THE ULNA, OR ELBOW BONE 185 



utility of the limb. They include the T-shaped fracture and oblique fractures which involve 

 the articular surface. The fractures which do not involve the joint are the transverse above 

 the condyles and the so-called epitrochlear fracture, in which the tip of the internal condyle 

 is broken off, generally by direct violence. 



Under the head of separation of t fie lower epipht/sis two separate injuries have been described: 

 (1) Where the whole of the four ossific centres which form the lower extremity of the bone 

 are separated from the shaft; and (2) where the articular portion is alone separated, the two 

 condvles remaining attached to the shaft of the bone. The epiphyseal line between the shaft 

 and lower end runs across the bone just above the tips of the condyles, a point to be borne in 

 mind in performing the operation of excision. Shortening may follow epiphysitis. 



Tumors originating from the humerus are of frequent occurrence. A not uncommon place 

 for a chondroma to grow from is the shaft of the bone somewhere in the neighborhood of the 

 insertion of the deltoid. Sarcomata frequently grow from this bone. 



THE FOREARM. 



The forearm is that portion of the upper extremity which is situated between 

 the elbow and the wrist. Its skeleton is composed of two bones, the ulna and 

 radius. 



The Ulna, or Elbow Bone (Figs. 145, 147). 



The ulna 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 elbow-joint; it diminishes in size from above downward, its 

 lower extremity being very small, and excluded from the wrist-joint by the inter- 

 position of an intra-articular fibrocartilage. It is divisible into a shaft and two 

 extremities. 



The Upper or Proximal Extremity, the strongest part of the bone, presents 

 for examination two large, curved processes, the olecranon process and the 

 coronoid process; and two concave, articular cavities, the greater and lesser 

 sigmoid cavities. 



The olecranon process (olecranon^ 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 of the 

 humerus 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. The posterior 

 surface of the olecranon, directed backward, is triangular, smooth, subcutaneous, 

 and covered by a bursa. Its upper surface is of a quadrilateral form, marked 

 behind by a rough impression for the attachment of the Triceps muscle; and in 

 front, near the margin, by a slight transverse groove for the attachment of part 

 of the posterior ligament of the elbow-joint. Its anterior surface is smooth, 

 concave, covered with cartilage in the recent state, and forms the upper and 

 back part of the greater sigmoid cavity. The lateral borders present a continuation 

 of the same groove that was seen on the margin of the superior surface; they serve 

 for the attachment of ligaments viz., the back part of the internal lateral ligament 

 internally, the posterior ligament externally. To the inner border is also attached 

 a part of the Flexor carpi ulnaris, while to the outer border is attached the Anconeus 

 muscle. 



The coronoid process (processus coronoideus] is a triangular eminence of bone 

 which projects horizontally forward from the upper and front part of the ulna. 

 Its base is continuous with the shaft, and of considerable strength; so much so 

 that fracture of it is an accident of rare occurrence. Its apex is pointed, slightly 

 curved upward, and is received into the coronoid depression of the humerus in 



