DEVELOPMENT OF THE SKULL IN THE CROCODILIA. 297 
nuclei of cartilage. But the columella itself is a continuous half-bony rod, and has 
lost its early segmental tract; it has also become fused, proximally, as one bony tract 
with the stapedial centre (Pl. LXIX. fig. 4, st, m.st). The bony shaft ends where the 
foliaceous forks begin; that lobe which is more directly a continuation of the primary 
( pharyngo-hyal) vod is the extrastapedial (e.st); it is falcate, with a free retral hook 
and a terminal crescentic dilatation. The suprastapedial stalk (s.s¢’) passes inwards, 
upwards, and backwards, and is a broad flap with a pedate free end, the “toe” of which 
is above. Behind, and a little below it, and quite detached backwards from it, is the 
pyriform suprastapedial segment (s.s¢), one of the upper links of the proper hyoid chain. 
To its broad lower end the epihyal, once more free, is attached by ligamentous 
fibres; it is a thickish nodule, with its lower end split; it is attached by its inner face 
to the sheath of the facial nerve (vir), the hinder fork of which emerges beneath it and 
the next nucleus; through the Crocodilian representative of the “ stylomastoid foramen” 
the great branch (vi) can be seen crossing the medio-stapedial, and running downwards. 
In front of the main nerve, but still behind the cleft, we see the remains of the 
main hyoid bar or ceratohyal (¢.hy); it is like an arrested rib, with a capitular and 
a tubercular process. The two lower nuclei both rest upon the lower part of the 
quadrate, behind, where the great semicircular tympanic notch is finished below 
(Pl. LXIX. fig. 4, g, and Pl. LXX. fig. 7). Close behind the ceratohyal we see the 
unossified free edge of the projecting ‘ paroccipital” (see also Pl. LXX. fig. 3, ¢.0); 
this is the part which in the Bird is developed so as to form a sort of cranial tympanic 
“bulla,” but whose office is largely held in the Crocodile by the quadrate bone; here 
the main cavity lies forwards, in the Bird it lies backwards. 
The distal part of the hyoid arch is only a region of the common distal rudiment of 
the hyoid and the “ first branchial” arch. There isa median cartilaginous, and a pair of 
lateral ossified, tracts; the former is a wide scoop, round in front, notched at the sides, 
and circularly emarginate behind. The side rods are the first “‘ ceratobranchials” or 
**thyrohyals ” (Pl. LXX. fig. 10, ¢.b7’); these are sigmoid rods, with a hooked, soft, free 
end, turning inwards, The tendency to form a lobulate hypohyal was arrested, and the 
whole median plate is merely developed as a wide, concave “ basihyo-branchial ” (4.07). 
c. The Investing Bones. 
Since the 5th stage (Pl. LX VI.) the outer bones have grown so as to finish a skull 
which is a very perfect miniature of that of the adult Crocodilian (Pls. LXIX.-LXXI.). 
The only instance of ankylosis is that of the basitemporals (Pl. LXX. figs. 1, 3, 5, 6.) 
with the basisphenoid (0.s). 
The upper fontanelle (Pl. LXX. fig. 2) is now completely obliterated, and the parietals 
and squamosals (p, sg) almost cover the hind skull. In the palate also (Pl. LXX. fig. 1) 
the palatines (pa) have hidden the vomers, and the pterygoids (pg) have united along 
the middle, and even coalesced behind and over the posterior nares (7.1); between 
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