636 MANUAL OF ZOOLOGY. 



11 um is without a keel, the wings are rudimentary, and the teeth 

 are implanted in a groove in the jaw and not in separate sockets. 



ORDER II. ODONTOTORM^E. This order has been founded 

 by Marsh for the reception of two remarkable birds, which he 

 has named Ichthyornis dispar and Apatornis celer, both from 

 the Cretaceous rocks of North America. 



In Ichthyornis dispar, which may be taken as the type of the 

 order, the teeth (fig. 352, a) were sunk in distinct sockets, and 

 were " small, compressed, and pointed, and all of those pre- 

 served are similar. Those in the lower jaw number about 

 twenty in each ramus, and are all more or less inclined back- 

 wards. . . . The maxillary teeth appear to have been 

 equally numerous, and essentially the same as those in the 

 mandible. The skull was of moderate size, and the eyes 

 placed well forward. The lower jaws are long and slender, 

 and the rami were not closely united at the symphysis. . . . 

 The jaws were apparently not encased in a horny sheath. 



" The scapular arch, and the bones of the wings and legs, 

 all conform closely to the true ornithic type. The wings were 

 large in proportion to the legs, and the humerus had an 

 extended radial crest. The metacarpals were united, as in 

 ordinary birds. The bones of the posterior extremities re- 

 semble those of swimming birds. The vertebrae (see fig. 352, 

 c and c') were all biconcave, the concavities at each end of 

 the centra being distinct and nearly alike. Whether the tail 

 was elongated cannot at present be determined ; but the last 

 vertebra of the sacrum was unusually large. 



"The bird was fully adult, and about as large as a pigeon. 

 With the exception of the skull, the bones do not appear to 

 have been pneumatic, though most of them are hollow. The 

 species was carnivorous, and probably aquatic." (Marsh.) 



Apatornis agrees with Ichthyornis in most of the above char- 

 acters, but the structure of its jaws is not fully known. It 

 follows from the above that the order Odontotormce is char- 

 acterised by the possession of distinct teeth sunk in separate 

 sockets in the jaw and not in a continuous groove, by the fact that 

 the vertebra are biconcave, and by the possession of a carinate 

 sternum and well-developed wings. 



LITERATURE. 



[In addition to many of the works mentioned in the list of treatises re- 

 lating to the Vertebrata in general, the following are some of the more im- 

 portant sources of information as to recent and fossil Birds : ] 



i. Article "Aves." Owen. 'Todd's Cyclopaedia of Anat. and Phys.' 

 1836. 



