THE SKULL IN THE CHAMELEONS. 87 
is cut through in the epiotic, and the arch of the horizontal canal (h. s.c) is cut through 
in the prootic (pr.o). That bone extends outwards, and flanks the “paroccipital,” 
or wing of the combined opisthotic and exoccipital (fig. 4, pr. 0, op). ‘The vestibule (vd) 
is laid open in this section, and the passage into it, viz. the fenestra ovalis (f. 0), close in 
front of the columella. Below this opening a wedge of bone is seen: this is the antero- 
inferior part of the opisthotic (op); see also fig. 1. Here the section of the cranial 
cavity is hourglass-shaped, the auditory capsule bulging inwards; the stem of the tri- 
radiate synchondrosis, between the three periotic elements, is here cut through down- 
wards, and the cartilage of the anterior fork, between the epivtic and prootic, is cut 
across. ‘The 4-edged wedge of bone belonging to the opisthotic (op) rests obliquely 
upon the edge of the fore part of the basioccipital (4.0), which is at its broadest 
here: it is gently concave above, and much more scooped below (see also Plate XVI. 
fig. 4, 6.0). In the next section (Plate XVII. fig. 6), the epiotic and supraoccipital 
(ep, 8.0) are continuous, and are of great extent (see also figs. 1, 3, 4); the spinous 
process is thinner, and passes gradually into the roof (s.0), which also passes into the 
epiotic (ep). This region contains the neck of the anterior canal (a. s.c) where it is 
passing into that of the posterior canal. The horizontal canal (A. s.c) is seen in section 
in the prootic (pr.o); and the vestibule (vd) is shown opening out at the fenestra ovalis 
(f.0). Here the stapedial end of the columella (st) is seen filling up the opening, and 
the rest of the columella (m.s¢, e.st) is shown attached to the inside of the quadrate, 
which is cut through obliquely, showing the pedicle (pd) and the shoulder of this pier 
(q). The investing bones over this part are not figured. Here a thin wedge of the 
opisthotic (op) is cut through ; this is the part which in higher Lacertilia divides the 
fenestra ovalis from the fenestra rotunda. At this part the opisthotic is distinct from 
the exoccipital; this latter bone (¢.0) is here shown as helping to form the passage for 
the 9th and 10th nerves (1x, x). The basioccipital (0.0) is here at its narrowest part, 
close in front of the occipital condyle. 
The next section (Plate XVII. fig. 7) is through the root of the condyle, the 
thickest part of the parotic process (op), and the hind part of the quadrate (7), behind 
the columella. The posterior canal (p.s.c) is here cut through; and here the ridged 
roof-piece (8.0, ep) is very solid. ‘Lhe vestibule (vd) is still seen behind the fenestra 
ovalis: this is the part of the sac which corresponds to the more distinct rudiment of 
the cochlea, seen in the higher kinds of Reptilia (including most Lizards). The vesti- 
bular sac here intervenes between the exoccipital (¢.0) and the opisthotic (op), which has 
here its most solid and outstanding part, forming most of the “parotic process.” ‘The 
basioccipital (0.0) has here widened again somewhat before its end in the substance of 
the condyle. This section is behind the prootic and the two front canals; the quadrate 
(q) is cut down from the otic process (of. p) to its lower condyle (g.c¢). The cartilage 
on the inner face of the auditory sac is the hinder fork of the triradiate tract (see 
fie. 1). 
g. 1) as 
