Frof. 0. C. Marsh— On Birds ivith Teeth. 51 



maxillary grooves do not extend into tlie premaxillaries, and tlie 

 latter do not appear to have supported teeth. The external appear- 

 ance, moreover, of the premaxillaries seems to indicate that these 

 bones were covered with a horny bill, as in modern birds. 



The lower jaws are long, and slender, and the rami were united 

 in front only by cartilage. The dentary bone has a deep groove 

 throughout its entire length, and in this, teeth were thickly planted, 

 as in the jaws of Ichthyosaurus. The lower teeth are similar to 

 those above, and all were more or less recurved. (Plate II. Figure 5.) 

 These grooves contain slight projections from the sides, but there 

 are no true sockets. (Plate II. Figure 6.) 



The scapular arch of Hesperornis presents many features of in- 

 terest. The sternum is thin and weak, and entirely ivithout a keel. 

 In front, it resembles the sternum of Apteryx, but there are two 

 very deep posterior emarginations, as in the Penguins. The scapula 

 and coracoid are very small. The wing bones are diminutive, and 

 the wings were rudimentary, and useless as organs of either flight 

 or swimming. 



The vertebrae in the cervical and dorsal regions are of the true 

 ornithic type, the articular faces of the centra being quite as in 

 modern birds. (Plate II. Figures 7 and 8.) The sacrum is elongated, 

 and resembles that in recent diving birds. The last sacral vertebra 

 is quite small. The caudal vertebrse, which are about twelve in 

 number, are very peculiar, and indicate a structure not before seen 

 in birds. The anterior caudals are short, with high neural spines 

 and moderate transverse processes. The middle and posterior caudals 

 have very long and horizontally expanded transverse processes, 

 which restrict lateral motion, but clearly indicate that the tail was 

 moved vertically, probably in diving. The last three or four caudal 

 vertebrae are firmly coossified, forming a flat terminal mass, analo- 

 gous to, but quite unlike, the " ploughshare " bone of modern birds. 

 The anterior two at least of these caudals have expanded transverse 

 processes. 



The pelvic bones, although avian in type, are peculiar, and present 

 some well-marked reptilian features. A resemblance to the corre- 

 sponding bones of a Cassowary is at once evident, especially in a 

 side view, as the ilium, ischium, and pubis all have their posterior 

 extremities separate. The two latter are slender, and also free back 

 of their union with the ilium at the acetabulum. The ischium is 

 spatulate at its distal end, and the pubis rodlike. The acetabulum 

 differs from that in all known birds, in being closed internally by 

 bone, except a foramen, that perforates the inner wall. 



The femur is unusually short and stout, much flattened antero- 

 posteriorly, and the shaft curved forward. It somewhat resembles 

 in form the femur of Colymhus torquatus, Brun., but the great trochan- 

 ter is proportionally much less developed in a fore-and-aft direction, 

 and the shaft is much more flattened. The tibia is straight and 

 elongated. Its proximal end has a moderately developed cnemial 

 process, with an obtuse apex. The epi-cnemial ridge is prominent, 

 and continued distally about one-half the length of the shaft. The 



