286 PEOF. W. K. PAEKER ON THE STEUCTUEE AND 



mediostapedial rod (m.st), Trhose 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.st), 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 (i.st) disk, where it is confluent (with a trace of the junction left) 

 with the arched band below, the epihyal (e.%). This in turn is confluent with the 

 ceratohyal {c.hj), 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 

 (PI. 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 {st), 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.st) is figured within, and the extrastapedial {e.st) 

 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 di 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.st) is now 

 clearly distinct again from the suprastapedial stem {s.st') ; 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 

 (PI. LXV. fig. 9) shows a dilated basihyo-branchial plate {h.br), which is broad in front. 



