286 PROF. W. K. PARKER ON THE STRUCTURE AND 
mediostapedial rod (m.st), whose dilated base is nearly of the same length as the 
outstanding bony bar. The two foliaceous outgrowths of this remarkable ‘“‘ pharyngo- 
hyal” grow, the one inside, upwards, backwards, and inwards; and the other outside, 
forwards, upwards, and outwards, very obliquely. 
The broadening curved blade of the suprastapedial stalk (s.st') has its outer face 
ribbed, and its broad, backwardly turned top confluent with the auriform suprastapedial 
segment (s.s¢), whose upper part is bilobate, its lower part rounded, and its proximal 
edge thick and solid. Together these parts describe an accurate semicircle by their 
lower edge. 
The extrastapedial (e.st) is seen somewhat edgewise (see also fig. 2); both its inner 
and outer edges are ribbed, and the latter dilates into an elegant crescentic hook, 
above. Below, this process becomes twisted, narrower first, and then dilated into an 
oval interstapedial (7.s¢) disk, where it is confluent (with a trace of the junction left) 
with the arched band below, the epihyal (e.hy). This in turn is confluent with the 
ceratohyal (¢.hy), but shows the joint. That joint is behind the broadened head of the 
lower bar, which is gradually attenuated, until it becomes a ligament, attached to the 
original point of confluence with the mandible. 
This is not all; for the ceratohyal itself is half segmented in the middle; the lower 
part it will soon degenerate into a fibrous tract. 
A week later on (August 4th) brings us towards the later changes of these parts 
(Pl. LXIX. figs. 2, 3), here the parts are also seen from the outside, but drawn out 
so as to display them better. 
The oval stapedial plate, with its inner, central, growing bone (s#), is very large, and 
has a rounded edge for the fenestra ovalis; the shaft, as in the last, is seen to arise 
much above the middle. 
This almost straight, slowly attenuating rod, ends below the outgrowing distal, leafy 
growths; the suprastapedial (s.s¢) is figured within, and the extrastapedial (e.s¢) 
without. 
All the old seams, or lines of segmentation, have opened again, with the exception of 
that across the columella (see Pl. LXVIII. figs. 10-14); this is like the dehiscence of 
“ carpellary leaves” that begin in the bud as distinct members of the innermost whorl 
of a flower, then unite, and reopen, afterwards, to shed the seeds. 
The main distal plate, extrastapedial (e.st), is like a bill-hook, but is dilated in an 
arcuate manner above and below; there is an articulation to the curved segment 
(epihyal, e.hy) which articulates below with the ceratohyal on one side of its dilated 
upper part; the lower part is lessening fast. The suprastapedial segment (s.s¢) is now 
clearly distinct again from the suprastapedial stem (s.s¢'); it has developed a pedate 
process inwards from the point of junction above. 
The distal part of the second and third visceral arches of the embryo Alligator 
(Pl. LXV. fig. 9) shows a dilated basihyo-branchial plate (h.67), which is broad in front, 
