ANIMAL PHYSIOLOGY 



S3 



slender bone in the body of the foot. These are the 

 metatarsals. At the end of each metatarsal is a series 

 of three bones which forms the skeleton of each toe. 

 All of these bones together constitute a system of levers 

 which the muscles of the leg can draw up in a some- 

 what folded position, and then straighten out with quick- 

 ness and force. Since during such movements the toes 

 rest on the solid ground, the body is lifted and thrown for- 

 ward. There are several strong muscles which make the 

 pulls for these motions, but a single pair may be studied as 

 an example of the method of attachment and action of all. 



Fig. 19 shows the large muscles of the 

 fore leg of a cat. Each consists of a large 

 central mass formed of the muscular or 

 contractile substance proper bound up 

 into a compact body by connective tis- 

 sues, with strings or bands of connective 

 tissue at the ends fastening the muscular 

 mass to the bones. These fastenings are 

 tendons. When the muscular substance 

 contracts it of course pulls on the two ten- 

 donous ends. If one end of a muscle 

 in the hind leg is attached to the hip- 

 bone it cannot move, but the one fastened 

 to the tibia moves this bone as a lever, 

 fulcrum at the end of the fe- 



FIG. 19. Muscles on 

 side of fore leg of mur. The tibia is brought toward the 

 cat (After Reigh- f emur ^ anc i we say t h at the limb is flexed. 



ard and Jennings.) . . 



Another muscle in contracting will act on 

 the tibia as a lever also, but it brings the tibia back again 

 into a straight line with the femur. This motion is called 

 extension. For each part of the limb from hip to toe are 

 groups of muscles which flex and extend that part, the 

 bones being levers and fulcra and points of attachment. 

 Most of these levers are of the kind called in mechanics 



