94 PROF. W. K. PARKER ON THE STRUCTURE OF 
The Endocranium of the Young Chameleon. 
The most striking things in this structure are the large, tumid, membranocranium 
and the massiveness of the auditory capsules (Plate XV. figs. 1, 3,4,7,&8). In front, 
up to the optic passages (1), the chondrocranium is merely an imperfect wall of 
cartilage, confluent with the twin capsules of the nose. 
The occipital arch is well developed both above and below; on its sides it is cramped 
and narrowed by the ear-capsules ; the condyle (0c. ¢) is suboval transversely ; the bony 
centres (¢.0, 0.0) barely reach it as yet. The foramen magnum (f. m) is very large, and 
fairly at the end of the skull. The bones are well bordered by cartilage, all save a 
space in front of the basal plate (fig. 2), where the floor is membranous; that bone, the 
basioccipital (4.0) is a large, thin, U-shaped plate, the horns of which enclose all but 
the fore margin of the large suboval posterior basicranial fontanelle (p. 6. ¢.f). A wide 
tract of cartilage separates this threshhold piece from the side plates—the exoccipitals 
(e.0) behind, and the opisthotics (op) further forwards. 
The exoccipitals (fig. 4, e.0) are narrow above and dilated below. The 9th and 10th 
nerves (IX, X) pass between them and the opisthotics (op); and the 12th (xm) pierces the 
bone. 
There is a considerable tract of cartilage between the exoccipitals and the crown of 
the arch, the superoccipital (s.0) ; this is to a considerable extent filled in by an exten- 
sion, backwards, of the epiotic (ep), a shell of bone of the form of a quadrant (fig. 7, ep). 
The supraoccipital has already sent upwards a squarish crest, rugged above; this ends 
in a rounded tongue of cartilage (fig. 8), which lies directly beneath the tongue-shaped 
interparietal tract (fig. 4, 7.) ; afterwards, as I have shown, this will be a high thin crest 
underpropping the high thin crest of the interparietal (Plates XVI. & XVII.). 
The outer view (fig. 7) shows the great triradiate synchondrosis between the three 
periotic osseous tracts. These are very unequal in size: the prootic (pr.o) is the largest, 
and is twice the size of the opisthotic (op), which again is twice the size of the epi- 
otic. The ampulle of the anterior and horizontal canals, and part of their arches, are 
contained in the prootic. The ampulla of the posterior and the end of the horizontal 
canals lie in the opisthotic; and the meeting part of the anterior and posterior is in 
the epiotic (Plate XVI. a.s.¢, h.s.¢, p. 8.¢, pr.0, OP; €p)- 
Below the arch of the horizontal canal, af, the postero-inferor edge of the prootic, 
there is an oval membranous space, the fenestra ovalis, filled by the stapedial end of 
the columella (fig. 7, pr.o, f. 0, st); the postero-inferior margin of the fenestra ovalis 
is enclosed by cartilage, which will be ossified by the opisthotic, which constantly 
forms the hinder edge of this space. The basisphenoid (4.s) is separated from the 
antero-inferior corner of the prootic by a cartilaginous tract, and also, above, from 
the horns of the basioccipital (fig. 8, 0.s, 6.0, _pr.o). But below (fig. 2) the basi- 
sphenoid sends back sharp horns of bone, which fasten on the ends of the broad horns 
