4io 



ZOOLOGY 



pletely surrounded by protective membranes. The cavity 

 between the true amnion and the body wall (Fig. 208, am. c.) 

 is the amniotic cavity and may be filled with a fluid. 



441. Classification of Aves. 



Subclass I. SaururcB (reptile-tailed). These are extinct birds 

 related to the extinct reptiles the dinosaurs in having a 

 vertebrated tail, and jaws bearing teeth. Each vertebra of 



FIG. 210. 



FIG. 210. Apteryx australis. From Romanes. 



Questions on the figure. What peculiarities does this bird present? What 

 does Apteryx mean? What is the distribution of this species? What are its 

 nearest relatives among the birds? 



the tail possessed a pair of feathers, the tail thus having a row 

 of rectrices on either side. 



Archaeopteryx, of which two specimens have been found in 

 the lithographic quarries of Bavaria, represents the group and 

 was about the size of a crow (Pig. 209). 



Subclass II. Neornitkes (modern birds). This group is 

 characterized by the reduction and fusion of the tail vertebrae 

 in such a way that the tail feathers (rectrices) are arranged 

 in a semicircle (or sometimes wanting). Teeth are wanting 

 except in some extinct forms, which stand intermediate between 

 the Saururae and the recent birds. 



Division I. Ratitcs (flat). These are running birds with a 



