90 



The Bird 



Fig. 63— Pelvic arch of a Dinosaur 



bone extending backward from the thigh-socket, sepa- 

 rated from the ischium 

 (except at the extreme 

 end) by a long open sHt. 

 In other animals these 

 bones are as different in 

 shape as can be imagined, 

 but, almost without excep- 

 tion, the position of each 

 is relatively the same. The 

 extreme extension, forward 

 and back, of the ilium 

 above the back-bone, thus 

 joining with more vertebrae, 

 is directly connected with 

 two-legged erect locomo- 

 tion. A parallel condition 

 is found in some Dinosaurs 

 — those extinct giant rep- 

 tiles — certain of which 

 walked more or less on 

 their hind legs. 



Another fundamental 

 resemblance is found be- 

 tween the thigh -girdles of 

 Dinosaurs and other rep- 

 tiles and that of a bird in 

 the egg. As is shown in 

 Figs. 63-65, the pubis slants 



slightly forward in both reptile and embryo bird; but in 



Fig. 64. — Pelvic arch of an embryo bird, 

 to show similarity ot the two as 

 contrasted with Fig. (5. 



Fig. 65. — Pelvic arch of an adult bird. 

 (The three figures by courtesy of 

 Prof. H. F. Osborn.) 



