THE SKELETON. 
55 
lar surface of the distal extremity consists of the capitellum, 
for articulation with the head of the radius, and the trochlea 
for articulation with the sigmoid cavity 
of the ulna. On the cranial side of the 
proximal third of the bone is the rough 
deltoid ridge for the insertion of the 
deltoid muscle which arises from the 
shoulder girdle. 
The ulna is the longest bone of the 
forearm or antebrachium, and is caudad 
of the radius. It articulates in the greater 
sigmoid cavity with the trochlea of the 
humerus and in the lesser sigmoid cavity 
with the head of the radius. The distal 
articulation is with the radius, cuneiform 
and pisiform (Fig. 21). The olecranon 
process forms the proximal termination 
of the bone and serves for the insertion 
of the triceps muscle. Distad of the sig- 
moid cavity is a projection known as the 
coronoid process. The styloid process 
forms a small projection on the distal 
extremity of the bone. 
The radius is the preaxial or cranial 
bone of the antebrachium. It articulates 
proximally with the capitellum of the 
humerus and the lesser sigmoid cavity 
of the ulna, and distally with the scapho- 
lunar and ulna. It bears but two proc- 
esses, the tubercle and the styloid process. 
The tubercle (Fig. 34) is a slight knot 
near the proximal end on the ulnar side. 
Fic. 33. LATERAL 
or Outer As- 
PECT OF THE 
Ricut ULna. 
ar, Articular facet 
for radius; cr, 
coronoid  proc- 
ess; gs, greater 
sigmoid cavity; 
/s, lesser sigmoid 
cavity; on, ole- 
cranon process; 
st, styloid proc- 
ess. 
Proximal from the tubercle is the neck which supports the 
head bearing a concave crown for articulation with the 
