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



The columella (figs. 4 & 7, co, st) has nothing to distinguish it from a feebly developed 

 ichthyic epihyal or hyo-mandibular, except its fusion proximally with the fenestral oper- 

 culum of the auditory sac (stapes). 



Its direction is downwards ; and it is bent outwards ; but it lies in the proper position 

 of an ichthyic epihyal, a position soon attained in fishes, where the postoral arches 

 are arranged telescopically ; that is, the lesser hinder arches pass within the larger 

 fore arches. The more directly outward direction of the epihyal, with a forward curve 

 round the quadrate, first shows itself in the Anura, where the tympanum is well 

 developed ; here, in the Chameleon, the closing-up of this cavity is correlated with the 

 retention of an ichthyic position of this element. 



I shall compare the skull of the young and adult, and both with the typical Lacertian 

 skull, when I have described the next type — one not so non-typical as the common 

 kind. 



Skull of Cham^leo pumilus, Adult Male. 



Morphologically, the skull of this species comes in halfway between that of the 

 young and the adult in the last species ; indeed, it has supplied exactly the link 

 I wanted between those stages to enable me to interpret the strangely transformed 

 roof-bones in the Common Chameleon. 



The supercranial valley (Plate XIX. fig. 3) is not so definite in this dwarf species, 

 nor is the interparietal crest so high ; moreover that crest is composed of only one, 

 not three, pieces. 



All the exposed parts of the investing bones are covered with a growth of tubercles 

 both really and relatively much larger than in the Common Chameleon. They are large 

 clear beads, or " guttae," of bony substance ; and these run in rows along the ridges and 

 in lines parallel with the ridges, — a structure better to be understood by reference to 

 the skull itself, or the figures of it, than by any description. 



The modifications seen in this skull as compared with the last are tendencies towards, 

 (or survivals of) what is typical; thus this is an excellent connecting link between 

 the normal Lizards and the abnormal Chameleon. 



Investing Bones of the Skull of the Dwarf Chameleon. 



The frontals (Plate XIX. figs. 1 & 3 (/) are completely ankylosed together ; and the 

 fontanelle (/o) is some distance in front of the coronal suture. This double bone is 

 square (roughly), with a wedge-like prolongation in front ; thus its anterior margins are 

 oblique and notched ; its posterior margin is emarginate, the parietal wedging in behind. 

 As in the young of the last kind, the frontal has a considerable orUtal tract (figs. 1 & 3, 

 /), as the prefrontals and postorbitals {pfpt.o) are far apart. The orbital regions of 

 the frontal are raised considerably at their edge ; and this is strongly beaded. 



The " valley " has a pair of submesial rows of bosses, and an irregular crop along the 

 middle ; the sutures all round the bone are strongly but irregularly toothed. 



