OUR ANCIENT RELATIVES 



anatomists have long regarded as standing far 

 below the grade of the sharks in the scale of 

 vertebrate life. In some of these fossils the infil- 



FiG. 4. Some of Our Earliest Known Kinsfolk. 

 Upper Silurian and Devonian Ostracoderms. 



For details, see pp. xiii, xiv. 



trated mud has made a natural cast of even the 



principal nerves and blood vessels of the head, so 



that Stensio has been able to show that they com- 



11 



