m 



212 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



extremities of the post- and prefrontals on the external border con- 

 tributes to the inner boundary of the supraorbital fossa, but to no 

 such extent as shown in Plate 53, fig. 2, in "Dinosaurs of North 

 America." The orbital surface is large and concave antero-pos- 

 teriorly in Cat. No. 5473, U.S.N.M., being separated from that of the 

 opposite side b}^ an intermediate space of 30 mm. The internal 

 median ventral surface is separated from the orbital surface by an 

 irregular, longitudinal ridge. This internal surface constitutes the 

 roof of the anterior part of the brain case for the reception of the 

 olfactory lobes. 



Post frontal. — The postfrontal is a three-rayed bone, and resembles 

 that of the Monitor most nearly, but its union is chiefly with the 

 frontals. One short, heavy ray articulates with the postero-external 

 angle of the frontal and forms part of the anterior boundary of the 

 supratemporal fossa. A slender, posteriorly directed ray articulates 

 by a long, lapping suture with the anterior branch of the squamosal 

 pnd with that bone completes the upper temporal bar which forms the 

 outer boundary of the supratemporal fossa. The third ray, the long- 

 est of the three, unites by its strong descending process with the jugal 

 and thus forms the posterior border of the orbit. This process below 

 is trihedral in cross section. 



Prefrontal. — The presence of a prefrontal is plainly indicated in 

 two specimens in Yale Museum, Nos. 1880 and 1887. It is the lower 

 external surface of this bone which gives the main support to the 

 supraorbital and its posterior outer border forms a part of the inter- 

 nal boundary of the supraorbital fossa. This element, as preserved 

 in the above specimens, is too mutilated for detailed description. 



Quadrate. — I quote the following description from Professor 

 Marsh's unpublished notes, kindlj^ placed at my disposal by Prof. 

 R. S. Lull, of Yale University Museum : 



The quadnite resembles most nearly that of Iguana Ijut more slender. From 

 the side the posterior border is concave and above the middle is rather thin. 

 The posterior " hamalar " process of the head is quite thin. The surface for 

 the pterygoid is larjre and hollowed and formed by thin bone. The articulation 

 for the jaw is rectangular in outline and but slightly convex. From the front 

 it is concave transversely throughout its whole length, deeply above, more 

 shallow below. 



Plate 9, fig. 2, shows the long, finger-like process of the pterygoid 

 which extends backward and laps along a thin, forwardly directed 

 process on the inner surface of the lower part of the quadrate. The 

 quadrate in the skull of C inedius, No. 1880, Yale Museum, is 115 

 mm. in length. The external view of this bone is well shown in fig. 

 2, qu. In Camptosaurus the quadrate is more curved and lighter than 

 the corresponding element in Iguanodon. 



Quadrato'jugal. — The presence of this element is plainly indicated 

 in specimen No. 1887, Yale University Museum (see Plate 8, q}). 



