144 



CHARACTERS OF VERTEBRATE ANIMALS 



of the lower jaw is made up of several pieces instead of only 

 one as in a mammal. 



The backbone is very long and there are remarkable contrasts 

 between its several regions, for whereas the neck vertebrae are 

 united together by saddle-shaped surfaces so as to give extra- 

 ordinary flexibility, the vertebrae of the trunk are largely fused 



PARIETAL 



FRONTAL 



CARPO METACARPUS 



Fig. lOT. — Skeleton of Pigeon 

 A, Skull; B, vertebra and rib (front view); c, sternum and shoulder-girdles; D, wing; E, pelvis and tail; F, leg. 



together so as to confer great rigidity, an important matter in 

 connection with the requirements of flight. What is called the 

 " sacrum " in a pigeon is made up by the union of vertebrae 

 belonging to very different regions, including one thoracic, six 

 lumbar, two sacral proper, and five caudal. The remaining 

 vertebrae of the abbreviated tail are ten in number, and the last 

 four of them are fused into a laterally-flattened ploughshare bone^ 

 which supports the tail-quills. 



Since the walls of the thorax are fairly mobile in a bird, 

 and by their movement help in breathing, the breastbone and 

 ribs are hinged on to the backbone so as to permit of this. 



