Radius
M
RiGHT M
vina
HAND
Scaphoid
1
> Lunate
Trapezium S
>
Trique trum
> Pisiform
Trapezoid /
> Hamate
Capitate (
Metacarpal -
Sesamoid bone < ↑
Metacarpal
Proximal phalange <
Distal phalange (
Proximal phalange
1
Middle phalanges
Distal
phalanges
S
·
5
2
3 4
,BONES OF FOREARM
The two bones of the forearm function together as the second part of a flexible, articulated
strut—the first part being the humerus—with the shoulder serving as a mobile base that
positions the hand. Because the forearm is made up of two parallel bones, and the radius is
able to pivot around the ulna, supination and pronation are possible. This allows the hand to
rotate, particularly when the elbow is flexed.
ULNA
The ulna is the stabilizing bone of the forearm and is located on the medial side. It is the
longer of the two forearm bones. Its proximal end is more robust and is specialized for
articulation with the humerus above and the head of the radius laterally.
For articulation with the humerus, the ulna has two prominent projections:
1. The olecranon, which extends upward from the posterior side and forms the point of
the elbow, acting as a lever for elbow extension.
2. The coronoid process, which projects forward from the anterior side.
These two processes form the walls of the trochlear notch, which resembles the jaws of a
wrench and articulates with the trochlea of the humerus. This articulation mainly permits
flexion and extension at the elbow joint, though slight abduction and adduction may occur
during pronation and supination of the forearm.
Just below the coronoid process is the ulnar tuberosity, where the brachialis muscle
attaches.
On the lateral side of the coronoid process is the radial notch, a smooth concavity that
receives the edge of the head of the radius. Below this, on the lateral surface of the ulnar
shaft, is a raised ridge called the supinator crest. Between this crest and the lower part of the
coronoid process lies the supinator fossa. Both the crest and the fossa serve as attachment
points for the deep part of the supinator muscle.
The shaft of the ulna is thick and cylindrical near the top but tapers as it moves distally. At its
distal end, the ulna features a small, disc-shaped head with a pointed projection known as the
ulnar styloid process. Notably, the ulna does not extend to the wrist joint and does not
participate in the radiocarpal (wrist) joint.
,RADIUS
The radius is the lateral and shorter of the two bones of the forearm. Its proximal end
consists of a head, neck, and a medially directed radial tuberosity.
The head of the radius has a smooth, concave upper surface that articulates with the
capitulum of the humerus, allowing for flexion and extension at the elbow joint. The outer
edge of the head also articulates with the radial notch of the ulna, and the entire surface of the
head is covered in articular cartilage to support both movements and articulation.
Just below the head is the neck of the radius, a narrowed region leading into the radial
tuberosity, which lies on the medial side and marks the transition from the proximal end to the
shaft. The radial tuberosity serves as the insertion site for the biceps brachii tendon.
Unlike the ulna, the shaft of the radius gradually widens as it approaches the distal end.
When viewed in cross-section, the distal radius appears four-sided. Its medial side contains
the ulnar notch, which accommodates the head of the ulna, while the lateral side tapers into
the radial styloid process, a projection that is longer than the ulnar styloid process and
extends more distally—an important detail in clinical settings, especially in fractures.
On the dorsal side of the distal radius is the dorsal tubercle, which serves as a pulley for the
tendons of several forearm muscles, separating their shallow grooves.
The shafts of both the radius and ulna are generally triangular in cross-section, with a
rounded, superficial base and a sharp, deep apex. The apex is defined by the interosseous
border, which gives attachment to the interosseous membrane—a thin fibrous sheet
connecting the two bones. Most fibers of this membrane run obliquely from the radius
downward and medially to the ulna, allowing it to transmit forces received by the radius
(from the hand) to the ulna, and then upward toward the humerus.
BONES OF HAND
The wrist, or carpus, is made up of eight carpal bones arranged in two rows—proximal and
distal, each containing four bones. These small bones contribute to the flexibility and mobility
of the wrist. Structurally, the carpus is convex posteriorly and concave anteriorly. Movement
between the carpal bones is achieved through gliding—both between the two rows and
between adjacent individual bones—enhancing overall wrist motion.
Proximal Row of Carpal Bones (lateral to medial):
● Scaphoid: A boat-shaped bone that articulates proximally with the radius and features
a prominent scaphoid tubercle; it is the largest bone in the proximal row.
● Lunate: A crescent-shaped bone situated between the scaphoid and triquetrum; it also
articulates with the radius and is wider anteriorly than posteriorly.
, ● Triquetrum: A pyramidal bone on the medial side of the carpus; it articulates with the
articular disc of the distal radioulnar joint.
● Pisiform: A small, pea-shaped bone located on the palmar surface of the triquetrum.
Distal Row of Carpal Bones (lateral to medial):
● Trapezium: A four-sided bone on the lateral side of the wrist; it articulates with the 1st
and 2nd metacarpals, scaphoid, and trapezoid bones.
● Trapezoid: A wedge-shaped bone similar to the trapezium; it articulates with the 2nd
metacarpal, trapezium, capitate, and scaphoid.
● Capitate: The largest carpal bone, with a rounded head-like structure; it articulates
mainly with the 3rd metacarpal, as well as with the trapezoid, scaphoid, lunate, and
hamate.
● Hamate: A wedge-shaped bone on the medial side of the wrist, articulating with the 4th
and 5th metacarpals, capitate, and triquetrum. It features a prominent hook-like
projection, the hook of the hamate, which points anteriorly.
The proximal surfaces of the distal carpal bones articulate with the proximal row, and their
distal surfaces articulate with the metacarpals.
Metacarpus
The metacarpus forms the bony framework of the palm, lying between the carpus and the
phalanges. It consists of five metacarpal bones, each with a base (proximal), shaft, and
head (distal).
● The bases articulate with the carpals, and the heads articulate with the proximal
phalanges, forming the knuckles.
● The 1st metacarpal (thumb) is the shortest and thickest.
● The 3rd metacarpal is distinguished by a styloid process on the lateral side of its base.
Phalanges
Each finger (digit) has three phalanges—proximal, middle, and distal—except the thumb,
which has only two(proximal and distal).
● The phalanges of the thumb are broader and stronger than those of the other digits.
● Each phalanx consists of a base, a shaft, and a head.
● The proximal phalanges are the largest, the middle phalanges are intermediate, and
the distal phalanges are the smallest.
● The shafts taper toward the distal end, and the terminal phalanges are flattened and
expanded at their ends to support the nail beds.
M
RiGHT M
vina
HAND
Scaphoid
1
> Lunate
Trapezium S
>
Trique trum
> Pisiform
Trapezoid /
> Hamate
Capitate (
Metacarpal -
Sesamoid bone < ↑
Metacarpal
Proximal phalange <
Distal phalange (
Proximal phalange
1
Middle phalanges
Distal
phalanges
S
·
5
2
3 4
,BONES OF FOREARM
The two bones of the forearm function together as the second part of a flexible, articulated
strut—the first part being the humerus—with the shoulder serving as a mobile base that
positions the hand. Because the forearm is made up of two parallel bones, and the radius is
able to pivot around the ulna, supination and pronation are possible. This allows the hand to
rotate, particularly when the elbow is flexed.
ULNA
The ulna is the stabilizing bone of the forearm and is located on the medial side. It is the
longer of the two forearm bones. Its proximal end is more robust and is specialized for
articulation with the humerus above and the head of the radius laterally.
For articulation with the humerus, the ulna has two prominent projections:
1. The olecranon, which extends upward from the posterior side and forms the point of
the elbow, acting as a lever for elbow extension.
2. The coronoid process, which projects forward from the anterior side.
These two processes form the walls of the trochlear notch, which resembles the jaws of a
wrench and articulates with the trochlea of the humerus. This articulation mainly permits
flexion and extension at the elbow joint, though slight abduction and adduction may occur
during pronation and supination of the forearm.
Just below the coronoid process is the ulnar tuberosity, where the brachialis muscle
attaches.
On the lateral side of the coronoid process is the radial notch, a smooth concavity that
receives the edge of the head of the radius. Below this, on the lateral surface of the ulnar
shaft, is a raised ridge called the supinator crest. Between this crest and the lower part of the
coronoid process lies the supinator fossa. Both the crest and the fossa serve as attachment
points for the deep part of the supinator muscle.
The shaft of the ulna is thick and cylindrical near the top but tapers as it moves distally. At its
distal end, the ulna features a small, disc-shaped head with a pointed projection known as the
ulnar styloid process. Notably, the ulna does not extend to the wrist joint and does not
participate in the radiocarpal (wrist) joint.
,RADIUS
The radius is the lateral and shorter of the two bones of the forearm. Its proximal end
consists of a head, neck, and a medially directed radial tuberosity.
The head of the radius has a smooth, concave upper surface that articulates with the
capitulum of the humerus, allowing for flexion and extension at the elbow joint. The outer
edge of the head also articulates with the radial notch of the ulna, and the entire surface of the
head is covered in articular cartilage to support both movements and articulation.
Just below the head is the neck of the radius, a narrowed region leading into the radial
tuberosity, which lies on the medial side and marks the transition from the proximal end to the
shaft. The radial tuberosity serves as the insertion site for the biceps brachii tendon.
Unlike the ulna, the shaft of the radius gradually widens as it approaches the distal end.
When viewed in cross-section, the distal radius appears four-sided. Its medial side contains
the ulnar notch, which accommodates the head of the ulna, while the lateral side tapers into
the radial styloid process, a projection that is longer than the ulnar styloid process and
extends more distally—an important detail in clinical settings, especially in fractures.
On the dorsal side of the distal radius is the dorsal tubercle, which serves as a pulley for the
tendons of several forearm muscles, separating their shallow grooves.
The shafts of both the radius and ulna are generally triangular in cross-section, with a
rounded, superficial base and a sharp, deep apex. The apex is defined by the interosseous
border, which gives attachment to the interosseous membrane—a thin fibrous sheet
connecting the two bones. Most fibers of this membrane run obliquely from the radius
downward and medially to the ulna, allowing it to transmit forces received by the radius
(from the hand) to the ulna, and then upward toward the humerus.
BONES OF HAND
The wrist, or carpus, is made up of eight carpal bones arranged in two rows—proximal and
distal, each containing four bones. These small bones contribute to the flexibility and mobility
of the wrist. Structurally, the carpus is convex posteriorly and concave anteriorly. Movement
between the carpal bones is achieved through gliding—both between the two rows and
between adjacent individual bones—enhancing overall wrist motion.
Proximal Row of Carpal Bones (lateral to medial):
● Scaphoid: A boat-shaped bone that articulates proximally with the radius and features
a prominent scaphoid tubercle; it is the largest bone in the proximal row.
● Lunate: A crescent-shaped bone situated between the scaphoid and triquetrum; it also
articulates with the radius and is wider anteriorly than posteriorly.
, ● Triquetrum: A pyramidal bone on the medial side of the carpus; it articulates with the
articular disc of the distal radioulnar joint.
● Pisiform: A small, pea-shaped bone located on the palmar surface of the triquetrum.
Distal Row of Carpal Bones (lateral to medial):
● Trapezium: A four-sided bone on the lateral side of the wrist; it articulates with the 1st
and 2nd metacarpals, scaphoid, and trapezoid bones.
● Trapezoid: A wedge-shaped bone similar to the trapezium; it articulates with the 2nd
metacarpal, trapezium, capitate, and scaphoid.
● Capitate: The largest carpal bone, with a rounded head-like structure; it articulates
mainly with the 3rd metacarpal, as well as with the trapezoid, scaphoid, lunate, and
hamate.
● Hamate: A wedge-shaped bone on the medial side of the wrist, articulating with the 4th
and 5th metacarpals, capitate, and triquetrum. It features a prominent hook-like
projection, the hook of the hamate, which points anteriorly.
The proximal surfaces of the distal carpal bones articulate with the proximal row, and their
distal surfaces articulate with the metacarpals.
Metacarpus
The metacarpus forms the bony framework of the palm, lying between the carpus and the
phalanges. It consists of five metacarpal bones, each with a base (proximal), shaft, and
head (distal).
● The bases articulate with the carpals, and the heads articulate with the proximal
phalanges, forming the knuckles.
● The 1st metacarpal (thumb) is the shortest and thickest.
● The 3rd metacarpal is distinguished by a styloid process on the lateral side of its base.
Phalanges
Each finger (digit) has three phalanges—proximal, middle, and distal—except the thumb,
which has only two(proximal and distal).
● The phalanges of the thumb are broader and stronger than those of the other digits.
● Each phalanx consists of a base, a shaft, and a head.
● The proximal phalanges are the largest, the middle phalanges are intermediate, and
the distal phalanges are the smallest.
● The shafts taper toward the distal end, and the terminal phalanges are flattened and
expanded at their ends to support the nail beds.
