420 0. C. Marsh — Characters of the Ceratopsidce. 



The teeth in this family are entirely confined to the 

 maxillary and dentary bones. The rostral bone, the premax- 

 illaries, and the pre-dentary, are entirely edentulous. 



Cervical Vertebrce. 



The atlas and axis of Triceratops are coossified with each 

 other, and at least one other vertebra is firmly united with 

 them. These form a solid mass, well adapted to support the 

 enormous head. 



The cup for the occipital condyle is nearly round, and very 

 deep, as shown in Plate VI, fig. 6, a. In fig. 5, the same speci- 

 men is shown, seen from the side, with the fourth vertebra in 

 position, but free. In this specimen, the rib of the second ver- 

 tebra is coossified with it. On the fourth vertebra, the rib had 

 a free articulation. 



Scapular Arch and Limbs. 



The scapula is massive, especially below. The shaft is nar- 

 row, sigmoid above, with a thin edge in front, and very thick 

 posterior margin. 



The humerus is large and robust, and similar in form to 

 that of Stegosaurus. It is nearly as long as the femur in one 

 individual, proving that the animal walked on all four feet. 

 The radius and ulna are comparatively short and stout, and the 

 latter has a very large olecranon process. The digits were 

 terminated by broad hoof-like phalanges, one of which is 

 shown on Plate VI, figures 7-9. 



The femur is short, with the great trochanter well developed. 

 The shaft is comparatively slender, and the distal end much 

 expanded. The tibia is of moderate length, and resembles that 

 of Stegosaurus. In one individual, at least, the astragalus is 

 firmly coossified with the distal end. of the tibia, as in Stego- 

 saurus. The limb bones and other parts of the skeleton are 

 nearly or quite solid. 



The Pelvis. 



The pelvis in this group is very characteristic, and the three 

 bones, ilium, ischium, and pubis, all take a prominent part*in 

 forming the acetabulum. The relative size and position of" 

 these are shown in Plate VII, fig. 1, which represents the 

 pelvic elements as nearly in the same plane as their form 

 will allow, while retaining essentially their relative position in 

 life. 



The ilium is much elongated, and differs widely from that in 

 any of the known groups of the Dinosauria. The portion in 



