DESCRIPTION OF THE SKELETON 145 



While the smooth or rounded forepart or body of 

 the vertebrae affords support to the superincumbent 

 parts, the projecting ridge behind, and rugged pro- 

 cesses at the sides, combine with it to form a large 

 tube or canal, extending from the top to the bottom 

 of the column in which the spinal marrow is con- 

 tained and protected. Between each of the verte- 

 brae a thick compressible cushion of cartilage and 

 ligament is interposed, which serves the triple pur- 

 pose of uniting the bones to each other, of dimin- 

 ishing and diffusing the shock in walking or leaping, 

 and of admitting a greater extent of motion than if 

 the bones were in more immediate contact. 



The ribs rr, twelve in number on each side, are 

 attached by their heads to the spine, and by their 

 other (cartilaginous) extremities to the sternum or 

 breast-bone x. The seven uppermost are called true 

 ribs, because each of them is connected directly with 

 the sternum, by means of a separate cartilage. The 

 five lower ribs are called false, because one or two 

 of them are loose at one end, and the cartilages of 

 the rest run into each other instead of being sepa- 

 rately prolonged to the breast-bone. The use of 

 the ribs is to form the cavity of the chest for the re- 

 ception and protection of the lungs, heart, and great 

 blood-vessels, and to assist in respiration by their 

 alternate rising and falling. This action enlarges 

 and diminishes the size of the chest and the capa- 

 city of the lungs. 



The pelvis s s is formed by the broad flat bones 

 which support the bowels and serve for the articu- 

 lation of the thigh. A general notion of their ap- 

 pearance and uses may be obtained from inspection 

 of the cut, which, however, does not with perfect 

 accuracy represent the more minute structure. 



The bones of the upper extremities are, the scapula 



or shoulder-blade ; the clavicle or collar-bone y ; the 



kumerus or arm-bone I ; the radius d, and ulna e, or 



bones of the forearm ; and the small carpal and meta- 



N 



