14 OLIVER P. HAY 



relatively short femora diverge downward so that the knees are 

 almost always farther apart than are the great trochanters, some- 

 times much farther. Nevertheless the feet in walking are generally 

 placed on the line of direction, a result brought about through the con- 

 vergence of the elongated middle and lower segments of the two legs. 

 If they are not brought close to this line, as in the short-legged ducks 

 and geese, the walk becomes a waddle. 



The femur of Allosaurus, of the Upper Jurassic, possesses a head 

 that projects strongly inward; and this was provided with a well- 

 defined smooth articular surface, which is elongated transversely to 

 the animal and convex from front backward. The surface of the 

 ilium against which this head fitted is also smooth. Now the confor- 

 mation of the head of the femur and the ilium is such that the femur 

 must have diverged considerably from its fellow, thus widely separat- 

 ing the knees. The tibia is shorter than the femur, and the inner 

 condyle appears to stand lower than the outer. The metatarsus is 

 relatively short. I see no way, therefore, for the feet to be brought, 

 except with unusual effort, near the line of direction in walking or 

 near each other in standing. The limbs of Allosaurus may be com- 

 pared to those of the penguins, although in Allosaurus the femora 

 may not have been directed so strongly forward and the feet may have 

 been more digitigrade. It would probably be very difficult for the 

 penguin to plant its feet one in front of the other in walking. I believe 

 therefore that Allosaurus had a wide trackway and that when it walked 

 and ran it preserved its equilibrium by whisking its tail from side to 

 side. 



Examination of a femur, accompanied by the tibia and the fibula, 

 in the U. S. National Museum, apparently that of Tyrannosaurus, 

 shows the same form of the head of the femur that is found in Allo- 

 saurus, thus making it probable that this dinosaur also had a straddling 

 gait. Professor Osborn (Bull. Amer. Mus. Nat. Hist., xxii, p. 293) 

 presents a figure of the femur of Tyrannosaurus. He says that the 

 plane of the head makes an angle of 45° with the axis of the vertebral 

 column, and that therefore the distal ends of the femora are approxi- 

 mated. Whether the angle is in front of or behind the head of the 

 femur is not stated. In Allosaurus the head is directed inward and 

 forward. The effect of this would certainly be to throw the knees 

 outward and to plant the foot farther away from the line of direction. 



