40 BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



Measurements of lower jaw of Stegosaurus stenops, No. 4934. Type. 



Greatest length 388 



Distance between posterior extremities of rami 179 



Width, across anterior extremities of rami „. . , 63 



Height of ramus below center of orbit .„ 75 



Height of ramus below posterior border of narial opening 41 



Width of predentary, estimated 64 



Hyoid. — That Stegosaurus had a well developed hyoid is clearly shown by speci- 

 men No. 4935 in the National Museum, which has the thyrohyals of both sides 



preserved as shown in 



-or figure 9. The better 



preserved element is 



a long, flattened, 



slightly curved bar of 



bone. Comparing it 



with the thyiohyal of 



Carnptosaurus which 



was found in situ,^ the 



/^\ ^-^-^^^^^^^^^^P^ ^^^^^^^^^\ expanded end prob- 



"^ ^^ ably represents the 



Fig. 9. — Thteoht.\ls op Stegosaurus sp. Cat. no. 4935, U.S.N.M. J Nat. size. lOrWard extremity. 

 Relation.^ shown as FOxraD in the matrix, o, o, Anterior ends; p, po-sterioe Sixty-eight miHime- 



^^""' ters posterior to this 



end, the bone reaches its maximum width of 19 mm. From this point it gradually 

 narrows in both directions. Posteriorly it tapers to a small, smooth, rounded end. 

 Dr. F. A. Lucas, in an impubUshed manuscript, obsei-ves "that judging from their 

 length it seems probable that these reptiles were provided with extensile tongues." 

 The principal measurements are as follows : 



Greatest length 174 



Greatest width of anterior end 18 



Greatest width of posterior end 7 



External Openings in the Skull. 



Supratem'poral fossae (e.). — The irregularly rounded supraoccipital openings 

 situated one on either side of the parietals are comparatively small ia Stegosaurus. 

 In S. stenops these fossae are bouaded anteriorly by an inner branch of the post- 

 orbitals and the outwardly curved ends of the parietals. In skull No. 4936, identi- 

 fied by Marsh as S. armatus, the frontal also contributes to this boundary (fig. 1, 

 pi. 10). Internally the boundary Js formed by the parietals, posteriorly by pro- 

 cesses from the parietals and squamosals which meet at the posterior center of the 

 opening, externally by branches of the postorbital and squamosal. 



Infratemporal fossae (c). — The infratemporal fossae are vertically elongate, 

 openiags with their greatest diameter inclined at an angle of 45° to the longer axes 

 of the skull (c, pi. 5). These fossae are bounded above by the postemporal bar 

 formed by processes of the postorbital and squamosal bones; anteriorly by the 



' C. W. Gilmore, Proc. V. S. Nat. Mus., vol. 36, 1909, p. 224, pi. 9, fig. 2, h. 



