182 SPECIAL ANATOMY OF THE SKELETON 



Triceps, the former of which is attached to its upper and outer part, the latter to 

 its inner and back part, the two being separated by the musculospiral groove. 

 The Lower or Distal Extremity is flattened from before backward, and curved 

 slightly forward; it terminates below in a broad, articular surface which is divided 

 into two parts by a slight ridge. Projecting on either side are the external and 

 internal condyles. By some anatomists the external condyle is called the external 

 epicondyle and the internal condyle is called the internal epicondyle. The articular 

 surface extends a little lower than the condyles, and is curved slightly forward, so 

 as to occupy the more anterior part of the bone; its greatest breadth is in the 

 transverse diameter, and it is obliquely directed, so that its inner extremity occupies 

 a lower level than the outer. The outer portion of the articular surface presents 

 a smooth, rounded eminence, which has received the name of the capitellum, or 

 radial head of the humerus (capitulum humeri) ; it articulates w r ith the cup-shaped 

 depression on the head of the radius, and is limited to the front and lower part of 

 the bone, not extending as far back as the other portion of the articular surface. 

 On the inner side of this eminence is a shallow groove, in which is received the 

 inner margin of the head of the radius. Above the front part of the capitellum 

 is a slight depression, the radial fossa (fossa radians'), which receives the anterior 

 border of the head of the radius when the forearm is flexed. The inner portion 

 of the articular surface, the trochlea (trochlea humeri), presents a deep depression 

 between two well-marked borders. This surface is convex from before backward, 

 concave from side to side, and occupies the anterior, lower, and posterior parts 

 of the bone. The external border, less prominent than the internal, corresponds 

 to the interval between the radius and the ulna. The internal border is thicker, 

 more prominent, and consequently of greater length, than the external. The 

 grooved portion of the articular surface fits accurately within the greater sigmoid 

 cavity of the ulna; it is broader and deeper on the posterior than on the anterior 

 aspect of the bone, and is inclined obliquely from behind forward and from without 

 inward. Above the front part of the trochlear surface is seen a smaller depression, 

 the coronoid fossa (fossa coronoidea), which receives the coronoid process of the 

 ulna during flexion of the forearm. Above the back part of the trochlear surface 

 is a deep, triangular depression, the olecranon fossa (fossa olecrani), in which 

 is received the summit of the olecranon process in extension of the forearm. 

 These fossae are separated from one another by a thin, transparent lamina of bone, 

 which is sometimes perforated by a foramen, the supratrochlear foramen; their 

 upper margins afford attachment to the anterior and posterior ligaments of the 

 elbow-joint, and they are lined, in the recent state, by the synovial membrane 

 of this articulation. The articular surfaces, in the recent state, are covered with 

 a thin layer of hyaline cartilage. The external condyle (epicondylus lateral is) 

 is a small, tubercular eminence, less prominent than the internal, curved a little 

 forward, and giving attachment to the external lateral ligament of the elbow- 

 joint, and to a tendon common to the origin of some of the Extensor and Supinator 

 muscles. The internal^pndjle_(>g^roc^/ea or epicondylus medialis), larger and 

 more prominentTls^^irected a little backward; it gives attachment to the internal 

 lateral ligament, to the Pronator teres, and to a tendon common to the origin of 

 some of the Flexor muscles of the forearm. The ulnar nerve runs in a groove, 

 the ulnar groove (sulcus nervi ulnaris), at the back of the internal condyle, or 

 between it and the olecranon process. These condyles are directly continuous 

 above with the external and internal supracondylar ridges. 



Structure. The extremities consist of canceUous tissue, covered with a thin compact layer; 

 the shaft is composed of a cylinder of compact tissue, thicker at the centre than at the extremities, 

 and hollowed out by a large medullary canal, which extends along its whole length. In the 

 head of the humerus the plates of the cancellous tissue are arranged in curves (Fig. 143), 

 known as pressure curves. Most of the bone plates are at right angles to the plane of the 



