DEVELOPMENT OF THE SKULL IN THE URODELES. 179 
differ rather in size than in form and parts, I shall anticipate what is said of the lesser 
skull in this comparison. 
The whole series of investing bones are singularly alike in these two types; but in 
Sieboldia there is no small bony plate in the mid line in front, such as we see in 
Menopoma (Pl. XX XVIII. fig. 1). 
In this large kind, in age, the premaxillaries are ankylosed to the maxillaries, the 
pterygoids to the quadrates, and the parasphenoid to the exoccipitals. 
The shape of the skull is very similar; but the larger skull is very unsymmetrical, 
the right side being the larger of the two; the /eft vomer, however, is the larger bone. 
In both, the palatines and vomers have recombined subsequent to the throwing off 
by the former of the bony pterygoid; in both that bone uses up all the proximal part 
of the pterygoid cartilage. 
The columelle (pharyngo-hyals combined with the stapedial plates) are marvellously 
alike in both ; but the /eft has coalesced with the suspensorium in the large kind. 
The epihyals are free in Sieboldia, and confluent with the suspensorium in Meno- 
poma; in the latter the three pairs of hypohyals and the basal piece are free ; in the 
large kind the first and second hypohyals are confluent, right and left, with the basihyal. 
This large kind and the Menopome come very close in their structure to the common 
Newt when its gills are almost gone; but whilst in the American species the gill- 
arches are all retained, and become more or less ossified, in this Japanese species the 
third and fourth are absorbed, and the first loses its upper segment, and remains 
unossified. I have no doubt that careful dissection of the /aryna would show some 
rudiment or rudiments of the distal end of the second basibranchial; but I have only 
figured them as they existed in the Menopome (PI. XXXIX. fig. 4, t.hy, lx). I had not 
the opportunity of dissecting these parts in the large kind. I may remark, however, 
that in old age that bar becomes largely absorbed in T’riton cristatus (Pl. XLI. fig. 7) ; 
but some part of the end of the bar is generally retained in the Urodeles, whose 
“thyrohyal,” as in birds, is made out of a median or azygous piece, and is not symme- 
trical as in the Anura. 
It is worthy of remark that in this kind, as in the Menopome, the pterygoid cartilage 
is largely developed; it is arrested in Proteus, Siren, and Menobranchus, which resemble 
early larve of the “ Caducibranchs ;” and also that the broad proximal end is afterwards 
absorbed. 
I call its remnant the “ epipterygoid ” cartilage, under the impression that this piece, 
ennucleated, so to speak, in these types, breaks out again in the Lizard, and has all 
but an isthmus of its basal part suppressed in the Chelonia’. 
1 See my paper on the Lacertian skull (Phil. Trans. 1879) and on the Chelonian skull (‘ Challenger’ series, 
vol. i. pl. x.): in the Lizard it is a long, distinct rod of cartilage, suberect on the pterygoid bone; in the 
Turtle it is less erect, smaller, and hangs on the “pedicle” of the mandibular pier, from which it becomes 
segmented afterwards, when it ossifies. I begin to see the meaning of the remnants of the Ichthyopsidan 
suspensorium that break out again in the Sauropsida. 
VOL. X1.—Part vi. No. 2.—January, 1882. 25 
