72 



FIRST LESSONS IN ZOOLOGY 



such movements the toes rest on the sohd yround, the body 

 is hfted and thrown forward. There are a number of 

 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. 42 shows the large muscles of the fore leg of a 

 cat. Each consists of a large central mass f<jrmed of the 

 muscular or contractile substance proper bound up into a 

 compact bod}' b}' connective tissues, with strings or bands 

 of connective tissue at the ends fastening the muscular 

 mass to the bones. These fastenings 

 are tendons. When the muscular sub- 

 stance contracts it of course pulls on the 

 two tendonous 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, with its fulcrum at the 

 end of the femur. The tibia is brought 

 toward the femur and we say that the 

 limb is flexed. Another muscle in con- 

 tracting will act on the tibia as a lever 

 also, but it brings the tibia back again 

 -Muscles on into a Straight line with the femur. 

 r',1""'!»r P^'°^This motion is called extension. For 

 Jeii- each part of the limb from hip to toe are 

 groups of muscles which flex and e.xtend 

 that part, the bones being levers and fulcra and points of 

 attachment. Most of these levers are of the kind called in 

 mechanics levers of the third class. ]\y them quickness of 

 motion is magnified. Thus by noting first what motions 

 an animal makes, and then, by dissection, examining the 

 muscles, the bones, antl their points and means of attach- 

 ment, we may come to unilerstand clearly the uses of 

 the muscles and skeletcni in any animal. 



Fig. 42. 



Hani aiiil 

 nings.) 



