SUB-CLASS II ORNITHURAE 265 



British and the other in the Berlin Museum. They are considered as repre- 

 senting two species, A. macrura and A. siemensi, and fortunately supplement 

 each other in such wise that the osteology is known with tolerable accui'acy. 

 Contrary to the usual condition among birds, none of the bones appear to 

 have been pneumatic. 



The skull is shaped like that of a typical bird, its constituent elements 

 being fused together, and the quadrate apparently free. A sclerotic ring is 

 present, and there is a series of thirteen conical teeth on each side in the upper 

 jaw, fixed probably in distinct sockets. The vertebral column comprises 

 about fifty vertebrae, of which ten or eleven are cervical, eleven or twelve 

 dorsal, two lumbar, six or seven sacral, and about twenty caudal. The 

 cervical and dorsal vertebrae seem to have been amphicoelous, or amphi- 

 platyan, as in reptiles, and bear weakly developed transverse processes and 

 neural spines. The ribs are veiy slender, free in the neck region, and without 

 ossified uncinate processes in the thoracic region. Twelve or thirteen pairs of 

 abdominal ribs are present in the ventral wall of the body cavity. In the 

 jDectoral arch the long and slender scapula is essentially bird-like, and exhibits 

 a well-developed acromion. The sternum is unfortunately not well preserved, 

 but the coracoids and U-shaped furcula resemble those of modern Carinate 

 birds. The wing is relatively small, and its bones slender. Radius and ulna 

 are straight, and but little shorter than the humerus. The carpus is im- 

 perfectly known, and the three metacarpals appear to have been free. Meta- 

 carpal No. I is quite short, and No. ii longer and stouter than the first or 

 third. The lizard-like manus terminates in three clawed digits having the 

 phalangeal formula 2, 3, 4. 



The three pelvic elements appear to have been distinct, and united with 

 each other by persistent sutures. The acetabulum is perforate. The hind- 

 limb is essentially avian, and conspicuous only for the weak development of 

 the cnemial crest of the tibia. There are four clawed digits in the pes (Nos. I 

 to iv), with the phalangeal formula 2, 3, 4, 5. In the wing are observed 

 seven primary and ten secondary remiges with their coverts. The rectrices of 

 the tail are arranged in pairs, directed obliquely backward, one pair to each 

 vertebra. Contour feathers are also indicated on the neck and along the 

 tibia. 



Archaeojjteryx appears to have been intermediate in size between an ordinary 

 pigeon and crow, and to have enjoyed a moderate power of flight. The claAved 

 digits of the manus were doubtless effective in climbing trees and rocks. In 

 this connection the quadrupedal habits of young modern birds, especially the 

 hoactzin (Ojnsthocomiis), cormorant, and certain water-fowls, are of significance 

 as indicating a possible survival, "handed down from the very dawn of avian 

 development " (Py craft). 



Sub-Class 2. ORNITHURAE. 



Tail feathers arranged like a fan around the terminal portion of the shortened 

 caudal vertebrae, a nuniber of which are usually united to form, a pygostyle. Sternum 

 well developed; dorsal ribs (save in Palamedea and Chauna) with uncinate 

 processes; cerviccd ribs united with their vertebrae. Pelvic elements proximally 

 united ; metacarpals united. 



