4l6 THE PIGEON. PHYLUM CHORDATA 



foveae (p. 466). The visual acuity of the general surface of the 

 retina of most birds is probably as good as that of the fovea 

 of man. 



BIRDS AND REPTILES 



Warm-blooded though they are, birds are more akin to reptiles 

 than to mammals. This is expressed in many details of their 



Fig. 330. — Restoration of ArchcBOpteryx. — From Thomson, after Pycraft. 



The figure shows the teeth in the jaws, hints of the biserial tail feathers, and the three clawed digits on 

 the outstretched wings which are seen from the ventral aspect. 



anatomy — the structure and articulation of the lower jaw, 

 various other features of the skull, the ankle joint, the organs 

 of reproduction, the carriage of oxygenated blood by the right 

 systemic arch, the nucleated red blood corpuscles, the scaly legs, 

 etc. An interesting link between birds and reptiles is the extinct 

 ArchcBOpteryx (Fig. 330), of which there are two specimens 

 from the Upper Jurassic. These creatures were, as far as is known, 

 birds in all essential features, but had, like a reptile, teeth, free 

 fingers on the hand, and many vertebrae in the long, flexible tail. 



