100 PROF. W. K. PARKER ON THE STRUCTURE OF 



Hatteria; yet that of the latter (see Giinther, Phil. Trans. 18G7, pi. 1) is less aberrant 

 in many things than that of the Chameleon. The continuity of the stapes with the 

 hyoid arch is not a unique character ; that which is unique is the binding of the cheek 

 to the quadrate by a quadrato-jugal, a character which Hatteria has in common with 

 Chelonians, Crocodilians, and Birds. That type, however, has the vomers large and 

 distinct, and an epipterygoid the largest seen in any Eeptile. 



The most instructive skull for comparison w"ith that of the Common Chameleon 

 belongs to a Mexican Iguanian Lizard, viz. Lwrnanctiis longipes. Its size is about the 

 same ; and it is exquisitely ornate, aud possesses a very large interparietal crest. Yet in 

 nearly every thing this remarkable skull is normal, except in the development of the 

 crest. As in the Chameleon, the frontals are ankylosed together ; but the fontanelle, 

 although bounded by the frontal, lies on the edge of the parietal. That bone sends 

 outwards and backwards the normal " horns," that are articulated to the parotics, 

 supra temporals, and squamosals in the normal manner ; but it has also a large, flat, 

 vertical crest, formed by the gradual narrowing of the parietal bone from before back- 

 wards ; and this crest, keeping very nearly the line of the general gentle rise of the top 

 of the head, extends far backwards beyond the endocranium. But the supraoccipital 

 does not rise to meet it ; so that the height of the head behind is much less than in the 

 (Jhameleon. 



In the young of the Common Chameleon and in the adult Dwarf kind, we saw the 

 parietals as one bone: in the former a median forward outgrowth, belonging to the pair 

 of primary parietals, had yoked them together ; in the latter the three elements were 

 seen to be all lost in one large, crested, arched, tuberculate slab of bone. 



In Lwinanctus, undoubtedly, the primary bands that formed the beginning of the 

 parietal bones rapidly developed a common median outgrowth, that shot up into the 

 large lateral crest ; but I question if, at any time, there were three distinct bones. 



In comparing the skull of the Chaniteleon with that of Lacerta (see Phil. Trans. 1879, 

 y)late 42), I shall leave out of account the supernumerary bones that are seen over 

 the eyes and temples in that typical form, as well as in some others, such as Mocoa 

 (a " Scincoid "). 



The Common Chameleon differs from the typical Lizards — 



a. In the investing hones : 



\. Their highly ornate character. 



2. The frontals are fused together* and contain the fontanelle. 



3. The parietals are broken up into three bones, two parietals and an interparietal; 

 but the former are abortively developed, articulate with the end of the interparietal 

 crest, and are ankylosed with the squamosals. 



4. The prefrontals and postorhitals are articulated with each other over the orbit, thus 

 excluding the frontal from the outer ring. 



* Lizards are very variable as to this character. 



