232 



BARON NOPCSA ON THE 



[Feb. 19, 



many cursorial Mammals, were not only set the problem of 

 developing a flexible doi'sal vertebral column, which was attained 

 by development of convexo-concave intervei'tebral ai-ticulation, 

 but that to this, in consequence of the position of their head, they 

 had to add strength in the vertical direction, which could only be 

 attained by developing the attachment surfaces for the musculus 

 longissimus dorsi on the neiu^al spines and the producing of 

 hypapophysis-like knobs on the cervicals. This, moreover, is the 

 first consideration adduced since 1887 that shows us that the 

 vertebi'al column of Iguanodon, though provided with ossified 

 tendons, cannot have been altogether rigid. Text-fig. 79 is in- 

 tended to show the highly modified foot of the Cretaceous Dinosaur 

 Ornithomimiis, and can be compared with the feet of Dipits and 

 Alactaga (text-fig. 80). 



Text-fig. 79. 



Text-fi" 



Text-fig. 79. — Hind limb of Ornithomimus. 



80. — Hind limbs of Diptts (left) and Alactaga (right 



Birds. 



Leaving Dinosaurs and turning to Birds, we observe the follow- 

 ing salient points : — 



The first and most primitive Bird we know, Archceopteryar 

 (text-fig. 81), shows not only a perfectly bird-like femur and tibia, 

 bvit also tridactylism, and this is, as demonsti-ated by Dinosaurs 

 and the Dipus-\ike rodents, a prominent feature of bipedal 

 cursorial or saltatorial specialisation, Avhile it never occurs among 

 arboreal forms. 



The pelvis of A 7-chceopteryx, moreover, is essentially that of a Bird , 



