osteology and myology of ulna bone

1. Ulna Bone
Dr. Sami

2. 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 forearm as the little finger.
It runs parallel to the radius, the other long bone in the forearm.
The ulna is usually slightly longer than the radius, but the radius is thicker.
Therefore, the radius is considered to be the larger of the two.

3. Proximal End:
 Near the elbow,
 the ulna has two curved processes,
 the olecranon and the coronoid process;
 two concave, articular cavities,
 the semilunar and radial notches.

6.  The olecranon is a large, thick, curved eminence, situated at the upper and
back part of the ulna.
 It is bent forward at the summit so as to present a prominent lip which is
received into the olecranon fossa of the humerus in extension of the forearm.
 Its base is contracted where it joins the body and the narrowest part of the
upper end of the ulna.
 Its posterior surface, directed backward, is triangular, smooth, subcutaneous,
and covered by a bursa.
 Its superior surface is of quadrilateral form, marked behind by a rough
impression for the insertion of the triceps brachii;
 and in front, near the margin, by a slight transverse groove for the attachment
of part of the posterior ligament of the elbow joint.

7.  Its anterior surface is smooth, concave, and forms the upper part of the
semilunar notch.
 Its borders present continuations of the groove on the margin of the superior
surface;
 they serve for the attachment of ligaments: the back part of the ulnar
collateral ligament medially, and the posterior ligament laterally.
 From the medial border a part of the flexor carpi ulnaris arises; while to the
lateral border the anconeus is attached.

10. coronoid process
 The coronoid process is a triangular eminence projecting forward from the
upper and front part of the ulna.
 Its base is continuous with the body of the bone, and of considerable
strength.
 Its apex is pointed, slightly curved upward, and in flexion of the forearm is
received into the coronoid fossa of the humerus.
 Its upper surface is smooth, concave, and forms the lower part of the
semilunar notch.
 Its antero-inferior surface is concave, and marked by a rough impression for
the insertion of the brachialis.

11.  At the junction of this surface with the front of the body is a rough eminence,
the tuberosity of the ulna, which gives insertion to a part of the brachialis; to
the lateral border of this tuberosity the oblique cord is attached.
 Its lateral surface presents a narrow, oblong, articular depression, the radial
notch.
 Its medial surface, by its prominent, free margin, serves for the attachment
of part of the ulnar collateral ligament.

12.  At the front part of this surface is a small rounded eminence for the origin of
one head of the flexor digitorum superficialis;
 behind the eminence is a depression for part of the origin of the flexor
digitorum profundus;
 descending from the eminence is a ridge which gives origin to one head of the
pronator teres.
 Frequently, the flexor pollicis longus arises from the lower part of the
coronoid process by a rounded bundle of muscular fibers.

13. semilunar notch
 The semilunar notch is a large depression, formed by the olecranon and the
coronoid process, and serving as articulation with the trochlea of the
humerus.
 About the middle of either side of this notch is an indentation, which
contracts it somewhat, and indicates the junction of the olecranon and the
coronoid process.
 The notch is concave from above downward, and divided into a medial and a
lateral portion by a smooth ridge running from the summit of the olecranon to
the tip of the coronoid process.
 The medial portion is the larger, and is slightly concave transversely; the
lateral is convex above, slightly concave below.

14. radial notch
 The radial notch is a narrow, oblong, articular depression on the lateral side
of the coronoid process;
 it receives the circumferential articular surface of the head of the radius.
 It is concave from before backward, and its prominent extremities serve for
the attachment of the annular ligament.

15. Distal End
 The head of ulna presents an articular surface, part of which, of an oval or
semilunar form, is directed downward, and articulates with the upper surface
of the triangular articular disc which separates it from the wrist-joint; the
remaining portion, directed lateralward, is narrow, convex, and received into
the ulnar notch of the radius.
 Near the wrist, the ulnar, with two eminences; the lateral and larger is a
rounded, articular eminence, termed the head of the ulna; the medial,
narrower and more projecting, is a non-articular eminence, the styloid
process.

16.  The head presents an articular surface, part of which, of an oval or semilunar
form, is directed downward, and articulates with the upper surface of the
triangular articular disk which separates it from the wrist-joint; the remaining
portion, directed lateralward, is narrow, convex, and received into the ulnar
notch of the radius.
 The styloid process projects from the medial and back part of the bone; it
descends a little lower than the head, and its rounded end affords
attachment to the ulnar collateral ligament of the wrist-joint.
 The head is separated from the styloid process by a depression for the
attachment of the apex of the triangular articular disk, and behind, by a
shallow groove for the tendon of the extensor carpi ulnaris.

17. Body
 The body of the ulna at its upper part is prismatic in form, and curved so as
to be convex behind and lateralward; its central part is straight; its lower
part is rounded, smooth, and bent a little lateralward.
 It tapers gradually from above downward, and has three borders and three
surfaces.

18. Borders
 The volar border (margo volaris; anterior border) begins above at the
prominent medial angle of the coronoid process, and ends below in front of
the styloid process.
 Its upper part, well-defined, and its middle portion, smooth and rounded,
give origin to the flexor digitorum profundus;
 its lower fourth serves for the origin of the pronator quadratus. T
 his border separates the volar from the medial surface.

19.  The dorsal border (margo dorsalis; posterior border) begins above at the apex
of the triangular subcutaneous surface at the back part of the olecranon, and
ends below at the back of the styloid process;
 it is well-marked in the upper three-fourths, and gives attachment to an
aponeurosis which affords a common origin to the flexor carpi ulnaris, the
extensor carpi ulnaris, and the flexor digitorum profundus;
 its lower fourth is smooth and rounded.
 This border separates the medial from the dorsal surface.

20.  The interosseous crest (crista interossea; external or interosseous border)
begins above by the union of two lines, which converge from the extremities
of the radial notch and enclose between them a triangular space for the
origin of part of the Supinator;
 it ends below at the head of the ulna.
 Its upper part is sharp, its lower fourth smooth and rounded.
 This crest gives attachment to the interosseous membrane, and separates the
volar from the dorsal surface.

21. Surfaces
 The volar surface (facies volaris; anterior surface), much broader above
than below, is concave in its upper three-fourths, and gives origin to the
flexor digitorum profundus;
 its lower fourth, also concave, is covered by the pronator quadratus.
 The lower fourth is separated from the remaining portion by a ridge, directed
obliquely downward and medialward, which marks the extent of origin of the
pronator quadratus.
 At the junction of the upper with the middle third of the bone is the nutrient
canal, directed obliquely upward.

22.  The dorsal surface (facies dorsalis; posterior surface) directed backward
and lateralward, is broad and concave above; convex and somewhat narrower
in the middle; narrow, smooth, and rounded below.
 On its upper part is an oblique ridge, which runs from the dorsal end of the
radial notch, downward to the dorsal border; the triangular surface above this
ridge receives the insertion of the Anconæus, while the upper part of the
ridge affords attachment to the supinator.
 Below this the surface is subdivided by a longitudinal ridge, sometimes called
the perpendicular line, into two parts: the medial part is smooth, and
covered by the extensor carpi ulnaris; the lateral portion, wider and rougher,
gives origin from above downward to the Supinator, the abductor pollicis
longus, the extensor pollicis longus, and the extensor indicis proprius.

23.  The medial surface (facies medialis; internal surface) is broad and concave
above, narrow and convex below.
 Its upper three-fourths give origin to the Flexor digitorum profundus; its lower
fourth is subcutaneous.