64 A FIELD GUIDE IN NATURE-STUDY 



The hind leg. Notice the cat's hind leg. How many joints does it 

 have ? Feel it carefully and see. How do these joints compare in number 

 and position with those of the foreleg? Study the hind leg of the dog, 

 squirrel, and rabbit. Compare with that of the cat. Sketch the hind leg 

 and reduce to diagrams in the same way as already described for the foreleg. 

 Write a description of what you have observed regarding the structure of 

 the fore and hind legs of these animals. To hold one set of facts in mind 

 and compare it with another and still another and finally with a whole 

 series to see a fundamental unity underlying superficial differences is to 

 take a step in advance of mere observation. 



Vertebrates. Feel of the cat and dog to gain an idea of the skeleton. 

 Feel the vertebral column, extending from head to tip of tail. Do horses 

 and cows have a backbone ? Do we ? What other animals that you 

 know have a backbone ? Feel the ribs and breastbone; then note that the 

 head is a bony mass. Feel the shoulder blade that fastens the foreleg to 



FIG. 5. Diagram of forearm 



the body. When the cat is not standing on her feet this bone, to which 

 the foreleg is attached, may be easily moved about, as it is simply imbedded 

 in the muscle, not fastened to the other bones. Demonstrate this to your 

 own satisfaction. Feel the hip bone, to which the hind legs attach and 

 which fastens, in turn, to the vertebral column. Are there bones in the 

 legs? What is their relation to the joints that we have noted and dia- 

 grammed ? Why does a cat have bones ? Does an oyster have bones ? 



Is a cat's hind leg straight, like yours? How is the leg bent in the 

 process of jumping ? Try a jump and notice your movements. Now can 

 you tell why the cat's hind leg is always bent ? Watch the cat jump down 

 from a table. How does she use the hind legs ? On which legs does she 

 alight? How does the way in which the foreleg is attached to the body 

 make it easy for her to alight ? How could the structure of the legs help 

 the cat in hunting ? Which has the straighter legs, a dog or a cat ? Which 

 can run faster? Think of other animals that can run fast and far. Do 

 they have straight legs or legs bent like a cat's hind leg ? Make a list of the 

 very speedy animals and those vertebrates that do not run well. Note the 

 length of the leg and the straightness of the leg. 



Structure and use. How many toes has the cat ? dog ? rabbit ? pig ? 

 cow ? horse ? Why can puss walk so quietly ? Feel the underside of her 



