The
Ulna
The
Ulna so called from its forming the elbow is a long bone, prismatic in form, placed at the
inner side of the forearm, parallel with the radius. It is the larger and
longer of the two bones. Its upper extremity, of great thickness and
strength, forms a large part of the articulation of the elbowjoint; it diminishes in size
from above downward, its lower extremity being very small, and excluded from
the wrist-joint by the interposition of an interarticular fibro-cartilage. It
is divisible into a shaft and two extremities.
The
Upper Extremity, the strongest part of the bone, presents for examination two
large, curved processes, the Olecranon process and the Ooronoid process; and
two concave, articular cavities, the greater and lesser sigmoid cavities.
The
Olecranon Process is a large, thick, curved eminence situated at the upper
and back part of the ulna. It is curved forward at the summit so as to
present a prominent tip which is received into the olecranon fossa in
extension of the forearm; its base being contracted where it joins the shaft.
This is the narrowest part of the upper end of the ulna, and, consequently,
the most usual seat of fracture. The posterior surface of the
olecranon, directed backward. is triangular, smooth, subcutaneous, and covered by a bursa. Its
upper
rface
is of a quadrilateral form, marked behind by a rough impression for the
chment of the 'l'riceps muscle; and in front, near the margin, by a slight
trans-
~-
groove for the attachment of part of the posterior ligament of the
elbow-joint . . terior surface is smooth, concave, covered with cartilage in
the recent state, rms the upper and back part of the great sigmoid cavity.
The lateral present a continuation of the same groove that was seen on the
margin of - r surfaos , they serve for the attachment of ligaments; viz., the
back i ernal lateral
ligament internally, the posterior ligament externally. border is also
attached a part of the Flexor carpi ulnaris, while to the ._ attached the
Anconeus.
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