BONES OF THE LEG AND WING OF BIRDS. 179 



of an embryo bird greatly enlarged, showing the bones in 



place. 



At this early stage, not only the rnetatarsal bones are 



seen separate, but the bones of the tarsus, four in number, 

 are well marked and distinct. 1 



The many strange modifications in the shape and propor- 

 tions of the legs of vertebrate animals are accompanied by 

 similar changes in the arrangements, number, and proportion 

 of the bones of these parts. 



Thus, in the short leg of the salamander (see Fig. 152) 

 the bones of the tarsus occupy a space about as long as that 

 of the metatarsus. In birds, on the contrary, the tarsus is 

 very short, while the metatarsus is very long. 



159. If the pupils will observe the hind-leg of the toad 

 or frog, they will see that not only is it much longer than the 

 fore-leg, but that an extra joint seems to be added in the foot. 

 An examination of the bones shows that the first two tarsal 

 bones are very long, while the other tarsal bones are very 

 short ; so that in this case the tarsus combined is much longer 

 than the metatarsus. The following figure represents the 

 right hind-leg of a young toad while still in the tadpole 

 state, though the adult shows the same features. 



The above brief lessons on the vertebrates do not even 

 embrace an outline of the structure and habits of any of 

 the classes, and they are given only as suggestions toward a 

 method of study, and to point out the essential paths to fol- 



1 The author has seen the tarsal bone, marked e, in the heron, tern, and sea- 

 pigeon. 



