112 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Viewed from in front the superior border internal to the ascending process 

 extends downward the ventral until it reaches the inner margin, whereas in Antro- 

 demus this border extends inward about parallel with the ventral border. Were 

 the astragalus of Oeratosaurus detached, other differences might be observed. 



The calcaneum is so completely fused with the astragalus that the line of union 

 is quite obliterated. This bone appears to be wider than high, with a concave 

 proximal surface for articulation with the fibula, with which it is also closely ar- 

 ticulated. The outer surface is deeply concave. 



Measurements of the combined astragalus and calcaneum. Ceratosaurus nasicornis Marsh. No. 4735, 



U.S.N.M. 



mm. 



Greatest transverse diameter 130 



Greatest antero-posterior diameter of inner end 65 



Greatest antero-posterior diameter of outer end ' 53 



Greatest height of astragalus about ., 82 



Greatest height of calcaneum 37 



Metatarsals. — The metatarsals of Ceratosaurus nasicornis are described 1 by 

 Marsh as follows : 



The most interesting feature in the extremities of this dinosaur is seen in the metatarsal bones, 

 which are completely ankylosed, as were the bones of the pelvis. There are only three metatarsal ele- 

 ments in each foot, the first and fifth having apparently disappeared entirely. The three metatarsals 

 remaining, which are the second, third and fourth, are proportionally 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. 



In figure [1, pi. 24], these coossified metatarsals of Ceratosaurus are represented, and for comparison 

 the corresponding bone of a penguin is given in figure 0. In comparing these two figures it will be seen 

 that the three metatarsal elements of the dinosaur are quite as closely united as those of the bird. To 

 the anatomist familiar with the tarso-metatarsal bones of existing birds, the specimen represented in 

 figure 1 [pi. 24] will appear even more like this part in the typical birds than the one shown in figure 2. 



The position of the foramen, as seen in figure 1 [pi. 24], is especially characteristic 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 birds, living and extinct, with possibly the single exception of Archaeopteryx have the 

 tarsal bones firmly united, while all the Dinosauria, except Ceratosaurus, have these bones separate. 

 The exception in each case brings the two classes near together at this point, and their close affinity has 

 now been clearly demonstrated. 



It has been suggested 2 that the uniting of the metatarsals in Ceratosaurus was 

 due to a pathologic condition, but since there appears to be but little evidence of 

 exostosial growth on the bones I am inclined to believe it to be a normal but rather 

 unusual condition. That there is a tendency toward the fusion of the metatarsal 

 bones in some of the carnivorous dinosaurs is shown in several known specimens, 

 especially those of Tyrannosaurus, as pointed out by Osborn. 2 " He says they 

 exhibited a "less mobile arrangement of the metatarsals, because they show sutural 

 attachments but not actual coalescence in the middle portion of the shaft." 



An exceedingly aged individual would probably show coalescence, as they do 

 in Ceratosaurus. Marsh considered the first digit as having entirely disappeared, 

 but a roughened area on the posterior side of the shaft of metatarsal II (I, fig. 1, pi. 25) 

 apparently indicates the point of attachment of the retroverted digit as has been 



i- Amer. Jourp. Sci., vol. 28, 1884, pp. 161-162, figs. 1, 2. » Bull. Amer. Mus. Nat. His;., vol. 22, 1906, p. 294. 



2 Bauer, G., Amer. Naturalist, vol. 24, 1890, p. 301. 



