40 BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



Measurements of lower jaw of Stegosaurus stenops, No. 49.J4. Type. 



mm. 



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 



,, A preserved as shown in 



-a figure 9. The better 

 preserved element is 

 a long, flattened, 

 slightly curved bar of 

 bone. Comparing it 

 with the thyiohyal of 

 Camptosaurus which 

 was found in situ, 1 the 

 p\ -^~r**z0z£^~ '"''■- -3Sp|p^» J ~~ ' V " Y" ~\ expanded end prob- 



ably represents the 



Fit}; 9. — Thyrohyals of Stegosaurus sp. Cat. no. -1935, U.S.N.M. 5 Nat. size. IOrwarcl extremity. 

 Kelation? shown as found in the matrix, o, a, Anterior ends; p, posterior Sixty-eight millime- 

 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 F. A. Lucas, in an unpublished manuscript, observes "that judging from their 

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

 The principal measurements are as follows: 



■mm. 



Greatest length 174 



Greatest width of anterior end ._ 18 



Greatest width of posterior end 7 



External Openings in the Skull. 



Supratemporal fossae (e.). — The irregularly rounded supraoccipital openings 

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

 In S. stenops these fossae are bounded 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 is formed by the parietals, posteriorly by pro- 

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

 opening, externally by branches of the post-orbital and squamosal. . 



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

 openings 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 



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



