CARPUS. 69 T 



smooth, and covered with cartilage, called the greater sig- 

 moid cavity, which receives the trochlea of the humerus. 

 This cavity is divided by a vertical ridge, and about its 

 centre by a transverse ridge, which terminates internally 

 in a notch, in which fatty matter is found. 



The inferior or carpal extremity is small, and presents a 

 projecting process, called the styloid, to which the internal 

 lateral ligament of the wrist is attached. External to 

 this process is a round smooth head for articulating with 

 the small cavity on the inner side of the radius; and 

 between these two processes, on the back of the ulna, is a 

 groove for the passage of the tendon of the extensor carpi 

 ulnaris. 



Structure. Same as the radius. Like that bone, it is 

 developed from three points of ossification. Ossification 

 begins in the ulna during the sixth week, shortly after it 

 takes place in the radius and humerus. At birth both 

 extremities are cartilaginous. The lower end has in its 

 centre an ossific point about the fourth or fifth year. The 

 olecranon is ossified from the seventh to the tenth, and 

 the bone is completed about the twentieth year. It is 

 articulated to the humerus and radius. 



SECTION IV. 

 THE HAND. 



The Hand is composed of the carpus, metacarpus, and 

 phalanges. 



THE CARPUS OR WRIST, (Fig. 219.) 



The carpus consists of two rows of bones, eight in 

 number. The first row contains the os scaphoides, lunare, 

 cuneiforme, and pisiforme, which are adjacent to the bones 

 of the forearm. The second row is next to the metacarpus, 

 and contains the trapezium, trapezoides, magnum and 

 unciforme. 



The 05 scai^lioides, (os naviculare,) so called from its fan- 

 cied resemblance to a boat, is situated upon the radial side, 

 and is the largest bone in the upper row. Its upper sur- 



