CHAP. IV.] THE SKELETON. 25 



surface for muscular attachment. All long bones are more or 

 less curved, which gives them greater strength and a more 

 graceful outline. 



Short bones. The short bones are small pieces of bone 

 irregularly shaped. Their texture is spongy throughout, ex- 

 cepting at their surface, where there is a thin crust of compact 

 substance. 



Flat bones. Where the principal requirement is either exten- 

 sive protection or the provision of broad surfaces for muscular 

 attachment, the bony tissue expands into broad or elongated 

 flat plates. The flat bones are composed of two thin layers of 

 compact tissue, enclosing between them a variable quantity of 

 cancellous tissue. In the bones of the skull this outer layer 

 is thick and tough; the inner one, thinner, denser, and more 

 brittle. The cancellated tissue lying between the two layers, 

 or " tables of the skull," is called the diploe. 



Irregular bones. The irregular bones are those which, on 

 account of their peculiar shape, cannot be grouped under either 

 of the preceding heads. 



Bones of the upper extremity: 



Clavicle (collar bone) 2 



Scapula (shoulder blade) 2 



Humerus (arm) 2 



Ulna, 2 ) ,- 



_, , . r (forearm) 4 



Radius, 2 ) v 



Carpus (wrist) 16 



Metacarpus (palm of hand) 10 



Phalanges (fingers) 28 



64 



Thus enumerated we see that the bones of the upper extrem- 

 ity consist of the shoulder girdle (clavicle and scapula), of the 

 arm, the forearm, and the hand ; the bones of the hand being 

 further subdivided into those of the wrist, the palm of the hand, 

 and the fingers. 



The clavicle forms the anterior portion of the shoulder girdle. 

 It articulates by its inner extremity with the sternum, and by 

 its outer extremity with the acromion process 1 of the scapula. 



1 All eminences and projections of bones are termed processes, and these 

 processes were named by the early anatomists, either from their shape or use, 

 or from their fancied resemblance to some well-known object. It is well to look 



