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TEXTBOOK OF ZOOLOGY 



protection and temperature regulation in most of the groups of ver- 

 tebrates. Such structures as scales, shells, feathers, hair, nails, horns, 

 and even enamel of teeth are of this type. 



Primitively the notocJiord is the original endoskeletal structure of 

 the chordate group. Around it are developed the basic structures of 



Ska// 



Ceri//ca/ 

 vertebrcxe 



Scapu/a 



Sternum 



Thoracic 

 vertebrae 



Lumbctr 

 vertebrae 



Sccrum 



Mefacarpa/s 



Cranium 

 Orbit 



Mandib/e 



C/av/c/e 



■Humerus 

 Rib 



Pe/vis 



Radius 

 Utna 

 ^Carpa/s 



Hc^nd 



Fig. 218.- 



Tibia 



Metatarsals 



-Human skeleton. (From Wolcott, Animal Biology, published by the 

 McGraw-Hill Book Company.) 



the vertebral column which functions as the principal axial support 

 of all vertebrates. The sternum, girdles, and paired limbs have 

 developed with the terrestrial life of vertebrates and the necessity 

 for locomotion on land. 



