"22 THE STORY OF REPTILE LIFE. 



the skin, and the next the thick layer of muscles 

 underlying this. Both are wanting in the trunk 

 of the Tortoises ! When we come to look deeper 

 into this anomalous state of things we find that 

 the bands of bone which we have just described 

 as running at right angles to the long axis of the 

 skeleton, that is to say the bands of bone running 

 from side to side, have a strangely complex 

 history. Originally, as we have said, nodules of 

 bone embedded in skin, they have, with the 

 wasting of the underlying muscles, come to lie 

 at first directly upon the ribs, and later, fusing 

 therewith, have ultimately replaced even these 

 almost completely. So much so, that all that re- 

 mains to-day, of what appear to be complete ribs, 

 is the head thereof, or the portion which joins 

 the backbone and the tip, or that portion which 

 supports the little bones which form the margin 

 of the shell. This we know, because in the very 

 young tortoise comp]ete ribs are present, but as 

 development proceeds, all save the two ends 

 become absorbed and replaced by the bones, origin- 

 ally, as we have said, belonging to the skin. 

 Exactly how this is done requires an intimate 

 knowledge of the changes which may take place 

 in the tissues of animals, and these we cannot 

 attempt to deal with here. Those who would 

 verify these statements must consult more 

 technical works than this little book, and 

 bring with them at the same time the results 

 of a scientific training. 



The history of the breastplate of the tortoise 

 is no less strange. Like the shell this is made 

 up, externally, of symmetrically arranged plates 



