OSTEOLOGY OF THE SKULL OF THE DIMETRODON ra 
Anterior to the quadrato-jugal is another element in the position 
usually assigned to the quadrato-jugal; 7. ¢., it articulates with the 
jugal anteriorly and passes back to articulate with the quadrate 
region. It is separated from the quadrato-jugal posteriorly (which 
is identified beyond doubt by the presence of the quadrate foramen) 
by a distinct suture, and occupies the exact position of the anterior por- 
tion of the squamosal of the living Sphenodon. It is separated from 
Fic. 2.—Restoration of the left side of the skull of D. gigas. bo, basi-occipital; bs, 
basi-sphenoid; /, frontal; 7, jugal; /, lachrymal; mx, maxillary; 7, nasal; pmx, pre- 
maxillary; pv, prevomer; pt’, ascending plate of pterygoid; pt, pterygoid; /, prefrontal; 
ptf, postfrontal; pto, postorbital; pa, parasphenoid; psq, prosquamosal; ps, ethmoid; 
po, paroccipital (opisthotic); g, quadrate; sq, squamosal; st, stapes. 
the squamosal above by the meeting of the quadrato-jugal and parie- 
tal; but if these were to separate, and the squamosal and this element 
came in contact or fuse, we should have the exact condition of the 
primitive Rhyncocephalia (Saphaeosaurus), or Sphenodon. For this 
reason I have determined the bone as the prosquamosal. ‘This bone 
articulates posteriorly with the postorbital, quadrato-jugal, and the 
lower extermity of the parietal. 
The inferior temporal vacuity is formed by the jugal, prosqua- 
mosal and postorbital. It is nearly as large as the orbit. ‘The supe- 
rior temporal vacuity is formed by the postorbital, prosquamosal, 
quadrato-jugal, and parietal. It is very small, amounting to a small 
