The Ulna of the body

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 upperrface 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.