PROTOCERA TOPS ANDREWS! 



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The lacryma] is an irregular-shaped bone forming the anterior limit of the orbit and containing 

 the upper half of the preorbital fossa. The Lacryma] is bounded by the nasal and prefrontal above, 

 the jugal behind and below, and the maxillary below and in front. The preorbital ( lacrymal) 

 foramen lies in the mid-length of its inferior border. 



The jugal is one of the largest bones of the skull. It is roughly quadrangular, with the 

 longest axis nearly horizontal. It is bounded in front by the maxillary and lacrymal, above by the 

 postorbital, and has a long process above the infratemporal fossa which meets the squamosal. Within, 

 the jugal bears upon the quadratojugal and quadrate. In skull No. 6429 A.M.N.H., a horizontal 

 ridge divides the posterior part of the jugal into an upper and lower portion. The rear lower part 

 of the jugal flares outward very strongly in some skulls of Protoceratops (sec PI. I), suggesting 



Fig. 33. — Dorsal view of skull of Protoceratofs andrewsi, ]/\ natural size. /, frontal; itf, infratemporal fossa; ;', jugal; 

 /.lacrymal; mx, maxillary; «, nasal; nar, narial opening; o, orbit; p, parietal; fa, palpebral; ff, parietal fenestra; fmx, 

 premaxillary; fo, postfrontal; prj, prefrontal; qj, quadratojugal; r, rostral; sq, squamosal; s/f, supratemporal fossa. 



somewhat the jugal horns of Pentacerato-ps. There is no trace, however, of an epi jugal bone, 

 although the surface of the jugal is in places somewhat rugose and pitted. 



The postfrontal (postorbital) is bounded by the prefrontal and the supratemporal fossa above, 

 the rear of the orbit and the squamosal laterally, and the jugal below. 



The crest is composed of the usual three elements of which the unpaired median one is gener- 

 ally considered as the fused parietals. The skull of Protoceratops, with its primitive simplicity, 

 affords the best of evidence for this interpretation. In this, Gregory and Mook agree. The lateral 

 elements are of course the squamosals; concerning these, opinion is undivided. The latter bones lie 

 in their usual position bounding the parietals on their outer anterior margins. Anteriorly, the 

 squamosal articulates with the postfrontal and the extended process of the jugal, while its lower 

 margin meets the quadratojugal and quadrate, which combine to form the infratemporal arcade and, 

 together with the jugal and squamosal, enclose the very large infratemporal fossa. The squamosals 

 bear slight vascular impressions on the outer surface. The parietal bones are broadly expanded, 

 completely surround the large, slightly irregular fenestrae, and form the periphery of the crest 

 beyond the limits of the squamosals. They are peculiar in having the midline raised into a pro- 

 nounced sagittal crest. Anteriorly, their surface, together with that of part of each squamosal, dips 

 below the general level of the surface of the crest, especially in the wake of the supratemporal fossae. 

 Such depressed areas are always present in varying degree among Ceratopsia, especially in Chasmo- 

 saurus, but never to the relative extent seen in Protoceratops. They seem to be the areas of origin of 

 the temporal muscles which, passing downward and slightly forward beneath the postfrontal and 

 jugal bones, were finally inserted into the coronoid process of the jaw and served to actuate that 

 powerful member. Here the pull is more directly upward than in later Ceratopsia and as a conse- 

 quence the coronoid process of the jaw has a different shape from that of Triceratops or Monoclonins 

 (Centrosaurus), for instance. 



