8 OLIVER P. HAY 



Memoirs, plate IV, fig. 2. The so-called head of the femur is toward 

 the left, against the pubic process. According to this figure, there 

 was room in the acetabulum for the femur, standing at right angles 

 with the pelvis, so that it could rotate on its longer axis and could 

 swing backward and forward. Such movements would be required 

 in case the reptile walked as does the crocodile. In the execution of 

 these movements it would probably happen, as it does in the lizards, 

 that some part of the head would at times be outside of the acetabulum. 

 in order to show the resemblance of this joint in the lizards to the one 



FIG. 2 LEFT ACETABULUM, CONTAINING SECTION OF PROXIMAL END OF 



FEMUR; THIS SECTION SHOWN BY HEAVY LINE. X T \r5 *"&* ILIUM; isch., 

 ISCHIUM; pub., PUBIS. 



depicted, a drawing (Fig. 3) is shown of the acetabulum and head of 

 the femur of Metapoceros. 



However, the articulation at the hip was probably not effected in 

 just this way. It appears that in some cases the proximal end of the 

 femur is wider than the acetabulum. Dr. E. S. Riggs informs me 

 that in Apatosaurus (Brontosaurus) and Brachiosaurus the upper end 

 of the femur is about 23 inches wide, exceeding the fore-and-aft 

 diameter of the acetabulum by 3 or 4 inches. I do not regard this 

 fact as wholly irreconcilable with the view illustrated by figure 2, the 

 head of the femur having sometimes a greater diameter than the 

 acetabulum, as in the land tortoises. Nevertheless, I will not argue 

 the matter. A somewhat different arrangement at the articulation is 

 more probable. 



