28o 



BIOLOGY AND HUMAN LIFE 



a 



Fig. 132. Some curious but useless relics 



In the glass snake, a kind of lizard (Anguis jragilis), the buds of the front legs are 

 present during an early stage of development, a, but the fully formed animal is foot- 

 less. In the porpoise {Phocaeua communis) the buds of the hind legs (or flippers) 

 are present during an early stage of development, b, but the fully developed animal 



has only front flippers 



Fig. 



1-^ -^ 

 00- 



Human vertebrae 



Each of the units of the spinal column consists of a main body (with an arch on the 

 dorsal side) and various projections. The openings in the arches make up a tube, 



or canal, in which the spinal cord lies 



from the floor of the mouth, and acquires a great variety of 

 forms and functions in different species of backboned ani- 

 mals : in most cases it is either a food-getting organ or one 

 that moves food around during the process of chewing. 



