XXXII. THE SKELETON 



General Structure and Uses of the Skeleton. — First, bones form 

 a framework to which muscles are attached; thus they are used 

 as levers for purposes of movement. Second, they give protection 

 to delicate organs ; 

 they form a case 

 around the brain, and 

 spinal cord; as ribs 

 they protect the or- 

 gans in the body cav- 

 ity. Third, they give 

 rigidity and form to 

 the body. 



Laboratory Work on 

 the Skeleton of a Frog; 

 Comparison with the Skel- 

 eton of Man. — For this 

 purpose, clean skeletons 

 of the frog (these may 

 be prepared by careful 

 students) and a prepared 

 skeleton of man may be 

 used. This exercise may 

 be made of increased 

 value by using skeletons 

 of several different ver- 

 tebrates, for example, a 

 bony fish, frog, snake, 

 bird, dog or cat, and 

 rnan. The different re- 

 gions may be identified and homologies and analogies drawn between dif- 

 ferent bones and organs in the various skeletons. 



The skeleton of vertebrate animals consists of two distinct regions : a 

 vertebral column or backbone which, with the skull, forms the axial skeleton; 

 and the parts attached to this main axis, the appendicular skeleton (the 

 appendages). All skeletons of vertebrates have the same general regions, 

 the size and shape of the bones in these regions differing somewhat in each 

 kind of animal. 



In the axial skeleton of the frog, as well as in man, the vertebral column 

 is made up of a number of bones of irregular shape, which fit more or less 

 closely into each other. These bones are called vertebrw. Notice that the 



371 



Skeleton of the frog; S., skull; SC, scapula; R.U., radio 

 ulna; H., humerus; Ph., phalanges; MC, metacarpals; 

 C, carpals; V., vertebral column; UR., urostyle; P.G., 

 pelvic girdle; F., femur; TF., tibia and fibula; TS., 

 tarsals; MT., metatarsals. 



