178 MR. W. K. PARKER OX THE STRUCTURE AND 



6. The ethmoidal roof gives off large superorbital outgrowths. 



7. The palatine bones are unusually developed, taking on the dilated form of the 

 corresponding cartilages. 



8. The ptei-ygoid bone, like the cartilage on to which it is grafted, is slender, but it 

 articulates, by suture, with the bony skull, and fixes the pedicle. 



9. There are neitlier inter- nor supra-stapedial. 



10. The basal plate is largely membranous in front, and all the "lobes" are small. 



11. There are no septo-raaxillaries. 



12. The fronto-parietals o,re narrow, arrested bands. 



49. Hyla 7'ubra. — Adult male ; 1 inch 11 lines long. South America. 



This is a lightly built, but strong, skull (Plate 33, figs. G, 7) ; its greatest breadth is 

 to ite length as 1 1 to 1 0, and its general outline is seven-twelfths of a very neat oval ; 

 the incurving of the quadrato-jugai {q.j.) gives a sixth of the (supposed) other half of 

 the figure. The condyles of the quadrate [q-c.) reach as far back as the upper edge of 

 the foramen magnum {f.rn.). 



It is a flat, wide skull, the "parotics'' beyond the horizontal canal (h.s.c.) doubhng 

 the width of the capsule, right and left. The axial extent of the hind skull is only 

 two-thii'ds as great as that of the other two regions, which are equal. 



Measured across the ethmo-palatine wings withm the raaxillaries (e.pa., mx.), in 

 front, and aci'oss the tegmen tympani of each side within the squamosals (sq.), behind, 

 the chondrocranium has the same breadth. A considerable synchondrosis exists above 

 and below, at the mid-line {f.m.); between the small, oval, posterior condyles (occ.) 

 the basal outline is convex, and is equal to both the facets in breadth ; the arch, above, 

 comes short of the basal plate only moderately ; the obUquity of the foramen magnum 

 is not great. 



The extent of the outstanding ear-capsules is twdce as great against the skull as at 

 the tegmina (inside sq.) ; each tegmen is ossified for one-thu'd of its extent, and the 

 bony tracts are not divided into a prootic and an ex-occipital (/>''.o., e.o.) ; the foramen 

 ovale (V.) is not quite enclosed by this bony tract. Below (fig. 7), the bone only leaves 

 a scooped cartilaginous space, margined by a bony balk, for the pedicle {2^d-) <iiid a 

 small tract running from the setting on of the stylo-hyal {st.h.) to the fenestra ovalis 

 (st.). The liinder third of the interorbital space is cartilaginous, and the large optic 

 fenestra (II.) occupies its middle. That region is almost oblong — it dilates a httle 

 at both ends ; it is only three-fiftlis the width of the sub-oval orbital spaces. Tlie 

 single fenestra is long-heart-shaped ; the fore end of it has been filled in by periosteal 

 growths from the girdle-bone ; the lateral tegminal growths are wide. This is a very 

 rare ethmoid; its superorbital region is unossified, and grows out and back into a narrow 

 cartilage with a sinuous outhne ; this process carries a distmct oval superorbital (s.oh^.) 

 which is turned forwards. This free cartilage occurs again in PhyUomedusa and Ahjtes 



