THE BONES. 



31 



some weeks, the cartilage is found to have lost its cohesion and its 

 smooth surface, and appears exactly as if the bone had been covered 

 with white velvet. It is seen to consist of an infinity of fibres 

 set perpendicularly on the surface of the bone, so that when pres- 

 sure is made on their ends, they yield by bending a little sideways, 

 but are prevented from yielding much, by the closeness with which 

 they are set together. In effect, the result is just what is seen on a 

 larger scale, if the finger is pressed against the surface of a common 

 flat cloth brush, the bristles bending a little sideways, and so pre- 

 senting an indentation on the surface. 



The account which has now been given of the nature of bones, as 

 a tissue, is applicable not only to those of man, but of all the other 

 mammalia, and of birds. In the arrangement of. the bones, how- 

 ever, every species differs from the rest, according to the purposes 

 which its body and limbs are to serve. The bones united in their 

 places constitute the skeleton. 



The SKELETON consists of the head, trunk, and extremities. The 

 trunk is composed of the spine, the ribs, the sternum or breast-bone, 

 and the pelvis, supporting the head upon its upper end, and resting 

 its lower end on the heads of the thigh-bones. The extremities are 

 four, two superior, commonly called in man the arms, two inferior, 

 commonly called the legs ; but in strict anatomical language, the 

 word leg is applied only to the part below the knee, the part above 

 being always spoken of as the thigh ; and the part above the elbow 

 only is called the arm, the part below the elbow being the forearm. 

 We will now examine these parts in succession more minutely. 



The spine is the central column, resting on the pelvis and thigh 

 bones, and supporting the chest, the head, and the superior ex- 

 tremities. It is about one third of the length of the whole body, 

 so that in a man who stands six feet high, the spine will be found, 

 about two feet long. It consists of twenty-four pieces or vertebra?, 

 named from the Latin word vertere, to turn, on account of their 

 mobility. The largest is placed below, and they diminish gra- 

 dually to near the top. Each vertebra is a mixed bone in its 

 structure, and has a body and processes; the word process in 

 anatomy signifying a projection or prominence. The body of each 

 vertebra is of the nature of a short bone, spongy in its texture, and 

 very light. It is semicircular, or nearly so, flat above and below, 

 where it supports and rests upon its neighbors. In the accompany- 

 ing cut, B represents the body of the vertebra with its flat surface 



