298 THE VERTEBRATE SKELETON. 



a claw. The second digit is considerably the longest, while 

 the third includes four phalanges. The three bones of the 

 pelvis probably remained distinct throughout life. The tarsals 

 are ankylosed respectively to the tibia and metatarsals as in 

 other birds. The metatarsals are ankylosed together, and the 

 pes has four digits. 



Subclass II. NEORNITHES. 



To this subclass may be referred all known birds except 

 Archaeopteryx. They all agree in having a short tail whose 

 component vertebrae are commonly ankylosed together form- 

 ing a pygostyle. The three metacarpals do not all remain 

 distinct. The bones of the pelvis are ankylosed together, 

 and to a large though variable number of vertebrae. There 

 are three orders, the Ratitae, Odontolcae, and Carinatae. 



Order 1. RATITAE. 



The Ratitae differ from Archaeopteryx and the great 

 majority of Carinatae in being flightless. The bones are 

 generally not pneumatic, containing marrow instead of air, 

 in the Ostrich however they are very pneumatic. The tail 

 is short and the posterior caudal vertebrae are generally 

 ankylosed together forming a pygostyle. The pectoral girdle 

 has comparatively a much smaller size than in Carinatae, 

 clavicles are small or absent, and the scapula and coracoid 

 lie nearly in the same straight line. The ilium and ischium 

 do not as in Carinatae unite posteriorly, and enclose a 

 foramen except in very old Rheas and Emeus. The quadrate 

 articulates with the cranium by a single head. The vomers 

 unite and form a broad plate, separating the palatines, ptery- 

 goids and basisphenoidal rostrum. 



The anterior limbs are greatly reduced in size or even 

 absent, while the posterior limbs are greatly developed and 

 adapted for running. The tibia and fibula are quite distinct. 



