RESTORATION OP ICHTHTORNIS. 179 



If, now, we consider the skull of IcMhyomis, we find the avian and 

 the reptilian characters strangely blended. The teeth are evidently a 

 strong reptilian feature, and, before the discovery of IcMhyomis, were 

 entirely unknown in the class of Birds. Their method of implantation in 

 distinct sockets is a specialized character in reptiles, and was not shared 

 even by Hesperornis, the contemporary of IcMhyomis. The diminutive 

 elongated brain, also, points back to the reptiles. Other features of 

 the skull, for example, the single headed quadrate, are shared only by the 

 most reptilian of birds. The union of the lower jaws in front, by ligament 

 only, is characteristic of many reptiles, and is seen in Hesperornis, but is 

 unknown in all other birds. 1 The form of the skull and the obliteration of 

 most of the cranial sutures are points of resemblance to many modern birds. 



The locomotive organs of IcMhyomis are so similar to those of typical 

 birds that they present no such interesting mechanical problems as were 

 suggested by the skeleton of Hesperornis. In the vertebrae, however, we 

 find a primitive form retained, and also have the key to the origin of 

 one remarkable character in recent birds, which has hitherto remained 

 unexplained. 



While all existing birds, and all of the extinct forms so far as 

 known, including Hesperornis, have the peculiar saddle-shaped vertebrae, 

 those of IcMhyomis, and its near ally Apatomis, are biconcave. This fomi 

 is seen in a few recent and in many extinct Reptiles, and in the 

 Amphibians; but it is especially characteristic of Fishes, from which class 

 it was undoubtedly inherited by the superior groups. This character 

 alone indicates unmistakably a great antiquity for the class of birds. 



The saddle-shaped vertebrae are certainly one of the most marked 

 features in the skeleton of modern birds. This form is so peculiar and 

 so constant that it has been considered by many anatomists as the best 

 distinctive character for the class. In no other group of animals known do 

 we find the true saddle-shaped articulation of the centra seen in the 

 vertebra? of birds. 2 



' In the Pelicans and Curlews, the rami unite late by ankylosis. 



2 An approach to this form is shown in the cervical vertebrae of the Kangaroos. 



