10 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 60. 



Fig. 8. — Articulated left 

 postfrontal and post- 

 ORBITAL BONES OF Sa- 

 NIWA ENSIDENS LeIDY. 



Type, Cat. No. 2185, 

 U.S.N.M. Natural size. 



P, cupped border FOR 

 ARTICULATION WITH PA- 

 RIETAL AND FRONTAL I 

 PO, POSTORBITAL ; ptf, 

 POSTFRONTAL. 



Postorhital. — Both postorbital bones are present, the left articu- 

 lated with the postfrontal, the ri^ht detached. The latter has an 

 expanded anterior end which articulates with the postfrontal by a 

 cupped articular surface developed on the upper anterior border. In 

 position it extends downward below the postfrontal as a pointed 

 process (see fig. 8), but apparently not reaching the jugal. Extend- 

 ing posteriorly the postfrontal develops a 

 slender tapering process which articulated 

 with the squamosal, thus forming the supra- 

 temporal arcade as in other members of the 

 Varanidae. 



Prootic. — The left prootic was found at- 

 tached by matrix to the left exoccipital, but 

 slightly displaced from its proper articulation 

 with that element (see fig. 9). It closely re- 

 sembles the corresponding bone in Varanus 

 salvator, being a curved bone having a nar- 

 rowed posterior half that laps along the upper 

 anterior side of the paraoccipital process by 

 squamous suture, and a flattened broader anterior half that turns 

 upward from the horizontal at an angle of 45° to meet the parietal 

 on the external side at about the middle of the supratemporal fossa. 

 The inner posterior border forms a junction with the supraoccipital, 

 exoccipital, and opisthotic. The inner surface of this flattened end 

 contributes to the formation of the lateral wall of the brain cavitj'^ 

 and to the boundary to the auditory capsule. The ventral process, 

 which in Varanus extends forward and 

 downward to articulate with the basiphe- 

 noid, is missing in the fossil, but presumably 

 it will be found to be much like that of 

 Varanus. 



Prefrontal. — The left prefrontal was found 

 in the matrix but little disturbed from its 

 proper articulation with the underlying 

 bones of the palate. It is an irregularly- 

 shaped bone (see fig. 10) that forms the 

 greater part of the anterior boundary of the 

 orbit and contributes to both the dorsal and 

 lateral surfaces of the skull. Internally it also develops a partial 

 postlateral wall for the rhineocephalic chamber. The contribution 

 to the dorsal surface is of considerably greater extent, both trans- 

 versel}^ and anteroposteriorly, than in a Varanus skull of equal di- 

 mensions. Posteriorly a tapering process extends backward along 

 the outer edge of the frontal, which, as in Varanus, probably termi- 



■ exo. 



Fig. 9. — Left prootic at- 

 tached TO EXOCCIPITAL OF 

 SAME SIDE OF SANIWA EN- 

 SIDENS Lbidy. Type, Cat. 

 No. 2185, U.S.N.M. Nat 

 URAL SIZE. Later A I 



VIEW. eXOj EXOCCIPITAL; 



pro, proOtic. 



