_a_, head; _b_, greater tuberosity; _c_, lesser tuberosity; _d_,
bicipital groove; _e_, pectoral ridge; _f_, deltoid ridge; _g_, rough
area for insertion of latissimus dorsi and teres major; _h_, nutrient
foramen; _i_, capitulum; _j_, trochlea; _l_, coronoid fossa; _m_,
radial fossa; _n_, medial epicondyle; _o_, lateral epicondyle; _q_,
supracondyloid foramen.]
Along the lateral border of the proximal end of the shaft is a high
rough ridge semicircular in side view, the =great tuberosity= (_b_). It
gives attachment to muscles and is marked on its dorsal border by a deep
depression for the tendon of the infraspinatus muscle. On the medial
margin of the proximal end closely associated with the head is a smaller
elevation, the =lesser tuberosity= (_c_), also for muscular attachment.
Between the greater and lesser tuberosities on the ventral surface is
seen a broad groove, the =sulcus intertubercularis= or =bicipital
groove= (_d_), which passes distad onto the surface of the shaft. In the
natural state it is converted into a canal by overlying tendons and
lodges the tendon of the biceps muscle.
The shaft is nearly cylindrical at its middle, but its dorsoventral
diameter is slightly greater than its mediolateral diameter. Its
proximal end is flattened mediolaterad, while its distal end is
flattened dorsoventrad.
From the ventral margin of the greater tuberosity a ridge, the
=pectoral= ridge (_e_), is continued onto the surface of the shaft, and
from the dorsal margin another ridge, the =deltoid= ridge (_f_), passes
distad and ventrad so as to meet the pectoral ridge near the middle of
the ventral surface of the bone. On the medial margin of the bone near
the junction of the first and second fourths is a roughened area (_g_)
for the attachment of the tendons of the latissimus dorsi and teres
major muscles, and on the same surface near the junction of the second
and last thirds is a nutrient foramen (_h_).
The distal end of the bone presents a smooth saddle-shaped articular
surface, which, in well-marked bones, is divided, when seen from the
ventral surface, by a slight nearly median ridge into two unequal
portions, lateral and medial (_i_ and _j_). The lateral half is rounded
and is called the =capitulum= (_i_). It is broader ventrad than dorsad,
and is not continued onto the dorsal surface of the bone. It is for
articulation with the proximal end of the radius.
The medial half of the surface, the =trochlea= (_j_), is concave and
passes directly into the capitular surface laterad, but is limited
mediad by a sharp ridge. It is continued onto the dorsal surface of the
bone, where it is limited also laterad by a ridge. It articulates with
the semilunar notch of the ulna.
Proximad of the trochlea the dorsal surface presents a deep fossa, the
=olecranon fossa=, which receives the olecranon of the ulna when the arm
is straightened. On the ventral surface (Fig. 47) are two shallower
fossæ separated by a longitudinal ridge. The one over the trochlea
receives the coronoid process of the ulna when the arm is bent, and is
called thence the =coronoid fossa= (_l_). The one over the capitulum,
the =radial fossa= (_m_), receives a triangular facet on the proximal
end of the radius at the same time. Between the radial and coronoid
fossæ on one side and the olecranon fossa on the other is only a thin
plate of bone. On the medial surface of the distal end is a considerable
roughened elevation, the =medial epicondyle= (_n_) (epitrochlea). It
gives origin to flexor muscles and to the ulnar collateral ligaments of
the elbow-joint. Opposite the medial epicondyle over the capitulum is
the =lateral epicondyle= (_o_) for the origin of extensor muscles of the
forearm and of the radial collateral ligaments of the elbow-joint. From
the lateral epicondyle a ridge, the lateral =supracondyloid ridge=
(_p_), continues proximad, curving onto the dorsal surface of the bone
and ending about opposite the junction of the deltoid and pectoral
ridges.
Proximad of the medial epicondyle the bone is pierced near its medial
margin by an oblique oval foramen, the =supracondyloid foramen= (_q_).
=Radius= (_I_, Figs. 49 and 50).--In the usual position the radius lies
with its proximal end on the lateral side of the arm, articulating with
the capitulum of the humerus. The proximal end is thus laterad of the
proximal end of the ulna. Its distal end, however, lies on the medial
side of the distal end of the ulna, so that the radius in the natural
position crosses ventrad of the ulna.
The radius is a curved bone slightly flattened dorsoventrally, with
enlarged ends. It may be described as consisting of a shaft and of a
proximal and a distal end. Its proximal end presents on the ventral
surface a tuberosity, the =bicipital tuberosity= (_c_), for the
insertion of the tendon of the biceps muscle. Proximad of this the bone
is contracted to form a =neck= (_b_) which is surmounted by a =head=
(_a_). The head has on its proximal surface a depressed oval facet by
which it articulates with the capitulum, and on its ulnar border a long
narrow facet, the =articular circumference= (_d_), for articulation with
the radial notch of the ulna; also a triangular facet (_e_), which fits
into the radial fossa of the humerus.
The shaft is convex dorsad and concave ventrad. The distal end is
somewhat pyramidal. From its medial or radial side a wedge-shaped
process, the =styloid= process (_f_), extends distad. The distal
surface of the end together with the lateral surface of the styloid
process form a concave articular cavity (_g_) which fits against the
scapholunar bone.
[Illustration: FIG. 49.--RADIUS AND ULNA, DORSOLATERAL VIEW.