BETWEEN TYPICAL EEPTILES AND OTHEE ANIMALS. 189 



cesses to articulate with the pterygoid ; and the presphenoid is 

 similax'ly prolonged forward between the pterygoids. These 

 bones, though smaller in the bird and of different form, similarly 

 diverge behind, and unite with the inner sides of the quadrate 

 bones, lapping behind the process which the quadrate of the bird, 

 iu common with that of the Ehynchocephalian, sends forward and 

 inward. 



There is a general resemblance between the form of the dorsal 

 vertebrae in Monitor and in birds, so far as concerns the shape of 

 the neural spine, the length of the centrum, and the concave side- 

 to-side outline of the articulation seen on the under surface ; but 

 Lizards, unlike birds, Crocodiles, and Salamanders, have no trans- 

 verse process, which in the neural arch of birds forms a platform 

 down the back, to which the second head of the rib articulates. 

 The elongation of the neck, the shortness of the tail, and the 

 anchylosis of the sacral vertebrae in birds are unlizardlike. 



The pectoral arch of Struthious birds may be compared to 

 that of Chamcdleon. The sternum is similar, and gives attach- 

 ment to short broad coracoids, which make the acetabulum for 

 the humerus, with an elongated unexpanded scapula. 



Carinate birds have the clavicles as well developed as in ordi- 

 nary Lizards ; and then, as in Monotremes, they similarly arti- 

 culate with the small acromial process of the scapula, but do not 

 reach beyond it as in Lizards. In the Penguin the scapula is 

 almost as much expanded as in Lizards ; but the acromion is 

 short and not given off from the middle of the front margin, but 

 from near the union of the bone with the coracoid. If the keel of 

 the bird's sternum represents the interclavicle of Lizards, it is not 

 often that it preserves, as it does in the Shrike, the transverse bar 

 of the T- shape ; the interclavicle of Iguana has an incipient keel ; 

 and, in general, the interclavicle of the bird may be supposed to 

 be formed, like that of the Skink, in a +, if it exists at all. 



The ribs of true Lizards never show the epipleura characteris- 

 tic of birds, which are well developed in Hatteria ; nor do the ribs 

 usually consist of so few as two elements, though often as many 

 sternal ribs articulate with the sternum in Lizards as in birds. 



The humerus corresponds closely with that of carinate birds, 

 and from the Parrot differs chiefly in not having the radial crest 

 so much compressed, in not having the ulnar process excavated 

 for a pneumatic foramen, and in having the distal end more ex- 

 panded from side to side. 



