32 
MR. W. K. PARKER OK THE STRUCTURE AND 
Then comes a short exoccipital bone (e.o.) right and left, and then a considerable tract 
of cartilage between these and the supraoccipital bones ( s.o .) above. The cartilage in 
which these latter centres lie is continuous with the broad, sinuous supra-auditory and 
orbitosphenoidal belt ( s.a.c ., o.s.). Seen from above, the huge auditory capsules, with 
their apiculated helical cochleae (chi.) are seen to be confluent with the proper chondro- 
cranium both in front of and behind the passage for the 9th and 10th nerves. A 
notch separates each cochlea from the upper mass of the capsule, and a well-formed 
archway is formed by the proximal coil of the cochlea over and in front of the com¬ 
pound meatus interims (VII., VIII.). 
The end view of the chondroeranium (fig. 2) shows what a large occiput these types 
possess. The supraoccipital centres (s.o.) are still distinct, and meet over the foramen 
magnum ( f.ni .), which is ovoidal in form, with the narrow end above ; they occupy 
less than half their own region, at present. The exoccipitals (e.o.) are largely hidden 
in this view by the ear-shaped condyles (oc.c.); in front of these, the cochlea (chi.) 
can be seen, below, and in the distance. The paroccipital elevations outside the 
condyles are but little developed ; the cartilage is nearly convex. A lozenge-shaped 
tract of the ear-capsule is seen above their convexities, right and left, and all the three 
canals (ct.s.c., h.s.c., p.s.c.) can be seen shining through it, so great is the obliquity of 
the capsule in its cranial setting ; the large inner (IX., X.) and the lesser outer (XII.) 
nerves are also seen (the dotted line is wrong). 
The tympanic region, from the outside, has been separately worked out and figured 
(fig. 3) on a larger scale. The annulus ( a.ty.) is fast becoming bony, especially in the 
end of the upper crus, where it is partly bifid, above, to form a rest for the processus 
gracilis of the malleus (ml.). That element is still a perfect mandible in itself; the 
stem (mk.) is drawn as cut across, in the figure. 
The depth of the sinuous selliform condyle for the incus (i.) explains why the 
malleus shows a hole at this part in the section (Plate 4, fig. 7). The styliform 
ectostosis is now expanding and embracing the under face of the head of this 
bar; below and inside this bony tract the tensor tympani muscle (t.tm.) can be 
seen arising by a narrow and short tendon, and then passing upwards and inwards, 
solid and fleshy. The posterior angular process behind the internal, or manubrium, 
is very indistinct; the latter is nearly parallel with the main bar. The sinuosities of 
the condyle of the well-formed but unossified incus (i.) correspond with those of the 
malleus ; the short crus (s.c.i) is thick, and fits into a neat cup in the auditory 
capsule, close over the ampulla of the horizontal canal (h.s.c.). The thick, long crus 
is almost parallel with the elbowed part of the malleus; it has a well-formed 
orbicular facet on its inturned end. The unossified stapes (st.) is also large and well 
formed; here it is figured looking outwards, inside the incus ; its ovoidal base has the 
narrow end looking upwards and forwards, according to the shape of the fenestra 
ovalis (fs.o.). The tendon of the stapedius muscle (st.m.) shows in its substance a 
considerable nucleus of cartilage, the interhyal (i.hy.) or infrastap3dial. The slice of 
