THE POSE AND LOCOMOTION OF DIPLODOCUS 9 



Certain principles must be regarded as indisputable. One of these 

 is that primitively, in the common ancestor of the dinosaurs, the 

 crocodiles, and the lizards, probably in the early dinosaurs themselves, 

 the whole proximal end of the femur constituted the anatomical head. 

 Another is that before there could be any such structures and confor- 

 mations of these as w^e find at the hip joint of Allosaurus, for instance, 

 or of Trachodon, every possible stage from the one just described must 

 have been passed through. Through countless generations the thigh 

 must gradually have assumed a more and more forward position in 

 habitual locomotion. While muscles and nerves were being trained 



FIG. 3 ACETABULUM OF LIZARD METAPOCEROS, CONTAINING SECTION OF 

 HEAD OF FEMUR. X 2. SECTION OF FEMUR SHOWN BY HEAVY LINE. ALSO 



SIDE VIEW OF FEMUR X 2. Fcm., FEMUR; U., ILIUM; isch., ischium; ptib., 



PUBIS. 



to this end the femur must have been developing a projecting head, 

 that part of the proximal end on the fibular side was being excluded 

 from the acetabulum, and the rotation of the proximal end of the 

 femur around a perpendicular axis was being changed to rotation 

 around a horizontal axis, which in mammals would pass through both 

 femoral heads. Now, as regards the hinder leg and the hip joint, at 

 what stage in the long journey indicated above, do we find Diplodocus? 

 Obviously those who believe that this animal ought to be set up on its 

 legs in the way seen in drawings, plaster restorations, mounts of the 

 actual bones, and the plaster facsimiles of the skeleton that are being 

 distributed over the world, must hold that Diplodocus had reached 



