protected by soft tissues, notably the fatty pads on the palm side, that form the characteristic pads of the fingers between the joints.

- Note that the thumb, like the big toe, has only one joint past the joint at the palm, whereas the fingers, like the small toes, have two.

- The form of the finger on the dorsal face are largely created by the square forms of the joints between cylindrical volumes of the bone between, and sometimes the tendons running over the joint

- Note the pentagonal shape of the palm that includes the tapering block of the metacarpals of the fingers and the triangle that reaches out to the first thumb joint.  You can think of the palm region of the hand as essentially a pentagonal volume that folds at the border between these masses.

- Note that when 

Characteristic forms of hand

    - "Knuckle" of thumb more mobile that the knuckles of the fingers and it is located about half way along metacarpals

    - alignment curves of knuckles and finger joints

    - turn in of index finger and little finger

- the metacarpal joints at the knuckles allow sideways splaying out of the fingers

- The joints of the phalanges are more square than this, and like the knee joint allow articulation in only one plane.  Also like the knee, the square shape creates important boxiness to the joint, particularly the 1st finger joint.  each of the finger joints is interspersed with more round, curving volumes between

- The 1st joint naturally bends slightly more than the second joint of the fingers as the fingers close.  This can be overcome by certain muscle contractions, resulting in a claw-like appearance, and requiring effort