OSTEOLOGY OF THE AKMOKED DLNOSAURIA. 



35 



On account of the complete coalesence of the quadrate with the quadratojugal 



in the skull of S. stenops, No. 4934, Professor Marsh was not ahlo to detect its 



presence as a separate element, and in the original draw- 

 ings of the skull it was indicated as a forwardly directed 



process of the quadrate. 



Quadrate (q.). — The quadrate, a large, stout bone, is 



transversely compressed throughout its upper half into a 



quadrangular plate. Toward the distal end, however, it 



thickens in all dimensions. In the skull of S. stenops (No. 



4934) both quadrates have been retained in their natural 



relations and are but little distorted. (See fig. 2, pi. 9.) 

 The right quadrate of this specimen has a length of 



129 mm.; the left element, which has been more subjected 



to vertical pressure, is somewhat shorter. The antero- 

 posterior diameter of the quadrate (right), just below the 



squamosal end, is 39 mm. ; and just above the mandibular 



end is 24 mm. The transverse width of the latter end 



is 33 mm. 



Viewed from the side the quadrate is capped by the 



squamosal, the truncated top, fitting within a recess on the 



under side of that bone. On the posterior internal side 



(shown by the quadrate of No. 6645, see fig. 6), below 



the squamosal end, a flattened, slightly striated surface 



rests against the outer anterior face of the paraoccipital 



process. Near the middle of the quadrate a vertically 



flattened process is given off, which extends anterior to 



the longer axis of the bone. This internal process turns slightly inward and unites 

 by a lapping suture with the posteriorly directed process from 

 the pterygoid (see pt., pi. 8). 



The articular end for the jaw is rectangular in outline. 

 Viewed from behind the articular end is cut off obliquely 

 to the longer axis of the bone (fig. 2, pi. 9). This view also 

 shows on the posterior surface the pronounced longitudinal 

 depression in the shaft of this bone. Text figure 6 is based 

 upon the detached quadrate of No. 6645. In old individuals 

 the quadrate appears to become fixed, as shown by specimens 

 Nos. 4934 and 4936. 



Squamosal (sq ). — The squamosal, as shown in pi. 5, 

 unites by an anterior branch with the postfrontal and by 

 a shorter, heavier, inner process with the parietal. It thus 

 helps to bound the supratemporal fossa posteriorly. In- 

 ternally the lower posterior edge rests upon the upper 

 border of the paraoccipital process, but more externally it 

 passes below and in front of that bone. (See figs. 4 and 5.) 



It caps the upper end of the quadrate, which is fitted into a recess on its under 



side. A ventral view of this bone is shown in figure 7. 



Fig. 6. — Left quadrate and quad- 

 ratojugal of Stegosaurus 

 stenops? Marsh. Cat. no. 6545, 

 U.S.N.M. J Nat. size. Side 

 view, a, Articular end foe 

 lower mandible; 6, end which 

 meets the squamosal; q, quad- 

 rate; qj, quadratojugal. 



Fig. 7. — Ventral view of left 

 squamosal of Stegosaurus 

 stenops? Maesh. Cat. no. 

 6645, U.S.N.M. h Nat. size. 

 o, Sueface foe articulation 

 with the quadrate; b, 



SUTURAL SURFACE THAT 

 UNITES WITH PARIETAL; C, 

 PROCESS WHICH EXTENDS 

 FORWARD TO MEET THE POST- 

 FRONTAL. 



