14 ODONTORNITHES. 



The teeth were evidently held in position by cartilage, which permitted 

 some fore and aft movement ; but lateral motion was much restricted by 

 the depth and narrowness of the groove, and the large size of the fangs. 

 "With the decay of this cartilage after death, the teeth readily lost their 

 erect position, and became more or less displaced. 



In the best preserved specimen of Eesperornis regalis (number 1206), 

 most of the teeth had fallen out of the grooves, when found, and were 

 lying scattered along beside the jaws, as often seen in specimens of 

 Ichthyosaurus. The embryonic sockets, in this specimen, indicate that 

 there were fourteen functional teeth in the maxillary bone, and thirty- 

 three teeth in the corresponding ramus of the lower jaw, as shown in 

 Plate I, figures 1-4. In Eesperornis crassipes (number 1474), a number 

 of teeth were likewise found in position in the jaws, but the exact number 

 originally in each could not be determined. 



The teeth of Eesperornis were gradually replaced by successional 

 teeth, and this took place in a manner very similar to that in some reptiles. 

 The germ of the young tooth was formed on the inner side of the fang of 

 the tooth in use, and, as it increased in size,, a pit for its reception was here 

 gradually made by absorption. The old tooth at last became undermined, 

 and was expelled by the new one, which occupied the same position, the 

 number of teeth thus remaining the same. 



The teeth of Hesperomis have conical pointed crowns, covered with 

 smooth enamel, and supported on stout fangs. In form of crown and base, 

 they closely resemble the teeth of Mosasauroid reptiles, one of which is 

 represented on page 15, figure 7, for comparison. The outer and inner 

 surfaces of the crown are separated by sharp ridges, which are without 

 serrations. The outer side is nearly ]:>lane, and the inner surface strongly 

 convex. 



The crowns of the teeth are mainly composed of firm dentine, invested 

 with a layer of enamel. The relative proportions of these are shown in 

 figure 4. The pulp cavity was large, and in the specimen above repre- 

 sented Avas filled with calcite. The coronal walls of this cavity are smooth, 

 and well defined. The fang consists of osteo-dentine. 



