470 STRUCTURE AND CLASSIFICATION OF BIRDS 



These two genera comprise a number of ' small birds, 

 scarcely larger than a pigeon. In their powerful wings and 

 small legs and feet they remind one of the terns, and accord- 

 ing to present evidence they were aquatic birds of similar 

 life and habits.' 



The restoration of Ichthyornis given by MAESH has 

 been extensively copied in various works, in some of which 

 it would appear as if our knowledge of the osteology of the 

 species selected were greater than is really the case. It has 

 been made, for example, to show schizorhinal nostrils and a 

 pelvis constructed after the carinate type, with the ischia and 

 ilia fused. It is not known w T hether the skull was schizo- 

 rhinal, as only the calvarium and the lower jaw and a 

 fragment of the upper jaw have been discovered. The skull 

 has well-marked grooves for the supra-orbital glands ; the 

 quadrate, as stated in the definition, is single-headed, as in 

 Hespcroriiis and many Struthiones. The brain, like that of 

 Hesperoniis, is small, and the cerebellum is remarkably 

 large as compared with the hemispheres. The teeth of Ichthy- 

 ornis are implanted in distinct sockets. 



MARSH has remarked upon the close resemblance between 

 the lower jaw, with its teeth, and that of the smaller mosa- 

 sauroid reptiles. In Ichthyornis dis'par there are twenty- 

 one distinct sockets in each ramus of the jaw. I. victor had 

 the same number of teeth ; in I. anceps the teeth were more 

 numerous, and at the same time more slender. The jaws 

 were united, as in Hesperornis, by cartilage or ligament. 



The vertebra, as already mentioned, are amphiccelous ; 

 but an approach to the typical saddle-shaped vertebrae is 

 seen in some of them. The atlas is notched for the odontoid 

 process of the axis. None of the dorsal vertebra? appear to 

 have coalesced, and there is a pygostyle quite typical in form, 

 but rather small. The shoulder girdle of both Ichthijornis 

 and A'patornis is constructed upon the carinate plan. 1 There 

 is the same angle between the scapula and the coracoid, and 

 the clavicles are well developed. There are, however, differ- 



1 SHOFELDT (' Notes on the Extinct Bird Iclitliyornis,'' J. Anat. Phys. xxvii. 

 p. 336) especially compares Iclitliyornis with Ehyncliops and Sterna. 



