OEETAGEOUS VERTEBRATE FOSSILS. 519 



was one of the most highly specialized of dinosaurs, and in the structure 

 of tin- feet the most bird-like of any yet discovered, as shown in figs. S3 to 

 86, "ii the opposite page. 



On the distal part of the tibia represented in fig. 83, the astragalus is 

 seen in place, with a very large ascending process, larger than in any 

 dinosaur hitherto known. The calcaneum is also shown in position, hut the 

 slender fibula is absent. This bone was complete, hut of little functional 

 value. The tibia and all the Larger limb hones were hollow, with thin walls, 

 as indicated in the section, fig. 83, c. The almost exact correspondence of 

 these different parts in some recent birds and the present reptile will he 

 manifesl to every anatomist. 



The most striking feature of the foot belonging with the reptilian tibia 

 is shown in the metatarsals represented in fig. 84, a. These are three 

 in number, and are in the same position as in life. They are the three 

 functional metatarsals of the typical Ornithopoda and <<( birds. The distal 

 ends of these bones correspond in size and relative position in the two 

 groups, hut here, in the present specimen, the reptilian features cease, and 

 those uf typical birds replace them. In all the reptiles known hitherto, 

 and especially in dinosaurs, the second, third, and fourth metatarsals are 

 prominent in front, at their proximal ends, and the third is usually the 

 largest and strongest. In birds, the place of the third is taken above by 

 the second and fourth, the third being crowded backward and verv much 

 diminished in size. 



This character is well shown in the second, third, and fourth metatarsals 

 of a youngturkey, with the tarsal bones absent. In the reptilian metatarsals 

 seen in fig. 84 the same arrangement is shown, with the tarsals in place. 

 The second and fourth metatarsals have increased much in size in the upper 

 portion, and meet each other in front. 



The third metatarsal, usually the largest and the most robust throughout, 

 here diminishes in size upward, and take- a subordinate, posterior position, 

 as in birds. The correspondence between the metatarsals of the bird ami 

 reptile are here as strongly marked as in the tibiae and their accompanying 

 elements, above described. 



In fig. 85 the three phalanges represented belong with the second 

 metatarsal, and were found together in place. 



