THE POSE AND LOCOMOTION OF DIPLODOCUS 



II 



the greater part did so enter. Doubtless, when the leg was extended 

 forward, a considerable part of the cartilage covered surface on the 

 fibular border was out of the cup, and when the leg was directed back- 

 ward the rounded anterior part of the head was out. This is exactly 

 what happens in the lizard and, for that matter, in most animals. 

 The head of the femur of Diplodocus, compared with that of the 

 crocodile, differed in having its long axis coincident with the plane 

 through both condyles; while in the crocodile the head is twisted 

 from the plane mentioned about 75°. Figure 7 represents the same 

 humerus as figure 6, but lines are drawn across the head to show the 

 varying relations of the bone to the acetabulum. The line aa may 



FIG. 6 PROXIMAL END OF FEMUR OF DIPLODOCUS. X A- THE DOTTED LINE 

 SHOW THE LIMITS OF THE CARTILAGE. 



be regarded as a section through the acetabulum when the leg is 

 thrown far forward; bb, when the leg is at right angles with the body; 

 cc, when the leg is thrown well backward. Of course, as the leg is 

 swung from front to rear, the femur will turn also on its long axis. 

 As is well known, the acetabulum of the Sauropoda is widely open 

 in the skeleton. I am not aware that any one has discussed the way 

 in which in life this opening was filled. It seems improbable that it 

 was shut simply by membrane, for this would have been too yielding 

 to the pressure of the head of the femur, if inserted as generally sup- 

 posed. It seems most probable that the opening was occupied by 

 a mass of cartilage, an imossified portion of that common cartilage 

 from which were developed the ilium, the pubis, and the ischium. 

 This would have formed a firm concave bed on which the convex head 



