CHAPTER II 



THE SKELETAL SYSTEM 



THE SKELETON OF THE HORSE ' 



The skeleton may be divided for description into an axial 

 portion, consisting of the bones of the head and trunk, and an 

 appendicular portion, comprising the bones of the limbs (Frontis- 

 piece). The number of bones in the skeleton of an animal 

 varies with the age, owing to fusion of bones which are separate 

 in the young. There are 207 bones in the skeleton of the adult 

 horse. When dried the bones constitute from 7 to 8.5 per cent of 

 the body weight. 



The bones of vertebrates are embedded in the soft structures 

 of the body, f so are termed the endoskeleton. Many inverte- 

 brates have a skeleton placed outside the softer parts, as in the 

 case of the lobster's shell; such an arrangement is called an 

 exoskeleton. Occasionally a bone is found embedded in a soft 

 organ and does not articulate with the general skeleton; it be- 

 longs to the so-called splanchnic skeleton. The os cordis in the 

 ox's heart, os penis of the dog, and os rostri in the snout of the 

 hog are examples of bones belonging to the splanchnic skeleton. 



It is customary to classify the bones according to their shape. 

 The names, locations, and functions of the classes follow. 



Long bones have a marrow cavity and consist of a shaft and 

 two extremities. They are found exclusively in the limbs where 

 they serve as columns of support and act as levers, e.g., femur 

 or thigh bone. 



Flat bones are composed of two thin layers of compact substance 

 with a varying amount of cancellated substance between. They 

 serve to protect organs and to afford extensive surface for the 

 attachment of muscles, e.g., scapula or shoulder-blade. 



Short bones are cubical in form and occur chiefly in compound 

 joints where they aid in facilitating movement, e.g., the hock. 



Irregular bones are all single and lie along the median plane, 

 e.g., vertebrae. 



General terms used in the description of bones are defined 

 as follows: 



1 See Appendix for classified list of bones of the skeleton. 



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