48 



ANATOMY. 



Describe the Radius. The radius lies externally to the ulna when the 

 fore-arm is in supination ; it is prismatic in form with the base below where it 

 articulates with the carpus. The bone is curved outwards and is shorter than 

 the ulna, by the length of the olecranon. It presents the following points from 

 above downwards, viz. 



Head,k cylindrical and cup-shaped, articulating with the radial head of the 

 humerus, and the lesser sigmoid cavity of the ulna, and playing within 

 the orbicular ligament. 



Neck,l the constricted part below the head. 



Tuberosity, rough behind for the insertion of the biceps, and smooth in 

 front where it is covered by a bursa. 



Shaft,j prismoid in form, presents a sharp border internally for the attach- 

 ment of the interosseous membrane; the Nutrient Foramen is on its an- 

 terior surface. It gives attachment to 8 of the 12 muscles of the fore-arm. 



Sigmoid Cavity, at the internal side of the carpal end, is shallow, and artic- 

 ulates with the head of the ulna. 



Articular Surface j> is divided by a ridge into 2 facets for articulation with 

 the semilunar and scaphoid bones of the carpus. 



Styloid Process, P externally, gives attachment by its apex to the external 

 lateral ligament, and by its base to the supinator longus muscle. 



Grooves, on the posterior and external surfaces of the lower extremity, for 

 the tendons of the 8 extensor muscles of the thumb, and those of the 

 radial side of the wrist, and fingers. 



THE HAND. 



How are the Bones of the Hand divided ? Into the carpus (8), the meta- 



FIG. 25. 



carpus (5), and the phalanges (14). Total, 

 27 bones. 



Name the Bones of the Carpus. They 

 are placed in 2 rows, one row in front of the 

 other, with 4 bones in each row, as follows, 

 the left hand being in supination, naming 

 from without inwards, viz. 



ist, or Proximal Row, Scaphoid^ Semi- 

 lunar,^ Cuneiform, C Pisiform. P 



2d, or Distal Row, Trapezium, T Trape- 

 zoid,^ Os -magnum, -^ Unciform.^ 



State the number of Articulations in the 

 Carpus. 34, as follows, the number after 

 each bone representing the number of its 

 articulations, viz. 



