OF THE SKULL IN THE UKODELOUS AMPHIBIA. 
577 
each side, adhering to the trabecula, its point in front, and its notched base behind 
(fig. 2, v., pa.). This little crop of teeth is being attached to an undergrowth of bone- 
cells ; the antero-external part is vomerine, and the postero-internal part palatine ; they 
arise, however, as one single upgrowth of pointed, recurved papillae, that rapidly become 
denticles. 
In such a skull the main nerves are easily seen (figs. 1 & 2 ; 5,7, 9, 10) ; their size, 
relations, and distribution are precisely like those of Menobranchus (Huxley, op. cit.) 
and those I have just described in Siredon. 
The postmandibular visceral arches are conveniently studied as a separate object in 
this micro-morphological work. 
The upper, or hyo-mandibular element never appears in this species ; the lower cornu 
(fig. 3, c.hy., h.hy.) is a flattish sigmoid bar, which is blunt-pointed after it has become 
broad above. Below it is more terete, and a short distal segment, the hypohyal, is 
evident ; each hypohyal is attached by a ligament to the fore end of the first keystone 
piece of the branchial apparatus. 
There are four branchial arches, the last gill-less, and these are conjugated by two 
azygous pieces (fig. 3, hr. 1-4, h.hr.). 
These bars rapidly lessen backwards, and the hinder two are unsegmented ; the seg- 
ments in the front two are a short ceratobranchial (c.hr.) and a long epibranchial ( e.hr .); 
the last two have no ceratobranchial part or region, and are carried on the third. Both 
the ceratobranchials articulate with the first basibranchial, which is twice as large as 
the second or free hind piece [h.hr. 1, h.hr. 2). 
Last Stage. The Skull of the adult Seironota perspicillata. 
The changes through which this larval skull has passed must be conceived of as 
essentially like what I have described in going through the various stages of Siredon to 
that of Amhlystoma. 
If not in this, yet in several others, I have traced every important change. 
The general form of the adult skull is oval as to outline and very flat, and is no larger 
than a “Ladybird”; it is yet a very finished structure, and represents, very fairly, the 
culmination of the Caducibranchiate type of skull. Each bone, like the composite 
cranium, has its own perfectness. 
The three capsular regions are almost of equal length (Plate 29. figs. 4, 5, 6) ; the 
optic is modified, in the Urodele, mainly as a recess ; the nasal roofs are cartilaginous 
and almost entirely hidden by outer bones ; but the auditory sacs are the largest, 
are densely ossified, and freely exposed. 
The occipital arch is strong and largely confluent with the ear-masses ; above, its two 
bony halves meet and unite by an irregular, short, superoccipital suture, which is some- 
what overlapped by the parietals (fig. 4, e.o.,p.). 
Below (fig. 5) there is a wider space between the two half-rings ; and in this synchon- 
drosis there is no visible trace of the notochord and its evanescent vertebral segments. 
MDCCCLSXVII. 4 M 
