BIRDS WITH TEETH. 



25 



The skull was very large in proportion to the rest of the skeleton, the dispropor- 

 tion being well shown in the accompanying cut, Fig. 9. The cranial sutures were 

 nearly obliterated. The quadrate bone, as shown in Fig. 8, has only a single facet on 

 its articular head, agreeing in that respect with Hesperornis and the Struthionine 

 birds. The brain was small, and, like that of Hesperornis, which it resembles more 

 nearly than that of any other known bird, in its main features strongly reptilian, as in 

 the elongated form and the prominent optic lobes. The two rami of the lower jaw 

 were entirely separate, 

 having been united in 

 front only by cartilage, 

 and the tooth-bearing 

 portion is so similar to 

 that of some of the smal- 

 ler Mosasauroid reptiles that, 

 without other portions of the skel- 

 eton, the two could hardly be dis- 

 tinguished. The teeth were im- 

 planted in distinct sockets, thus 

 differing widely from what was 

 the case in Hesperornis; they 

 were all sharp, pointed, and 

 strongly recurved, those of the 

 upper jaw apparently larger than 

 the lower ones. Whether the an- 

 terior portion of the upper jaw, 

 the premaxilla, contained teeth is 

 uncertain, but Professor Marsh 

 thinks it probable that they were 

 absent, as in Hesperornis. The 

 whole surface of the tooth above 

 the jaw was covered with smooth 

 enamel. The succession of the 

 teeth took place vertically, as in 

 crocodiles and Dinosaurs, and not 

 laterally, as in Hesperornis and 

 the Mosasaurs. The young teeth 

 were much inclined when they 

 first appeared above the jaw, after 

 the old teeth had been expelled. 



The presacral vertebrae were more remarkable than those of any other known bird 

 except Archceopteryx, for they were not saddle-shaped, but biconcave as shown in Figs. 

 10, 11, which show clearly the cup-shaped articulation of the centrum. However, the 

 third vertebra of the neck, but no other, presents a modified form (Fig. 12), evidently 

 produced by the necessity of providing for an easy vertical motion of the neck at its 

 first bend. The tail is remarkable for being of the same type as is that of all mod- 

 ern birds, namely, comparatively short, and the last vertebras anchylosed into a 

 pygostyle. 



The fore extremities, including the shoulder girdle, were, so far as known, essen- 



FIG. 9. Restoration of Ichthyornis. 



