OF THE SKULL IN THE AMPHIBIA UEODELA. 189 



In this chondrosteous skull the exoccipital (PI. XIX. figs. 1 & 2, e.o.) runs over the 

 epiotic and opisthotic regions, reaching the fenestra ovalis helow (fig. 2, fs.o), and 

 covering the arch of the posterior canal (fig. 1, p.sc.) ahove. 



An ohlong haud of cartilage finishes the roof and the floor of the occiput (s.o, b.o) 

 and these tracts pass further forwards into right and left tracts of cartilage that inter- 

 vene between the exoccipitals and the prootics (pro). These latter bones are less deve- 

 loped above than below ; above, they skirt the fore margin of the auditory mass, and 

 then leave the arch of the horizontal, and the ampulla of the posterior, canal unossified 

 (fig. 1, h.8C,p.sc). Below (fig. 2), the bony tract has grown to the outer margin, but 

 the vestibule is soft ; thus the fenestra ovalis has half its rim unossified. The 9th and 

 10th nerves (9, 10) are well enclosed in bone, which, as usual, runs between them. 



The position of the fenestra ovalis (the stapes was lost in dissection) is postero- 

 external. The sphenethmoids (sp.e) barely harden half the intcrorbital walls ; they reach 

 neither to the nasal region in front nor to the optic foramen behind ; thus the whole 

 alisphenoidal region and the hind part of the orbitosphenoidal is unossified (fig. 2) ; 

 so, also, is all the nasal region, which is floored by very large leafy trabecular cornua 

 (c.tr), and bounded behind by the ethmo-palatine cartilages (e.pa). 



The condyles of the suspensorium look forward and reach nearly to a line drawn 

 across the optic nerves (2) at their exit; there is a quadrate bone (q), which, however, 

 does not ossify half the cartilage. The otic process (ot.p) is not hidden by the pterygoid 

 bone, but the pedicle is. This species agrees with the Menopome in having that bone 

 (fig. 2, p.pg) divided from the palatine. It is a curious sort of small hatchet, with a 

 rounded blade that binds upon the inner face of the suspensorium, and a haft which is 

 bent outwards, and ends in a sharp point in front, which has no teeth on it. The large 

 vomers (p) are perfectly larval, and are confluent with the small palatines ; they meet in 

 front, and then form an elegant arch, whose anterior margin carries teeth. The inner 

 end of each bone is rounded, and the outer sharp, the sharp end overlapping the pterygo- 

 palatine. Just in front of the middle of each plate there is a rounded inner lobe. 



This arch is behind the large flabelliform cornua trabecule. In front of those lobes 

 there is a larger dentigerous arch, very elegant and forming nearly a semicircle. All 

 except the extremities of this bone is formed by very large premaxillaries ( px), the ends 

 by small maxillaries (mx). As in Proteus, Menobranchus, the Siren, Menopome, 

 Axolotl, and Spotted Salamander (Pis. XIV.-XVL), there are two premaxillaries ; but 

 most of the Caducibranchs have but one, as in the last two instances. 



The nasal process of each bone is slender, and the palatal edge of each bone is 

 ■narrow ; the maxillary (mx) is a small style attached to each outer end. The nasals 

 (fig. 1, n) are oblique lozenge-shaped bones, pointed in front, and to a less degree 

 behind ; the nasal processes of the premaxillaries rest on them, they on the frontals (/), 

 and the frontals on the parietals (p), by a normal regular imbrication. 



A conchoidal ectethmoid (e.eth) flanks each nasal, and also partly the outer edge of 

 the frontal. The interorbital region of the skull being very long, the frontals and 

 parietals are very long and narrow ; the latter run far forwards as a wall-plate to the 

 skull, and are largely overlapped by the frontals. 



SECOND SERIES. — ZOOLOGY, VOL. II. 26 



