the Skeleton of Diplodocus Garnegiei. 



369 



shows how on the reptilian plan the movements of humerus ■would 

 follow the arc ABC, and in this way the great breadth of this bone 

 would make it thick, or deep, just in the direction where strength is 

 required. Again, that broad spatulate end shown in Fig. 21 is really 

 another argument in the same direction. Looked at from a mechanical 

 point of view, it speaks volumes. Why should it have that large 

 rounded end unless its surface moved more or less in an arc and 

 attached rather loosely to this concavity ? Moreover, the glenoid 

 cavity, although not very well preserved, seems to exhibit a shape 

 more or less corresponding with such an outline (Figs. 20-3). The 

 crocodile's humerus is useful for comparison. 



Tail 



Body 



Neck 



Ft 



3?- 



Fig. 8. — Diagram to illustrate wrong articulation of the limb-bones of the 

 Diplodocus skeleton. The body, neck, and tail are shortened for con- 

 venience. 



Fig. 9. — Diagram showing working of humerus of Diplodocus (ground-plan). 



As mounted, this broad, spoon-shaped blade (see Fig. 6) is placed 

 directly at right angles to the scapula and general direction of the 

 glenoid cavity. Is it likely the big muscles attached to this broad scapula 

 could suddenly change their direction, and somehow twist themselves 

 on to the humerus? They would have to pass over a long and rather 

 sharp ridge. And, moreover, the surface of contact is so small as to 

 suggest a mere point of contact and not a proper broad surface. Such 

 a condition is absurd and unthinkable. Bear in mind that owing to 

 the great weight of Diplodocus the pressure on this ridge would be 

 tremendous. The muscles would be lacerated and after a time 

 actually severed. But on the other hand, by turning humerus round 

 90 degrees we get a suitable broad surface to which the muscles can 

 be attached without violently changing their direction. 



DECADE VI. — VOL. IV. — NO. VIII. 24 



