84 PKOF. W. K. PAEKER ON THE STEUCTUBE OF 



is seen a little distance behind the foramen ovale (v) ; the 9th and 10th nerves (ix, x) 

 escape between the ojiisthotic and exoccipital, the chink between these ankylosed bones 

 being large on the inside ; the 12th nerve (Plate XVI. fig. 4, xii) pierces the exoccipital. 

 The basisphenoid is a large vringed bone ; below (Plate XVI. fig. 2, bs), it is seen to 

 be split behind, and to have its hind margin somewhat concave to receive the rounded 

 fore edge of the basioccipital (b.o). It narrows forwards, is hollow both above and below 

 (Plate XVIII. figs. 11 & 12); and in front the part below the pituitary cup (Plate 

 XVII. fig. 1,^JJ/, b.fi) is no thicker than the base of the orbital septum, the end of 

 which it ossifies. That cup, the " sella turcica" (^J^y), has a thick bottom ; and its hinder 

 margin is the oblique forwardly-tilted postclinoid wall (jJ.cl). On each side of this 

 hollow the bone grows out as a large oblique expanding wing — the basipterygoid process 

 {b.pg), the direction of which is forwards, outwards, and downwards (Plate XVI. figs. 2, 4, 

 Plate XVII. fig. 3, and Plate XVIII. figs. 11 & 12, b.pg). These wings have a facet on 

 tlieir enlarged free ends; and these articulate with the facets of the pterygoid, the basi- 

 pterygoid processes lying between and below the pterygoid bones. The alisphenoid 

 (Plate XVII. figs. 1, 3, 4, al.s) arises from the prepituitary part of the basisphenoid: 

 it is a thickish semiosseous band, filling up scarcely a quarter of the alisphenoidal 

 region ; the rest is membranous. It is free and pointed above, the point lookmg 

 forwards in the membranous space. We miss here the latticework of cartilage seen in 

 the smaller and more typical Lizards (see Phil. Trans. 1879, pi. 43), both in the ali- 

 sphenoidal and orbito-sphcnoidal region. The Chameleon's alisphenoid is ossified in 

 its lower half ; and at its root and in its upper falciform part it is calcified more or less, 

 as in other Lacertilia. 



A large rounded space of membrane intervenes between the orbito-alisphenoid (Plate 

 XVII. figs. 1-3, o.s, al.s). This is not bounded by cartilage, but the roof-bone comes 

 down to this part and rests on these cartilaginous wings. This is where the upper part 

 of the huge postorbital {pt.o) wedges in over the orbit, behind the orbital plate of 

 the frontal (Plate XVI. fig. 1) ; the latter plate rests on the orbito-sphenoid, and 

 the postorbital on the interparietal, near its junction with the frontal. In old spe- 

 cimens (Plate XVII. fig. 3, j).s, o.s) the presphenoid becomes osseous ; this tract leans 

 against the ossified part of the alisphenoid, and descends at a right angle to that 

 bar; the cartilage is continuous between them. In the angle the large round optic 

 fenestra (ii) is seen ; and in front of the presphenoid there is an oval fenestra twice 

 the size of the optic passage ; this is the interorbital space {i. o.f) ; it is a long notch 

 in the Lizard {op. cit. pi. 43. fig. 8, i.o.n). Endosteal tracts are to be traced, in old 

 specimens, under the optic passage and under and over the interorbital fenestra, up to 

 the point where the middle wall belongs to the ethmoid {p.e). From the basisphenoid 

 to the anteorbital cartilage the basal line is slightly arched or concave ; the upper line is 

 still more concave (Plate XVII. fig. 3). 



In the upper view of the endocranium (Plate XVII. fig. 4), the orbito-sphenoidal 



