148 REPORT — 1841. 



of the muzzle and its compressed form, equally remove it from the Croeodili- 

 ans. No Clieloniau has the tympanic pedicle so long, so narrow, or so freely 

 suspended to the posterior and lateral angles of the cranium. 



The general aspect of the skull differs, however, from that of existing Lacer- 

 tians, and resembles that of a bird or turtle, which resemblance is increased 

 by the apparent absence of teeth. The intermaxillary bones, moreover, are 

 double, as in Crocodiles and Chelonians, but, with this exception, all the essen- 

 tial characters of the structure of the skull are those of the Lizard. 



Of the proper walls of the cerebral cavity, the portion formed by the parietal 

 and frontal bones is exposed ; the parietal is traversed longitudinally by a thin, 

 but high, median crest; the part of the bone forming the sides of the small 

 cerebral cavity are convex, and the breadth of the bone diminishes towards 

 the occiput ; here it divides into two branches, which pass outwards more 

 transversely than in existing lizards. There is no perforation either in the 

 parietal bone or in the coronal suture. At the anterior part of the parietal 

 crest two lines diverge from each other at a right angle to the upper part of 

 the oi'bit, and separate the post-frontals. A nearly transverse suture divides 

 the fore-part of the parietal from the post-frontals. The median frontal bone 

 is single, like tiiat of the New World Monitors ( Thorictes, Tejus, <Src.) and the 

 Iguanse, and not divided, as in the Varanians. It expands slightly as it ad- 

 vances towards the fore-part of the orbits : the oblique lines dividing the 

 median frontals from the post-frontals, and the supraorbital ridges are raised, 

 so that the interspace is slightly concave, and the surface is also broken by 

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

 transverse suture. The posterior frontal completes the upper and outer part 

 of the orbit by a thin, well-defined, curved plate ; an irregular obtuse ridge 

 descends in a nearly vertical direction behind this plate, and then the posterior 

 frontal contracts and is extended backwards in the form of along compressed 

 process, gradually terminating in a point, which overlaps the zygomatic bone. 

 This bone forms the medium of union between the long posterior frontal and 

 the mastoid. 



The tympanic bone presents a slight sigmoid flexure, and is expanded trans- 

 versely at its distal extremity ; its posterior surface is exposed, which is con- 

 vex and rounded, and continued externally in the form of a thin plate, which 

 is concave behind. 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 Avhich the concave articulation of the lower jaw plays. The tym- 

 panic 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 bending out- 

 wards like the corresponding rim formed by the frontal bone. The anterior 

 or horizontal branch of the malar gradually tapers to a point which is Avedged 

 in between the lachrymal and maxillary bones. The posterior branch ascends 

 at nearly a right angle, and is apjilied 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. The lachrymal bone presents the same relative 

 position and size as in the Thorictes, Lacerta, and most lizards ; a tubercle 

 rises from about the middle of its external surface. The superior maxillary 

 is a broad vertical triangular plate of bone, with a smooth external surface ; 



