VERTEBRATA. 257 



flight possesses a median Keel, (carina^) to afford an 

 increase of space for attachment of the great pectoral 

 muscles. Hence these birds are called carinatce. The 

 skull articulates with the spine by a single condyle, and 

 with the lower jaw by the intervention of a separate 

 bone, as in Reptiles. 



The beak is the bird's principal organ of prehension, 

 and differs in shape according to habits and food. The 

 pharynx is simple. The oesophagus varies in different 

 orders. Except in some aquatic birds, the food is re- 

 ceived first into a temporary stomach, or crop, which is 

 largest in grain-feeders. From this the oesophagus leads 

 to the true digestive stomach, which secretes the gastric 

 juice, (proventricidusl) and leads to the muscular stom- 

 ach or gizzard, (yentriculus bulbosus.) 



In tlesh-feeders this is thin, but in grain-feeders it is a 

 powerful triturating organ. The small intestine is short 

 in carnivorous birds and long in others. The large in- 

 testine ends in a dilated sac, the cloaca, which also re- 

 ceives the terminations of the urinary and generative 

 organs. 



The trachea is furnished with two larynges ; one at 

 the upper part, as is usual in animals, and one called the 

 syrinx, which is the principal organ of voice, at the bi- 

 furcation of the trachea into the two bronchi. Every 

 means are employed to render the respiration rapid and 

 complete. The lungs are large and cellular, and the 

 bronchial tubes not only divide continuously in them, 

 but conduct air into the general cavity of the abdomen 

 and to the interior of many of the bones. 



The feathers of birds are cutaneous growths, each 



TEB 



'UHIVE? 



