STENEOSAUEUS. 87 



of the upper border of a vascular groove which crosses the back wall of the temporal 

 fossa (see below). 



The postfrontal (po.f.) unites by an oblique suture with the outer (postorbital) 

 process of the frontal, and forms the lower part of the bar of bone separating the orbit 

 from the supratemporal fossa : at its ventral end it unites with the jugal, and behind 

 this it is prolonged backwards as a broad band of bone to the zygomatic process 

 of the squamosal (sq.), uniting with it in an oblique suture ; this posterior bar, 

 which constitutes the anterior two-thirds of the upper temporal arcade, is somewhat 

 thickened along its upper border, but is thin and sharp below, the lower part of the 

 outer face being marked by a longitudinal groove. 



The squamosal (sq.) is an L-shaped bone. One arm of the L extends up to the 

 parietal, with which it forms the posterior boundary of the supratemporal fossa. Its 

 posterior face is almost completely concealed by the overlap of the exoccipital. 

 Its anterior face is marked by a deep but short transverse groove, the inner end of 

 which passes by a foramen into the skull, the outer probably passing out at the back 

 of the skull by an opening between the squamosal and upper edge of the quadrate. 

 Mr. D. M. S. Watson drew my attention to this canal in a skull of MystHosaurus from 

 the "Whitby Lias; it seems to occur commonly in the whole group and probablv 

 transmitted a blood-vessel. The zygomatic branch makes nearly a right angle with 

 that running up to the parietals, but the actual angle is truncated by an oblique 

 surface, concave above and convex below, and defined in front by a strong ridge, 

 roughened and sloping downwards and backwards. The surface probably served fur 

 the attachment of muscle, while the anterior ridge perhaps had some relation to the 

 tympanic membrane, or perhaps to the muscles connected with a flap closing the outer 

 ear. The zygomatic bar itself is comparatively short and narrow ; it unites in front 

 with the postfrontal. Ventrally it joins the quadrate, which sends a process forwards 

 along its ventral edge probably to the postfrontal, and another backwards, forming the 

 upper edge of the narrow cleft-like opening of the tympanic recess, the lower edge of 

 which is formed by the body of the quadrate. The backward process of the quadrate 

 along the squamosal extends nearly to the prominent ridge on the latter bone referred 

 to above. 



The quadrate (q.), of which the prolongation upwards to the squamosal has just 

 been described, is a very large and strongly built bone fixed immovably among the 

 surrounding bony elements ; it is directed downwards, outwards, and backwards and 

 terminates in the articular surface for the mandible. This surface consists of an inner 

 and an outer convex portion separated by a shallow groove which passes across it 

 obliquely from above downwards and inwards. Immediately above the outer angle of 

 the articulation the outer border of the bone unites in suture with the expanded 

 posterior end of the quadrato-jugal, and above this runs up to the squamosal, with 

 which it unites in the manner described above. The upper surface of the ascending 



