CLASSES OF BONE. 43 



CHAPTER II. 



OSTEOLOGY. 



THE bones are the organs of support to the animal frame ; thty ive 

 firmness and strength to the entire fabric, afford points of connection to 

 the numerous muscles, and bestow individual character upon the body. 

 In the limbs they are hollow cylinders, admirably calculated by their con- 

 formation and structure to resist violence and support weight. In the 

 trunk and head, they are flattened and arched, to protect cavities and 

 provide an extensive surface for attachment. In some situations they 

 present projections of variable length, which serve as levers ; and in others 

 are grooved into smooth surfaces, which act as pulleys for the passage of 

 tendons. Moreover, besides supplying strength and solidity, they are 

 equally adapted, by their numerous divisions and mutual apposition, to 

 fulfil every movement which may tend to the preservation of the creature, 

 or be conducive to his welfare. 



According to the latest analysis by Berzelius, bone is composed of about 

 one-third of animal substance, which is almost completely reducible to 

 gelatine by boiling, and of two-thirds of earthy and alkaline salts. The 

 special constituents of bone are present in the following proportions : 



Cartilage 32-17 parts. 



Blood-vessels 1-13 



Phosphate of lime 51-04 



Carbonate of lime 11 '30 



Fluateoflime 2-00 



Phosphate of magnesia 1-16 



Soda, chloride of sodium 1-20 



100-00 



Bones are divisible into three classes: Long, flat, and irregular. 

 The Long bones are found principally in the limbs, and consist of a 

 shaft and two extremities. The shaft is cylindrical or prismoid in form, 

 dense and hard in texture, and hollowed in the interior into a medullary 

 canal. The extremities are broad and expanded, to articulate with ad- 

 joining bones ; and cellular or cancellous in internal structure. Upon the 

 exterior of the bone are processes and rough surfaces for the attachment 

 of muscles, and foramina for the transmission of vessels and nerves. The 

 character of long bones is, therefore, their general type of structure and 

 their divisibility into a central portion and extremities, and not so much 

 their length ; for there are some long bones, as the second phalanges of 

 the toes, which are less than a quarter of an inch in length, and almost 

 equal, and in some instances exceed, in breadth their longitudinal axis. 

 The long bones are, the clavicle, humerus, radius and ulna, femur, tibia 

 and fibula, metacarpal bones, metatarsal, phalanges, and ribs. 



Flat bones are composed of two layers of dense bone with an interme- 

 diate cellular structure, and are divisible into surfaces, borders, angles, and 

 processes. They are adapted to inclose cavities ; have processes upon 

 their surface for the attachment of muscles ; and are perforated by foramina, 

 for the passage of nutrient vessels to their cells, and for the transmission 



