SAUKOPSIDA. 



Although we naturally associate the birds with the warm- 

 blooded, hair-bearing animals (Mammals), yet structurally 

 they are more allied to the reptiles; a fact indicated by our 

 heading, which means lizard-like. Some of these common 

 features are a body-covering of scales or feathers derived 

 from the epidermis; the articulation of the skull with the 

 neck by a single condyle ; the existence of the quadrate as a 

 suspensor (p. 37) of the lower jaw, the presence of true 

 ribs, a three- or four-chambered heart, no functional gills, 

 large eggs with an abundance of yolk, and the existence of 

 a cloaca into which digestive, reproductive and excretory 

 organs empty. There are two classes of Sauropsida. 



CLASS I. REPTILIA (p. 64). 



CLASS II. AVES (p. 71). 



85, 



