DETELOPIMENT 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) rod is the extrastapedial (e.si?) ; it is falcate, with a free retral hook 

 and a terminal crescentic dilatation. The suprastapedial stalk (s.5^) 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.st), 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 (vii), the hinder fork of which emerges beneath it and 

 the next nucleus ; through the Crocodilian representative of the " stylomastoid foramen " 

 the great branch (vii) 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 [c.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, q, 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, e.o); 

 this is the part which in the Bird is developed so as to form a sort of cranial tympanic 

 "bulla," but whose office is lai'gely 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 is a 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, cW) ; 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 " (h.br). 



c. The Investing Bones. 



Since the 5th stage (PL LXVI.) the outer bones have grown so as to finish a skull 

 which is a very perfect miniature of that of the adult Crocodilian (Pis. LXIX.-LXXL). 

 The only instance of ankylosis is that of the basitemporals (PL LXX. figs. 1, 3, 5, b.t) 

 with the basisphenoid [h.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 [i. n) ; between 



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