76 



THE CERATOPSIA. 



sacrals, and all the succeeding sacral ribs spring from the point of union of the succeeding 

 centra except the last, which is given off directly from the middle of the centrum of the tenth 

 sacral; while the next preceding springs jointly from the eighth and ninth centra, it is for the 

 most part borne by the ninth. The diapophyses of the first and second vertebras are short and 

 weak, much more so than in Triceratops, and are without inferior plates. Those of the suc- 

 ceeding vertebras are longer, stouter, much expanded superiorly, while inferiorly they are 

 united throughout their length with the corresponding sacral ribs by thin, bony plates, which 

 in the region of the acetabulum give a firm support to the longitudinal bar mentioned above, 

 formed by the expansion and union of the extremities of the sacral ribs of this region and 

 constituting a portion of the wall of the acetabulum. This bar, together with the coalesced 

 sacral ribs and diapophyses, incloses three foramina which are left open both above and below. 

 Next to the skull the most important distinctive characters in the Ceratopsidas are to be 

 found in the sacrum. It is unfortunate that as yet the best sacra have been found either 

 isolated or at most associated with only fragmentary or indifferent skull material, so that for 

 the most part it has been difficult to correlate the various forms of sacra and crania. The 

 same may be said of the present specimen, for although Cope in his description has referred 

 it to the same skeleton with the parietals and postfrontal described above, there would seem 



from such general characters as size, color, degree 

 of petrifaction, etc., to be little doubt that all 

 three pertained to as many different individuals. 

 Moreover, associated with them in the same lot 

 (designated Lot II by Cope) are representatives 

 of many different individuals pertaining not only 

 to various species, but to genera, families, orders, 

 and even classes of reptiles, and almost without 

 exception unaccompanied by any distinctive 

 marks or labels giving data as to their association 

 or as to the geological horizon or geographical 

 position in which they were found, other than the 

 Judith River beds of Montana. 



The cervicals. " — Only the three [four] 6 an- 

 terior cervicals are known. The three coalesced 

 vertebras described by Cope as anterior dorsals 

 are in reality the atlas, axis, and third [and 

 fourth] cervical. All of these [except the atlas] 

 bore double-headed cervical ribs. They are 

 firmly coossified by their centra. The atlas [and axis] has the lateral and vertical diameters 

 nearly equal, it bears no spine, and at its anterior extremity there is a deep cup for the reception 

 of the condyle of the skull. The vertical diameter of the second [third] and third [fourth] 

 cervicals exceeds the transverse, although in the present specimen the proportions have 

 evidently been much altered by crushing. Both these vertebras bear spines, and that of the 

 axis [third cervical] is much extended antero-posteriorly. These spines are closely applied to 

 one another, though not coossified, save at the base, where they are separated by a large 

 circular foramen 28 millimeters in diameter. 



The dorsals. — There are in the collection a number of dorsals, all incomplete and evidently 

 found isolated, and there is at present no record available as to their associations. In size 



a The coalesced anterior cervicals of Monodonius crassus, as in Triceratops, undoubtedly consist of four bones, the atlas being reduced 

 to a narrow ring-like element, the line of demarcation being indicated by a series of pit-like depressions ranging from the inferior surface of 

 the bone upward and fading out a little beyond the mid-distance to the summit. The fore and aft diameter of the atlas as thus indicated 

 is much greater inferiorly. 



i Numbers in brackets added by R. S. Lull. 



c Fig. 78 as prepared under Mr. Hatcher's direction failed to indicate these depressions. The drawing has been subsequently corrected 

 to agree with the specimen. The axis, Hatcher's atlas, is rendered thus somewhat less in anterior extent, though its posterior limitations 

 are as before. The anterior margin of the spine, which rises abruptly above the suture between the axis and the third cervical, extends 

 forward in a gentle curve fading out on the dorsal portion of the axis. The axis also bears two distinct rib facets as indicated in the 

 figure. Herein it differs from that of Triceratops, in which no ribs are borne in the axis. (Compare fig. 50, p. 47.) — R. S. L. 



II III IV 



Fig. 78. — Atlas, axis, and third and fourth cervical of type of 

 Monodonius crassus Cope (No. 3998, American Museum of 

 Natural History), as seen from left side, a, Anterior end; 

 p, posterior. One-fourth natural size. (Drawing altered 

 under the direction of R. S. Lull.)c 



