OSTEOLOGY OF THE ABMOKED DINOSAUKIA. 



27 



Known elements of the Stegosaurian skull. — 



Alisphenoid al. sp 



Angular an 



Articulai- ar 



Basispheiioid Js 



Basioccipital 60 



Deutary ^ 



Exoccipital ex.o 



Frontal y 



Jugal j 



Lachrymal i 



Maxillary m 



Na-sal jj 



Orbitosphenoid or.sp 



Palatine pi 



Prespheiioid p,sp 



Paraoccipital (opisthotic) p.oc 



Parietal n 



Postorbital pg 



Postfroiital pQ J- 



Posts Lipraorbital. no. so 



Pi'efrontal pf 



Preiaaxillary p^ 



Prearticular „ ^^ 



Predeiitary pj 



Presupraorbital p sq 



Prootic pj.Q 



Pterygoid - pi 



Quadrate « 



Quadratojugal qj 



Splenial g 



Squamosal g„ 



Surangular jq 



Supraoccipital gg 



Vomer . . „ 



<^— i:^ 



FiQ. 3.— Skull OF Stegosaurusstenops Marsh. Lateral view. Type. Cat. no. 49.M, U S N M 



LE.SS THAN 1 NAT. SI2K. a. ANTERIOR NARES; an, ANGULAR; ar, ARTICULAR; b, ORBIT; C, tNTBA 

 TEMPORAL F0S.<!A; d. DENT.VRY; j, JUGAI,; l, LACHRYMAL; m, M.LmLARY; n.NA.SAL; OC, OCCTPrTAl 



condyle; p.ar, prearticular; pri, predentary; pf, prefrontal; pm, premaxillaey- pn 



POSTORBITAL; p. OC, PARAOCCIPITAL; po.so, POSTSUPRAORBITAL; p.SO, PRESUPRAORBITAL; 7, QUAD- 

 RATE; qj, quadratojugal; s, splenial; sti, surangular; ,??, squamosal. 



Description.—A study of this material shows that Marsh's figures of the skuU 

 of Stegosaurus stenops, which have appeared in numerous Americian and European 

 pubhcations, are incorrect in many of their details. The inaccuracies are in great 

 part due either to the complete coalescence or to the obscure condition of many of 

 the sutures, and also in some instances to a wrong interpretation of cracks in the 

 skull (No. 4934) as representing sutural articulations. These errors have been cor- 

 rected in the drawings, and a more detailed mention of them will follow in the 

 discussion of the separate skull elements. 



Viewed from the side (pi. 5 and fig. 3) the skuU of Stegosaurus is long and slender, 

 the facial portion being especiaUy produced. With the jaw in position the outline of 

 the skuU IS wedge shaped, the apex being directed forward. The nai-es are long, 

 and, as m Gamptosaurus, are situated well in front. The orbit is large, measuring 

 about one-fifth of the total length of the skull, and placed well back. The infra- 

 temporal fossae ai-e somewhat smaller. Marsh has pointed out that "all of these 



