OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



21 



In front of the superior process the concave upper border contributes to the 

 boundary of the narial opening and to a considerably greater degree than in 

 Ceratosaurus. 



Posterior to the base of the ascending process the maxillary narrows rapidly 

 in width to the obtusely pointed posterior end, which underlaps and unites by 

 squamous suture with the anterior end of the jugal. 



Viewed from the side the dental border is slightly sinuous. The lower 

 external surface is perforated by a considerable number of foramina. The larger 

 foramina appear to arrange themselves in two rows, an upper curved row that in 

 going forward ascends one- third the height of the bone, and a lower row that parallels 

 the alveolar border (fig. 2, pi. 4). Between these rows, and irregularly placed, are 

 numerous smaller foramina, and forward of the curved row, which stops beneath 

 the second antiorbital fenestra, scattered foramina are observed nearly to the top 

 of this portion of the maxillary. 



-TICZ 



Fig. 12.— Left maxillary of Antrodemus valens Leidt. No. 4734, U.S.N.M. Internal view. § nat. size. /", Second 

 antiorbital fenestra; gr, grooves for blood vessels; na, extent of union with nasal bone; pmx, end joining 



PREMAXILLART. 



The general form and appearance of the maxillary when detached from the sur- 

 rounding elements is well shown in figure 12. 



On the internal side (fig. 12) some 25 mm., superior to the aveolar border on 

 the anterior end and approaching withing 5 mm. at the posterior end, is a row of 

 small dental foramina. These foramina are at the bases of the interdental plates 

 and are connected by nutrient grooves (gr, fig. 12). The interdental plates have 

 their internal surfaces considerably roughened, and they shorten dorso-ventrally 

 from the front toward the back. On the upper border of the internal side, on the 

 anterior half of the maxillary, a strong shelf of bone projects inward, the anterior 

 end of this shelf projecting some distance in front of the maxillo-premaxillary 

 144035—20 3 



