OSTEOLOGY. 



GENERAL ANATOMY OF THE SKELETON. 



THE general framework of the body is built up mainly of a series of bones, 

 supplemented, however, in certain regions by pieces of cartilage; the bony 

 part of the framework constitutes the skeleton. 



In comparative anatomy the term skeleton has a wider application, as in some 

 of the lower animals hard, protective, and supporting structures are more exten- 

 sively distributed, being developed in association with the integumentary system. 

 In such animals the skeleton may be described as consisting of an internal or 

 deep skeleton, the endoskeleton, and an external or superficial, the exoskeleton. 

 In the human subject the exoskeleton is extremely rudimentary, its only important 

 representatives being the teeth and nails. The term skeleton is, therefore, 

 confined to the endoskeleton, and this is divisible into an axial part, which includes 

 that of the head and trunk, and an appendicular part, which comprises that of 

 the limbs. 



In the skeleton of the adult there are 206 distinct bones, as follows: 



f Vertebral column 26 



Axial ) Skull 22 



Skeleton ^ Hyoid bone 1 



tllibs and sternum 25 



74 



Appendicular f Upper limbs 64 



Skeleton \ Lower limbs 62 



126 

 Auditory ossicles 6 



Total . . 206 



The patellae are included in this enumeration, but the smaller sesamoid bones 

 are not reckoned. 



Bones are divisible, according to their shape, into four classes long, short, 

 flat, and irregular. 



Long Bones. The long bones are found in the limbs, where they form a 

 system of levers, which sustain the weight of the trunk and confer the power of 

 locomotion and prehension. A long bone consists of a shaft and two extremities. 

 The shaft, or diaphysis, is a hollow cylinder, the central cavity being termed the 

 medullary canal; the wall consists of dense, compact tissue of considerable thickness 

 in the middle part of the shaft, but becoming thinner toward the extremities; 

 the cancellous tissue is scanty. The extremities, or epiphyses, are generally ex- 

 panded, for the purposes of articulation and to afford broad surfaces for muscle 

 attachment. They are usually developed from separate centres of ossification 

 termed epiphyses, and consist of cancellous tissue surrounded by a thin layer of 

 compact bone. The long bones are not straight, but curved, the curve generally 

 taking place in two planes, thus affording greater strength to the bone. The 



(35) 



