DEVELOPMENT OF THE SKULL IN THE TJEODELES. 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 tj'pes ; but in 

 Sieloldia there is no small bony plate in the mid line in front, such as we see in 

 Menopoma (PI. XXXVIII. fig. 1). 



In this large kind, in age, the preinaxillaries 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 left 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 columella (pharyngo-hyals combined with the stapedial plates) are marvellously 

 alike in both ; but the left has coalesced with the suspensorium in the large kind. 



The epihyals are free in Sieloldia, and confluent with the suspensorium in MenO' 

 jpoma ; 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 moi'e 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 larynx 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, Ix). 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 Triton cristatus (PI. 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 larvse 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^. 



' See my paper on the Lacertian ekuU (Phil. Trans. 1879) and ou the Chelonian skull ('Challenger' series, 

 vol. i. pi. 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 liangs 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 Ichthyopsidaa 

 Buspensorium that break out again in the Sauropsida. 



VOL. XI. — p.tRT VI. No. 2. — January, 1882. 2^ 



