232 AVES. 



still so few, that the stages in the process are as yet only very 

 imperfectly traceable. 



Sub-Class 1. Archaeornithes. 

 ORDER 1. SAURUR^E. 



The primitive " lizard-tailed " birds are only definitely 

 known by two fine examples of one genus (Archceopteryx) from 

 the Upper Jurassic of Bavaria. They are preserved in slabs of 

 Lithographic Stone, which is capable of retaining the most 

 delicate impressions and thus displays even the feathers. 



FIG. 141. 



Archaeopteryx macrura; skull and mandible, right lateral aspect, nat. size. 

 U. Jurassic (Lithographic Stone) ; Bavaria. (After Dames.) 



Archaeopteryx (figs. 141, 142). The skull is shaped like that of a 

 typical bird, the brain-case being relatively large, is constituent elements 

 fused together, and the quadrate apparently free. Sclerotic plates are 

 observable. There is a regular series of conical teeth, these probably 

 fixed in distinct sockets. The vertebral column comprises about 50 ver- 

 tebrae, of which 10 or 11 belong to the neck, 11 or 12 to the dorsal region, 

 2 to the lumbar region, 6 or 7 to the sacrum, and about 20 to the tail. The 

 vertebral centra seem to have been either amphicoelous or with flat ends. 

 The ribs are very slender, free in the cervical region, and not bearing 

 ossified uncinate processes in the thoracic region. The sternum is not 

 satisfactorily known, but the U-shaped furcula resembles that of modern 

 Carinate birds. The wing is relatively small, and exhibits three digits 

 (nos. i to in), each terminating in a claw ; the phalangeal formula is 

 2, 3, 4. It is not quite certain whether the metacarpals were fused 

 together, and the carpus is still too imperfectly known for discussion. 

 In the pelvis, the ilium is considerably extended forwards and backwards, 

 while the acetabulum is perforate; the sutures between the elements 

 were probably persistent. The hind limb is essentially avian, only re- 

 markable for the unusually small development of the cnemial crest on the 



