170 



STRUCTURE OF THE VERTEBRATES 



are of an entirely different nature. The digits sliow a great de- 

 generation, with a fusion of the carpals. AVing expanse is gained 

 with the feathers. 



There are other distinct modifications, for example digging or 

 burrowing, and there are variations of the above. Specializations 

 of the appendages are more frequent and more easily observed 

 than in any other part of the body. Environment places a high 



Fig. D Bat 



Fig. 101. Flying Adaptations. Flying Reptiles and Mammals (A and D) 



have elongated digits with membranous flaps stretched between them to 



give surface resistance. Increased area is given birds by the feathers. 



