THE EXTINCT DINOSAURS 



2393 



and the United States, in which the whole backbone was so permeated by air cavi' 

 ties as to be little more than a mere shell of bone. 



The whole of the dinosaurs mentioned above agree with one another 

 l-Like - n p OSSess j ng a pelvis approximating to the crocodilian type; that is to 

 say, the pubis or anterior lower bone of this part of the skeleton is in- 

 clined downward and forward, and thus diverges in the form of an inverted Ffrom 

 the backwardly and downwardly directed ischium, or posterior lower bone, as shown 



SKELETON OF THE CI.AOSAUR, ONE OF THE BIRD-LIKE DINOSAURS. 



(One-fortieth natural size.) 

 (After Marsh.) 



in the figure on p. 2359. On the other hand, in the bird-like dinosaurs the main 

 bar of the pubis is inclined backward, parallel to the ischium, while it has 

 a secondary plate projecting forward. In this parallelism of the pubis and 

 ischium these dinosaurs resemble birds (see the figure in Vol. III., p. 1462), and 

 birds alone; and from this and other features it is pretty certain that the latter are 

 derived from reptiles more or less closely-allied to this or the preceding group of 

 dinosaurs; the resemblance in the one case being closest in the structure of the 

 pelvis, and in the other of the hind-limb. All the bird-like dinosaurs are further 



