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LIFE : OUTLINES OF GENERAL BIOLOGY 



developed in the crocodile and Sphenodon, as also in many extinct 

 reptiles. They are interesting structures, developing apart from the 

 main skeleton, as cutaneous ossifications across the ventral wall of 

 the abdomen. 



The breastbone is at most vaguely preserved, and the same must 

 be said of the merry- thought. Of the rest of the pectoral girdle it 

 is stated by Petronievicz and Smith Woodward that "although 

 Archaeopteryx was obviously a bird of flight, its scapulo-coracoid 



Fig. 153. 



Bittern, Botaurus stellaris. From a specimen. Standing erect among the 

 reeds, with upraised head, the bird well illustrates cryptic coloration. 

 It has a cloak of invisibility. 



is more closely similar to that of certain Mesozoic reptiles than that 

 of any other known bird". 



The wing of Archaeopteryx is in a very interesting phase — inter- 

 mediate between reptilian and avian fore-limbs. In an ordinary 

 flying bird there is a reduction of digits to the first three, a fusion of 

 half of the wrist or carpal bones with all the three metacarpals to 

 form a firm basis (carpometacarpus) for the longest flight-feathers 

 {the primaries) ; the free carpal bones are reduced to two, and in 

 most cases there are no claws. In a number of birds there is a claw 

 on the thumb; in rare cases (e.g. ostrich) there is another on the 

 second digit ; in the young South American Hoatzin or Opisthocomus 



