DEVELOPMENT OF THE SKULL IN THE CROCODILIA. 273 
Part of a section, much like this, is figured in Pl. LX VIII. fig. 2; here the columella 
(co) dents the auditory capsule (aw), the epihyal is just missed, and the head and 
shoulders of the ceratohyal (¢.hy) are cut obliquely across. 
But another section from a higher plane (Pl. LX VIII. fig. 1) is the most instructive ; 
here the columella or pharyngo-hyal fits into a hole, the fenestra ovalis, which opens 
into the vestibule (vd); on the inside that cavity is growing into its cochlear diverti- 
culum (chi). Here the small curved epihyal (e.iy) is cut across, and also (outside 
and below it) the head and shoulders (obliquely) of the ceratohyal (¢.hy). The 
fore part of the investing mass (iv), the body of the quadrate (q), and the first cleft 
(cl) are seen, as cut across, in this figure. 
In a lower section (Pl. LX VIII. fig. 4) the quadrate cartilage is seen sending its long 
orbital process inwards and forwards; behind it the ceratohyal (¢.hy) is cut across. In 
another figure (fig. 6) the ceratohyal (¢.hy, a7) is seen as cut across at its junction with 
the angular part of the mandible. 
In a still lower section (Pl. LX VIII. fig. 7) Meckel’s cartilage (mk) is cut across, and 
behind it, at the middle of the floor of the face, we see the basihyo-branchial plate 
(d.h.br) with the rudimentary first ceratobranchials (c.br'); these are gently curved, 
rounded rods of cartilage. In the lowest of these sections (Pl. LX VIII. fig. 8) the 
larynx (/x) is cut along; and here the curved thyrohyal or first ceratobranchial is cut 
in its curve so as to look like two pieces. 
The very ichthyic condition of these arches seen in this stage will be found to be 
greatly transformed in the stages that follow. 
The next stage will illustrate the further growth of the chondrocranium and visceral 
arches, and the first definite appearance of the investing bones. 
3rd Stage. Embryos of Crocodilus palustris, from 13 inch to 2 inches. 
a. Chondrocranium. 
This stage (Pl. LXII. figs. 5-9, Pl. LXIV. figs. 5-11, and Pl. LXVIII. figs. 10, 11) 
follows very closely upon the last, but belongs to another species and genus. 
I shall give all the details of the chondrocranium in the next stage, but in this 
the main things will be noticed; the cartilaginous framework is already perfectly 
formed. 
The notochord (Pl. LXIV. figs. 5-8, ne) is now closely embraced by the parachordal 
tracts, behind, and the cartilage has formed a semilune, below, half embracing it; this 
is the transversely oval occipital condyle (o¢.c). Then for three fifths of its extent 
the notochord is naked below, but it gains a superior position in front, the basal 
(parachordal) tracts having coalesced again beneath it. It escapes once more at the end, 
where it projects, inwards and upwards, into the neat circular pituitary space (py). The 
basal cartilage is dilated behind and in front of the auditory capsule, but is greatly 
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