THE MOTIONS OF ANIMALS 



71 



motions of the eyes, feelers, and respiratory organs are 



well performed. 



In the vertebrates the skeleton is mainly developed 



from tissues within the body and is called in consequence 



the endoskeleton. Even more than 



in the invertebrates it is a system 



(fig. 40) of levers, fulcra, and points 



of attachment for muscles to work 



with, and is as important a part of the 



organs of motion as is the muscular 



system itself. 



To illustrate the use of the skele- 

 Fic:. 40. — Biceps muscle . r , ^ , 



attached to radius, in ^on of a vertebrate we may e.xamme 

 arm of man; to show the bones of the hind legs of a cat 



how bones and muscle ^ _,, , ^ 



act as levers. (After ("g- 4i)- The upper bone, the femur, 

 Jenkms.) jg attached by a joint to the large 



irregularly shaped bone called the ilium, which is firmly 

 bound to the backbone. Below the femur are two 

 bones, the largest, called tibia, being bound by a joint 

 to the femur. Below the tibia are a group of bones, the 

 tarsal bones, pretty 

 firmly fastened to- 

 gether. The largest 

 makes a joint with 

 the tibia. Each of 

 the four tarsal bones 

 toward the toes make 



a joint with a slender Fig. 41. -Skeleton of cat. (After Reighard 

 bone in the body of and Jennings.) 



the foot. These are the metatarsals. At the end of 

 each metatarsal is a series of three bones which form the 

 skeleton of the toes. All of these bones together consti- 

 tute a system of levers which the muscles of the leg can 

 draw up in a somewhat folded position, and then 

 straighten out with quickness and force. Since during 



