DEVELOPMENT OF THE SKULL IN THE URODELES. 175 
the jaw. The splenial (sp/) is smaller, but large also; it reaches, as in Menopoma 
(Pl. XXXVIIL. fig. 3, spl), nearly to the angle, inside; it carries teeth along its fore 
half, and is thin all the way, ending a little behind the symphysis, where Meckel’s 
cartilage (mh) is exposed. 
B. The Endocranium of Sieboldia. 
The chondrosteous inner skull of this species is very massive; about half of the 
cartilage of which it was composed is ossified. It is much hidden by the investing 
plates; but its parts are largely traceable notwithstanding. 
The occipital arch is like a low hour-glass, the foramen magnum (Pl. XXXVII. 
fig. 2, 1p m) is circular below and narzrow above; it has cartilage bounding it in both 
places. The condyles (oc. c) are large, oval, and look obliquely inwards and backwards ; 
between them, in the opening, there is a concave joint for the odontoid rudiment. 
Where the cincture is pinched in, there we see a common passage for the ninth and 
tenth nerves (fig. 1,1x, x). Each exoccipital bone (¢.0) just faces the capsules of the ears 
with a hollow bony plate, answering (partially) to both the opisthotic and epiotic. 
Above, the supraoccipital synchondrosis is covered with the parietals (Pl. XXXVII. 
fig. 2, p); below, the basal cartilage is floored with a compound plate, formed by 
fusion of the parasphenoid with the exoccipitals. 
In front the prootics (Pl. XXXVI. fig. 1, pr.o) occupy a rather small part of the 
front face of the capsules, which are unossified to a great degree across their middle 
part; in the postero-external face below we see the large oval stapes (PI. XXXVIT. 
figs. 1, 2, st), which is ossified and ossifies half the columella (p.hy). The shallow cranial 
barge has its low sides ossified in the orbital region; each bony tract, or sphenethmoid 
(sp.e), runs halfway from the optic to the oval foramen (m1, Vv), and runs three fourths of 
the way to the wings of the ethmoid, where it stops abruptly. 
The actual roof and floor are extraneous; for the “tegmen cranii” only exists as a 
rudiment before and behind, and the basal plate (parachordal passing into pro- 
chordal) is in two widely separated moieties; in front the “ intertrabecula” only 
exists as an internasal conjugation. 
The nasal region (a) is unossified; it is very broad, is confluent with the dilated 
cornua trabecule, the form of which has been transferred to the vomero-palatine bones 
(Pl. XXXVIL. fig. 1, v.pa). In front the premaxillaries fill in the large semicircular 
notch between the cornua and the nasal roofs. In the angle between the maxillary and 
prefrontal each nasal roof is exposed ; it is gently convex, and has an elliptical shape ; 
it does not reach the maxillary, the dyke between is filled up with a fibrous mat. 
c. The Visceral Arches of Sieboldia. 
Behind, the nasal sacs appear larger than they actually are; for the large, thick, 
arcuate ethmopalatines (¢.pa) haye followed their curve, and are confluent with their 
