84 O. C. Marsh — The Skull and Brain of Claosaurus. 



Seen from above (Plate IY, figure 3, and Plate V, figure 5), 

 the structure of the skull itself is shown to the best advantage. 

 In front are the large premaxillaries, deeply excavated for the 

 nasal openings. These bones are separate, and each sends 

 back a long, slender process inside the anterior projection of 

 the nasal, and a still longer process forming the lower border 

 of the narial orifice, and extending to the lachrymal. The 

 front of the premaxillaries is especially massive, and its sur- 

 face rugose, indicating that it had been covered with a horny 

 beak. The lower border is sharp, conforming to the corre- 

 sponding surface of the predentary bone, which was doubtless 

 also enclosed in a horny covering. The premaxillaries were 

 entirely without teeth. 



The nasal bones are long and slender, and especially pro- 

 duced in front, where they embrace the posterior median 

 extensions of the premaxillaries. They also meet the lateral 

 processes of the premaxillaries behind the nasal openings, and 

 likewise touch the lachrymals. Further back, they meet the 

 prefrontals, and closely unite with the frontals, as shown in 

 Plate IY, figure 3. 



The frontal bones are quite short, and nearly as wide as 

 long. They are united to each other by a well-marked suture. 

 Their upper surface is smooth, and there is a slight depression 

 on either side, posterior to the suture with the prefrontals. 

 Each frontal bone forms a portion of the upper border of the 

 orbit, and behind this meets the postfrontal. Posteriorly, the 

 frontals form the anterior border of the supra-temporal fossae, 

 and between these unite by suture with the coossified parietals. 



The latter bones are quite small, and appear on the upper 

 surface of the skull mainly as a narrow ridge separating the 

 supra-temporal fossae, and ending behind in a point, between 

 the median processes of the squamosals. The parietals expand 

 below, where they cover the posterior portion of the brain- 

 cavity. 



The squamosal bones are robust, and their position and con- 

 nections are well shown on Plate IY, figures 1 and 3. On 

 the median line above, they meet the narrow extension of the 

 parietals, and exterior to this, they form the posterior borders 

 of the supra-temporal fossae. In front, they unite by a strong 

 process with the posterior branch of the postfrontals. Their 

 posterior border is joined mainly to the exoccipitals. On the 

 outer surface of each squamosal, there is a deep pit to receive 

 the head of the quadrate, and in front of this, a short narrow 

 process extends down the quadrate, forming a part of the 

 border of the infra-temporal fossa. * 



The quadrate bone and its main connections are shown on 

 Plate IY, figures 1-3. It is firmly supported above by the 



