162 



DINOSAURS OF NORTH AMERICA. 



end fitting into the calcaueum. The tarsals of the second row are very 

 thin, and united to the metatarsals below them. 



THE METATAKSALS. 



One of the most interesting features in the extremities of Ceratosau- 

 rus is seen in the metatarsal bones, which are completely anchylosed, 

 as were the bones of the pelvis. There are only three metatarsal 

 elements in the foot, the first and fifth having apparently disappeared 

 entirely. The three metatarsals remaining, which are the second, third, 

 and fourth, are proportionately shorter and more robust than in the 

 other known members of the order Theropoda, and, being firmly united 

 to each other, they furnish the basis for a very strong hind foot. 



Flo. 4.— United metatarsal bones of Ceratomurue nasioornU Marsh; left foot ; front view. One- 

 fourth natural size. 



Fie. 5. — United metatarsal bones of great Penguin { Aptenodytes Pennantii G. R. Gr.) ; left foot; 

 front view. Natural size. 



/. foramen; //. Ill IT, second, third, and fourth metatarsals. 



In fig. 4, above, these coositied metatarsals of Ceratosaurus are repre- 

 sented, and in fig. 5 the corresponding bone of a penguin is given for 

 comparison. 



In comparing these two figures, it will be seen that the three meta- 

 tarsal elements of the dinosaur are quite as closely united as those of 

 the bird. To the anatomist familiar with the tarsometatarsal bones of 

 existing birds the specimen represented in fig. 4 will appear even more 

 like this part in the typical birds than the one shown m fig. 5. 



The position of the foramen, as seen in fig. 4,/, is especially charac- 

 teristic of recent birds, and, as a whole, the hind foot of this Jurassic 

 dinosaur was evidently similar to that of a typical bird. 



All known adult birds, living and extinct, with possibly the single 

 exception of Arcbaeopteryx, have the metatarsal bones firmly united, 



