Fig. 4. — Front view of the skull of B. 

 longus (one-sixth nat. size). 



102 Prof. 0. C. Marsh — A Neiv American Jurassic Dinosaur. 



The premaxillaries (Fig. 4) are narrow below, and with, the as- 

 cending processes very slender and 

 elongate. Along the median line 

 these processes form an obtuse 

 ridge, and above they project into 

 the nasal opening. Each pre- 

 maxillary contains four functional 

 teeth. 



The maxillaries are very largely 

 developed, more so than in most 

 other Isnown reptiles. The denti- 

 gerous portion is very high, and 

 slopes inward. The ascending pro- 

 cess is very long, thin and flattened, 

 inclosing near its base an oval 

 foramen, and leaving a large un- 

 ossified space posteriorly. Above, 

 it meets the nasal and prefrontal 

 bones. Along its inner border for 

 nearly its whole length, it unites 

 with the ascending process of the 

 premaxillary. Each maxillary con- 

 tains nine teeth, all situated in the 

 anterior part of the bone (Fig. 1). 



Along their upper margin, on the inner surface, the maxillaries 

 send off a thickened ridge or process, which meets its fellow, thus 

 excluding the premaxillaries from the palate. Above this, for a large 

 part of their length, the ascending processes of the maxillaries under- 

 lap the ascending processes of the premaxillaries, and join each other 

 on the median line. 



The orbits are situated posteriorly in the skull (Fig. 1), being 

 nearly over the articulation of the lower jaw. They are of medium 

 size, nearly circular in outline, their plane looking outward and 

 slightly backward. No indications of sclerotic plates have been found 

 either in Biplodocus or the other genera of Sauropoda. 



The supra-tempoi'al fossa is small, oval in outline, and directed 

 upwards and outwards. The lateral temporal fossa is elongated, and 

 oblique in position, bounded, both above and below, by rather slender 

 temporal bars. 



The pre-frontal and lachrymal bones are both small, the suture 

 connecting them, and also that uniting the latter with the jugal, 

 cannot be determined with certainty. 



The post-frontals are tri- radiate bones. The longest and most 

 slender branch is that descending downward and forward for connec- 

 tion with the jugal ; the shortest is the triangular projection directed 

 backward, and fitting into a groove of the squamosal ; the anterior 

 branch, which is thickened and rugose, forms part of the orbital 

 border above. 



Tha squamosal lies upon the upper border of the par-occipital 

 process. The lower portion is thin, and closely fitted over the head 

 of the quadrate. 



