YOUNG BIRDS AND RECORDS OF THE PAST 133 



Let us imagine the experiment made. We should find, 

 then, a curious somewhat mallet-shaped bone, the handle 

 being short and triangular. If we similarly treated the 

 upper end of the foot-bone we should find what is necessary 

 to complete the story — a flattened, oval plate of bone, of 

 which more presently. 



To find their like in the animal kingdom, we should have 

 to go to the nearest museum possessing the skeleton of one 

 of those monsters known as a Dinosaur, a giant reptile 

 happily for our peace of mind extinct ages ago. For 

 choice, we should seek out an iguanodon. Herein we 

 should find the same mallet-shaped bone at the end of the 

 shank, and the same oval plate capping the foot-bones, 

 answering to the sole-bones, " metatarsals." But while 

 in the bird these elements remain distinct only for a few 

 weeks, in the fossil, it is plain, they retained their identity 

 throughout life. 



Between the bird and the fossil, however, we should find 

 in this matter of the foot one striking difference. In the 

 reptile this oval plate forms a cap to three separate meta- 

 tarsal bones, or sole-bones as they are called in common 

 speech ; while in the bird there is but one. This difference, 

 however, is more apparent than real, for if this single shaft 

 be carefully examined, there will be found running down 

 its whole length two fine lines, one on either side of the 

 middle of the shaft. They are the lines of contact between 

 these separate shafts of bone, which have become blended 

 together, leaving but a faint trace of their earlier distinct- 

 ness, a trace which vanishes completely in the adult. 



That this is so we shall see at once if we go to the trouble 

 of examining the foot of an embryo, for here we shall find 

 these three bones as distinct as in the fossil reptile, as will 

 be seen by a comparison of our illustrations. Herein, 



