30 THE STORY OF THE BIRDS 



vertebrae, and nearly always with the terminal 

 portion of the caudal vertebrae which, fused to- 

 gether, form the Pygostyle or terminal triangular 

 plate in which the rectrices or tail-feathers are 

 carried. A typical avine vertebra consists of the 

 centrum, an arch, and two ribs. The arch as 

 already stated encloses and protects the spinal 

 cord. This type of vertebrae, with the facets or 

 articular surfaces saddle-shaped, is termed hetero- 

 ccelous, and is restricted to Birds. The ribs of 

 a bird are attached to the vertebrae firstly by a 

 capitulum or head, and secondly by a knob or 

 tuberculum. That portion next to the head 

 is termed the neck, and this is succeeded by 

 the shaft, composed of two pieces, the dorsal 

 and the ventral. To the posterior margin of the 

 dorsal section is generally attached a thin bony 

 blade termed the uncinate process. This pro- 

 cess is attached to the ribs (with the exception 

 of the last) of all birds (save the Screamer), and 

 is also present in some reptiles. When the 

 ventral section reaches and articulates with the 

 sternum, the rib is a " true " one ; but if the 

 sternum is not reached it becomes a "false" 

 rib. Ribs according to their position are 

 classified as follows : cervical, cervico-dorsal, 

 thoracic, and lumbar. The number in these 



