DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 179 



(Plates 34 and 24), but I liave looked fov it in vain in most of the skulls of the 

 Anura. 



The girdle-bone reaches in front to the full extent of the ethmoidal region, but at 

 the sides does not ossify the " alse." From the axils to witliin a short distance of the 

 hind margin there is a large oblong fossa : this is due to a very remarkable structure, 

 viz. : the filling in by periosteal bone of a pair of large oblong fenestrse in the side- 

 walls of the skull, in front of, and similar to, the optic fenestrte (II.). In Rcvppia 

 hicolor (" Polypedatidfe ") (see Plate 19, figs. G, 7) and in Camariolius tasmaniensis 

 (" Cystignathidse ") those two spaces are continuous (Plate 19, figs. 1, 2) ; it is possible 

 that the orbito-nasal nerve may have passed into the skull in the front part of this 

 space, which is very anomalous. The septum nasi (s.«.) is thick and well marked, and 

 ends in a distinct, but short, prenasal (fig. G) ; the roof and floor (on each side of s.n., 

 above and below) are well developed, and the new cornua, or pro-rhinals {p.rh.), are 

 miniatures of the primary cornua trabeculae. 



The sub-tid3ular nostrils [e.n.) have a definite raised rim ; they are not very wide apart, 

 and have the usual appendages {u.l\u.P.) which are well developed. The inner nostrils 

 {i.n.) are much wider apart; the ethmoidal alse are broad up to their outer edge, behind ; 

 there the cartilage, now ethmo-palatine {e.pa.), is much narrower and then expands 

 outside into the jore-palatine plate {pr.pa.). The bone (/'«.) only partly hides the 

 cartilage; it is almost straight and dilates outside; the pterygoid {p>9-) ^'^^^ ^o*' 

 reach it by a considerable distance ; that bone and the correlated cartilage is very 

 slender. The bone continues so, but the cartilage dilates considerably to form the 

 swelling pedicle {pd.) and the obhque bdobate trochlea of the quadrate {q-c); the 

 cartilage above the joint {q.) is considerably ossified from the quadrato-jugal {q.j.). 



In the right angle formed by the suspensorial forks the Eustachian opening {eu.) is 

 seen to be large and crescentic. The " annulus " {a.ty.) is of normal size, but is open 

 above. The stapes (figs. 10, 11, st.) is a thick oblique valve, hollow within and thickest 

 at its lower edge ; it has a crescentic emargination for the inter-stapedial [i.st.) and a 

 definite, oblong "umbo" outside. The inter-stapedial {i.st.) is a large saddle-shaped 

 segment, half the size of the stapes ; the medio-stapedial [m.st.) has the average pistol- 

 shape, and a nearly perfect joint divides its unossified end from the symplectic element. 

 This latter {e.st.) is a rod of cartilage, duckbill-shaped, with a thin flange ; this extra- 

 stapedial gives off from the end of the flange a ligulate supra-stapedial {^.st.), which is 

 confluent above. 



The mandible (fig. 8) is perfectly normal. 



The fixed stylo-hyal passes into the cerato-hyal region (fig. 9, c.hy.) without enlarging; 

 the cartilage has a sharp inturued horn before it grows back as the hypo-hyal (h.hy.). 

 The notch is very large and transversely oval ; the body of the basal plate (b.h.h?:) is 

 extremely short, and ends behind in a small free rounded lobe, in front of which there 

 is an endosteal basi -branchial {b.ln-\) ; outside this the thyro-hyals (t.hy.) are extremely 

 long and bound a space which is half a long ellipse ; theii- liinder third is unossified. 



2 A 2 



