DEVELOPMENT OF THE SKULL IN THE CEOCODILLi. 275 



exactly the same position, and general anatomical relations, as the permanently non- 

 segmented and unossified counterpart in the " Urodeles." 



In the Turtle (Skull of Chelone, ' Challenger Reports,' vol. i. pt. 5, pi. 10. fig. 7) the 

 small epipterygoid is at first a flaj) of cartilage hanging down from the apex of the 

 orbital process of the quadrate, which afterwards becomes segmented and ossified ; it 

 corresponds with such a remnant q/ cartilage as is often seen on the pterygoid hone in 

 adult Urodeles. 



To any one familiar with the rich development of the visceral arches in Fishes, and 

 aware that the mandibular is merely a highly modified visceral or branchial arch, these 

 modifications will present no real diflSculty. Morphologically speaking, the quadrate 

 is an epibranchial, and the articulo-Meckelian rod a cerato-branchial element. Any 

 separate cartilages developed between the antorbital and postorbital regions of the 

 palate are merely to be looked upon as segments or dismemberments of the epibranchial 

 piece — the quadrate. Above the Fishes, I know of no other segment in this arch that 

 can with safety be called pharyngo-branchial, except the epipterygoid of the Lacertilia ; 

 I am doubtful even about that of the Chelonia, which is developed diflerently ; but the 

 " ethmo-palatine " and " post-palatine " rudiments so well seen in the Axolotl (" Skull 

 of Urodeles," Phil. Trans. 1877, pi. 24. figs. 1-3) are all (/ noiu consider) to be looked 

 upon as remnants of the huge " ptery go-quadrate " of the Shark. 



The lower or articular part of the quadrate of the Crocodile is now closely embraced 

 behind by the cerato-hyal (PI. LXVIII. fig. 10, q.c, ar, c.hy), and the articular head of 

 the mandible sends backwards a large, notched, angular process. 



The hyoid arch (PI. LXVIII. figs. 10, 11) is now perfect; the uppermost piece (or 

 pharyngo-branchial element) has now become a long " columella ;" it is only partially 

 distinct from the cartilaginous operculum (base of " stapes ") of the auditory capsule ; in 

 this the Saui'opsida diff'er from the Amphibia, which have the stapes and medio-stapedial 

 separate. Yet, as I have shown in my former papers on the Reptilian skull, the ring of 

 thin cartilage embracing the dorsal end of the uppermost hyoid segment is partially a 

 separate tract of cartilage, whose cells are much flatter and less characteristic of that 

 tissue. I shall soon show that a separate bony centre is formed in the stapedial end 

 of the columella (PI. LXIX. figs. 2, 3); these parts are special developments of the 

 hyoid. 



As in the branchial arches, proper, of the Sturgeon, this pharyngo-hyal piece is 

 subdivided ; the proximal segment forms the base and stem of the columella [st, m.st), 

 and a process to which the suprastapedial (s.sf) is attached ; the distal piece is the 

 extrastapedial part. 



The columella is comparable both to a pruning-hook and a scythe ; it has two side 

 handles, and ends in a broad blade with a thickened convex back. The back is turned 

 outwards and upwards (fig. 10, e.st), and overlies the concave bevelled postero-superior 

 edge of the quadrate cartilage ; and the sharp concave edge looks upwards and inwards. 



