360 PROFESSOR OWEN, ON THE RHYNCHOSAURUS. 



irregular elevations and depressions. The post-frontal is divided by a 

 nearly transverse suture. This bone completes the upper and outer part 

 of the orbit by a thin well-defined curved plate; an irregular blunt 

 ridge descends in a nearly vertical direction behind this plate, and 

 then the posterior frontal is continued backwards in the form of a long 

 compressed plate gradually terminating in a point, which overlaps the 

 zygomatic bone. This forms the medium of union between the long 

 posterior frontal and the parietal fork. The posterior frontal is divided 

 by a suture, as in the Iguana?; the anterior division forms a projecting 

 curved plate at the upper and outer part of the circumference of the 

 orbit, and prolongs forward the rim of that cavity beyond the plane of 

 the head. 



The tympanic bone is bent like the Italic f, and is slightly expanded 

 transversely at its distal extremity : its posterior surface is exposed in 

 the present fossil, showing it to be convex and rounded, and continued 

 externally in the form of a thin plate, which is concave posteriorly. 

 The thick convex stem divides near the lower end into two ridges, 

 which diverge, like the condyles of a humerus, and intercept the trochlea 

 on which the concave articulation of the lower jaw plays. The tympanic 

 trochlea is convex from behind forwards, concave from side to side. 



The orbit is large, nearly circular in form, and its bony frame is 

 complete; this is formed above by the median, anterior and posterior 

 frontals, before by the anterior frontal and lachrymal, below by the 

 malar, and behind by the malar and posterior frontal. 



The malar bone, as in most lizards, is long, slender, and bent upon 

 itself, but its external surface is unusually concave, the orbital plate 

 projecting outwards, like the corresponding rim formed by the frontal 

 bone. The anterior or horizontal branch of the malar gradually tapers to 

 a point, which is wedged in between the lachrymal and superior max- 

 illary ; the posterior branch ascends at nearly a right angle and is 

 applied obliquely to the posterior part of the descending process of 

 the posterior frontal : at the angle between the two portions of the 

 malar a process is continued backwards for about half an inch, but its 

 extremity is broken off. 



