A VES. 449 



One of the most interesting facts of bird-structure is the 

 existence of some birds which have lost their characteristic 

 power of flight. In Chap. VI I. we have already seen that 

 flightless birds and insects are a feature of oceanic islands, 

 but they are not confined to these regions. In certain 

 instances great increase in size and the acquirement of 

 strong powers of running appear to have played the same 

 part as isolation in islands and similarly the power of flight 

 has been lost. In a few others the reason is obscure. 



The class has to be divided into two sub-classes to 

 allow the inclusion of the remarkable fossil known as 

 Archceopteryx. 



Sub-Class I. — Arch.eornithes. 



Archceopteryx lithographica is a fossil animal found in 

 the Jurassic strata of Solenhofen (Bavaria). Its extreme 

 interest lies in the evidence it furnishes of the descent of 

 birds from reptiles. It was about the size of a crow, and 

 was apparently completely clothed in feathers of a similar 

 type to those of modern birds. It had small homodont 

 teeth in both jaws, and the vertebral column apparently 

 consisted of free vertebrae throughout, including a very long 

 tail, each caudal vertebra bearing a pair of rectrices. The 

 fore-limb had three digits, as in modern birds, but the 

 metacarpals are said to have been free, and the digits had the 

 full complement of phalanges (2, 3 and 4) terminating in a 

 claw. There w^as a large number of ribs, and the so- 

 called "abdominal ribs" found in many reptiles were also 

 present. The pelvis and hind-limbs appear to have differed 

 little from those of modern birds. From the proportions of 

 the body it is questionable whether Archceopteryx was bipedal ; 

 it probably used all four limbs (when not flying) in a terrestrial 

 or more probably an arboreal mode of locomotion. 



Sub-Class II. — Neornithes. 



This sub-class includes all the modern birds, of which the 

 general characters have been enumerated. 



M. 30 



