212 THE SKELETON. 



Major ; to the posterior bicipital ridge and groove, the Latissimus Dorsi and 

 Teres Major; to the shaft, the Deltoid, Coraco-brachialis, Brachialis Anticus, 

 external and internal heads of the Triceps ; to the internal condyle, the Pro- 

 nator Kadii Teres, and common tendon of the Flexor Carpi Radialis, Palmaris 

 Longus, Flexor Digitorum Sublimis, and Flexor Carpi Ulnaris ; to the external 

 condyloid ridge, the Supinator Longus, and Extensor Carpi Radialis Longior; 

 to the external condyle, the common tendon of the Extensor Carpi Radialis 

 Brevior, Extensor Communis Digitorum, Extensor Minimi Digiti, and Extensor 

 Carpi Ulnaris, the Anconeus, and Supinator Brevis. 



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

 the elbow and wrist. It is composed of two bones, the Ulna and the Radius. 



THE ULXA. 



The Ulna (Figs. 157, 158), so called from its forming the elbow (wJu'n/), 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 npper 

 extremity, of great thickness and strength, forms a large part of the articula- 

 tion of the elbow-joint; it diminishes in size from above downwards, its lower 

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

 tion of an interarticular fibre-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 coronoid process ; and 

 two concave articular cavities, the greater and lesser sigmoid cavities. 



The olecranon process (wx*^, elbow ; xpa.vov, head) is a large thick curved emi- 

 nence, situated at the upper and back part of the ulna. It rises somewhat 

 higher than the coronoid, and is curved forward at the summit so as to present 

 a prominent tip, 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 backwards, is 

 of a triangular form, smooth, subcutaneous, and covered by a bursa. Its upper 

 surface, directed upwards, 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, coverec. 

 with cartilage in the recent state, and forms the upper and back part of tho 

 great 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. The olecranon process, in its 

 structure as well as in its position and use, resembles the patella in the lower 

 limb ; and, like it, sometimes exists as a separate piece, not united to the rest 

 of the bone. 1 



The coronoid process (xopo^, a croio's beak) is a rough triangular eminence of 

 bone which projects horizontally forwards from the upper and front part of tho 

 ulna, forming the lower part of the great sigmoid cavity. 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 upwards, and 

 received into the coronoid depression of the humerus in flexion of the forearm. 

 Its upper surface is smooth, concave, and forms the lower part of the great 

 sigmoid cavity. The under surface is concave, and marked internally by a 

 rough impression for the insertion of the Brachialis Anticus. At the junction 



' Professor Owen regards the olecranon as homologous not with the patella, but with au 

 extension of the upper end of the fibula above tin- knee-joint, which is met with in the Omi- 

 thorynchus, Echidna, and some other animals. (OwKN, "On the Xalure of Limbs.") 



