THE SKULL IN THE CHAMELEONS. 95 



of the U-shaped basioccipital. The hinder margin of the basisphenoid is lunate, 

 not semielliptical, like the fore margin of the basioccipital ; its axial length is only half 

 as great as that of the hinder bone. The basisphenoid would be a triangular wedge 

 (for it ends in an almost pointed process in front) ; but it gives off at the middle on eacli 

 side a wing of bone, dilated and cartilaginous externally. These wings are the basi- 

 pterygoid processes (b.pg), whose direction is downwards, outwards, and forwards. 



The openings for the trigeminal nerves (v) are surrounded by membrane everywhere 

 except a small tract below and behind ; for here, in the alisphenoidal region, the mem- 

 branocranium (al.s.f) extends over the highest part of the head, and down on each side 

 to the base (fig. 7). The alisphenoid (al.s) is a feeble sigmoid bar in front of this space ; 

 it is continuous with the basal cartilage, between the optic passage and the foramen ovale 

 (ii, v), and with the orbito-sphenoid (o.s) above the common optic passage. The lower 

 half is ossifying, and is arched backwards ; the upper half, which only reaches up to the 

 most tumid part of the membranocranium, is soft, and bends forwards. Between this 

 feeble rudiment of the " ala magna " and the orbito-sphenoidal lamina there is a deepish 

 triangular notch. 



The chondrocranium in front of the ali- and basisphenoid is quite unossified ; in front 

 of the great common optic passage (ii) there is an oblique presphenoidal band (^j.s) run- 

 ning downwards and forwards to the trabecular base. In front of this there is a large 

 oblong interorbital fenestra (i.o.f), not notch, as in Lacerta. 



The thick trabecular base below and the thin lamina above this fenestra are about 

 equal in depth. From the upper part there proceed a pair of narrow orbito-sphenoidal 

 wings (o.s) ; these soon become almost obsolete, and then widen in the ethmoidal 

 region, where they are pierced by the olfactory nerves (i) and lie over the orbito-nasais 

 (yi). The perpendicular ethmoid becomes a low middle wall, passing into the septum 

 nasi (figs. 7 & 8), which divides the flat, but tumid, 4-celled nasal labyrinth, with its 

 annular outworks [al.sp, al.n). From the postero-inferior face of the capsule there is a 

 small semioval cartilage projecting ; this is the ethmo-palatine {e.pa) 



The Pastoral Arches in the Young Chameleon. 



The whole articular head (otic process) and the pedicle and the base of the quadrate is 

 still soft (fig 1, ot.i),])d, q. c); and part of the free mandible is unossified nearly to the con- 

 dyle, not being covered, as yet, by the articulare (fig. 6, 7)i/i, ar). The long glosso- or 

 basihyal rod, with its small terminal segment (tig. 8, c.hr,h.hy, h.hy^), is unossified; also 

 the ceratohyals {c.hij) and hypohyals {h.hy). The thyrohyals, or 1st cerato-branchials 

 {c.hr), are well ossified already. 



The long azygous rod is not quite so long, relatively, as in the adult ; it only reaches, 

 if measured by the basis cranii, from the occipital condyle to the middle of the septum 

 nasi. Q 2 



