170 PRACTICAL ANATOMY. 



two lines, an oblique and a vertical one, into three smaller surfaces. Above the 

 oblique line, which runs from the lesser sigmoid cavity to the posterior border of 

 the bone, is the anconeus muscle. To the oblique line the supinator brevis 

 muscle is attached. The surface below the oblique line is divided by a vertical 

 line into an internal and an external portion. 



What can you say of the portion of the posterior surface of the ulna internal 

 to the vertical line ? 



It gives origin to the extensor carpi ulnaris muscle. 



What can you say of the portion of the posterior surface of the ulna external 

 to the vertical line ? 



It gives attachment to the supinator brevis, the extensor ossis metacarpi pol- 

 licis, the extensor longus pollicis, and the extensor indicis muscles. 



Does t/ie head of the ulna enter into the formation of the wrist-joint f 



No ; the triangular fibro-cartilage intervenes. The head of the ulna articu- 

 lates with the sigmoid fossa in the lower end of the radius, forming the inferior 

 radio-ulnar articulation. 



The Humerus. (Fig. 129.) 



Locate, classify, and describe geometrically the humerus. 



It is the arm bone, located between the shoulder and elbow, and long by clas- 

 sification. It has an outer, an inner, and a posterior surface. It has an anterior, 

 an external, and an internal border. It has a superior extremity or upper one- 

 third ; an inferior extremity or lower one-third ; a middle one-third. 



Name the bony parts of the Jnimerus concerned in practical anatomy, and give 

 their practical importance. 



The head of the humerus articulates with the head of the scapula. 



The anatomical neck gives attachment to the capsule. 



The surgical neck is very often the seat of fracture. 



The bicipital groove lodges the long head of biceps muscle. 



The bicipital lips surmount and deepen the bicipital groove. 



The greater tuberosity gives tendinous insertion to three muscles. 



The lesser tuberosity gives tendinous insertion to one muscle. 



The internal condyle is developed by traction of flexors and pronators. 



The internal condylar ridge has the internal intermuscular septum. 



The external condyle is developed by extensors and supinators. 



The external condylar ridge has the external intermuscular septum. 



The capitellum articulates with the concave surface of the radius. 



The trochlea articulates with the greater sigmoid of the ulna. 



The coronoid fossa is produced mechanically by the coronoid process. 



The olecranon fossa is produced mechanically by the olecranon process. 



The radial depression is produced by the head of the radius. 



Name the muscles inserted into the greater tuberosity of the liumerus. 



The supraspinatus into the upper facet ; the infraspinatus into the middle 

 facet ; the teres minor into the lower facet. 



HOT.V is the lesser tuberosity occupied f 



By the tendinous insertion of the subscapularis muscle. It has one facet only. 



Where is the transverse hum era/ ligament and what is its function f 



It extends from the greater to the lesser tuberosity of the humerus, convert- 

 ing the bicipital groove into a canal for the lodgment of the long or scapular head 

 of the biceps muscle. 



Hoiv would you locate the surgical neck of the humerus f 



It is the constricted portion of the bone below the tuberosities. It is the 

 portion of the humerus most frequently fractured in the upper one-third. 



H&iv do the three fossa of the liumerus, in the vicinity of the elbow enhance the 

 gravity of a fracture passing through them f 



