THE HUMAN SKELETON. 86 



ity of the sternum. In old people, this cartilage is often 

 changed into bone. 



41. The manner in which the ribs are attached to the 

 sternum by means of slips of elastic cartilage, is worthy of 

 particular notice, fit is to this circumstance that it is 

 owing, that the ribs are so seldom injured by blows and falls ; 

 for if they were wholly bone from one extremity to the other, 

 life would be endangered by any accidental fracture, and 

 even the rubs and jolts to which we are continually exposed, 

 would be too much for their delicate and brittle texture. 

 When we lean forward or to one side, the ribs accommodate 

 themselves not by a change of form in the bones, but by the 

 bending of the cartilages. It is owing to this elasticity that 

 the blows of boxers so seldom succeed in fracturing the ribs ; 

 as they yield in proportion to the violence of the force in- 

 flicted. But this is not the case in old age. Then the car- 

 tilages of the ribs become bony, and the whole arch unyield- 

 ing and inelastic ; so that blows which formerly would have 

 caused little or no injury, are now attended with fracture of 

 the rib. The influence of the elastic structure of the ribs, 

 in the action of breathing, is highly interesting and import- 

 ant, and will be fully explained when we come to treat of 

 Respiration. < 



42. (The next division of the trunk is called the pelvis or 

 fom'n, 1 which{consists of a circle of large firm bones, situated 

 between the lower portion of the trunk and the inferior 

 extremities? They are the sacrum, the coccyx, the ilium, the 

 ischium, and the pubis. The ilium forms the upper, the 

 ischium the lower, while the pubis is situated at the fore part 

 of the pelvis ; and each one of these bones contributes to 

 form the large and deep socket, for the head of the thigh 

 bone. {The pelvis not only affords lodgment for the organs 

 contained within its cavity, but it also sustains the entire 

 weight of the body, and furnishes sockets for the heads of the 

 thigh bones to roll in, and a broad surface for numerous mus- 

 cles to spring from, 



8 



