CHAPTER VI 

 THE PHYSIOLOGY OF THE SKELETON 



The skeleton in its entirety determines the plan of organization of the 

 animal body and imparts to it its characteristic features. In its entirety it 

 serves for the attachment of muscks, the support of viscera and by reason of 

 the relation of the bones one to another, permits of a great variety of move- 

 ments. The skeleton may be divided into an axial and an appendicular 

 portion. 



The Axial Portion. The axial portion consists of the bones of the head, 

 of the vetebral column and the ribs. The vertebral column is the foundation 

 element and the center around which the appendicular portions are de- 

 veloped and arranged with a certain degree of conformity. It is composed 

 of a series of superimposed bones, the vertebrae; which increase in size from 

 above downward as far as the brim of the pelvic cavity. Superiorly, it 

 supports the skull; laterally, it affords attachment for the ribs, which in 

 turn support the weight of the upper extremities; below, it rests upon the 

 pelvic bones, which transmit the weight of the body to the inferior extremities. 

 The bodies of the vertebrae are united one to another by tough elastic discs 

 of fibro-cartilage, which, collectively, constitute about one-quarter of the 

 length of the vertebral column. The vertebrae are held together by ligaments 

 situated on the anterior and posterior surfaces of their bodies, and by short, 

 elastic ligaments between the neural arches and processes. These structures 

 combine to render the vertebral column elastic and flexible, and enable it to 

 resist and diminish the force of shocks communicated to it. In all the static 

 and dynamic states of the body it plays a most essential r61e. The character 

 and the arrangement of the bones of the axial portion endow the animal 

 mechanism with a certain degree of fixity combined with slight mobility. 



The Appendicular Portion. The appendicular portion consists 

 of the bones of the arms and legs, the scapular and pelvic arches. By 

 reason of its character and anatomic arrangement, the animal body is en- 

 dowed with extreme mobility, enabling the animal to execute a great variety 

 of rapid and extensive movements which, however, vary in degree in different 

 animals in accordance with their organization and the nature of their 

 environment. 



For the manifestation of the activities of the animal it is essential that the 

 relation of the various portions of the bony skeleton to one another shall be 

 such as to permit of movement while yet retaining close apposition. This 

 is accomplished by the mechanical conditions which have been evolved at 

 the points of union of bones, and which are technically known as articulations 

 or joints. 



A consideration of the body movements involves an account of (i) the 

 static conditions, or those states of equilibrium in which the body is at rest 

 e.g., standing, sitting; (2) the dynamic conditions, or those states of 

 activity characterized by movement e.g., walking, running, etc. In this 

 connection, however, only those physical and physiologic peculiarities of the 



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