190 MB. H. Q. SEELET ON OSSEOUS BESEMBLANCES 



The ulna and radius rather resemble those of StrutLious than 

 carinate birds, since carinate birds have not the proximal end of 

 the ulna so large, or the whole bone so much compressed, and 

 they usually have the distal end impressed mesially so as to make 

 the articulation pulley-shaped. In Struthious birds, too, the 

 distal end of the bone is more expanded from side to side. The 

 radius corresponds with the Ostrich better in proportion than in 

 the form of the articular ends. 



The resemblances in the remainder of the skeleton are very 

 slight. Even the femur, though similar in proportion, differs in 

 wanting the external trochanter, and in having an internal tro- 

 chanter (which in birds is not developed), in having the proximal 

 articulation large and terminal instead of at right angles with 

 the shaft as in birds, and in having the condyles of the distal end 

 less divided in those few Lizards which, like the Monitor, show 

 indications of a dividing groove. 



The phalanges are often similar, and the claws are compressed 

 from side to side. 



§ 3. Tlie Crocodilian Characters of Lizards. 



JJromasUx and Iguana are Crocodilian in having the frontal and 

 parietal bones single and the nasals double. The frontal boiie 

 similarly divides the orbits. The downward direction of a process 

 of the pterygoid and of the transverse bone, so that they fall 

 within the lower jaw, is Crocodilian. 



Those Lizards (like the white Skink) which after the first two 

 vertebrae have cervical ribs, never have them of the j^-shape with 

 double heads which characterizes Crocodiles. 



Only in the earlier dorsal vertebrae of the Dragon are there 

 short transverse processes to the vertebrae ; but they are given off 

 from the centrum, and are never notched for ribs after the 

 manner of Crocodiles, but are single-headed and shorter and 

 stronger. In the tails of many Lizards, however, the transverse 

 processes are even more developed than in the Crocodile, especi- 

 ally in JJromasUx ; and in Lizards the vertebrae are more nume- 

 rous. They usually have the articulation of the centrum oblique, 

 while in Crocodiles it is vertical ; and in Crocodiles the centrum 

 is more compressed from side to side. In the young Crocodile 

 the articular fiices of the caudal centrum are flat or slightly 

 convex as in mammals, and so far unlike Lizards'. 



The pectoral arch of the Crocodile differs from that of true 



