The orbito-sphenoid (fig. 32) is a moderately elongated hone, with its inner side
smooth and concave, and its outer side transversely convex. I t is perforated near
its posterior extremity by a large foramen directed upwards for the transmission of
the optic nerve and by a small one immediately behind the former. The anterior
and upper extremity which forms the internal lateral margin of the internal nostril
is marked by two processes which enclose a rather deep groove. I t articulates with
the prefronto-lachrymal, exoccipital, parasphenoid, palato-vomerine, and parietals.
The temporal (fig. 85) is directed obliquely outwards and slightly backwards,
which partly accounts for the wide gape of this animal. I t rests on. the anterior
external angle of the auditory capsule and touches the parietal and the frontal
anteriorly, completing the upper margin of the arch of the orbit. Its anterior angle
receives the head of the pterygoid, which also rests on the process on the under side
of the auditory capsule external to the supposed orifice of the facial nerve. I t is a
hammer-shaped hone with a massive head projecting behind, consisting almost
entirely of the rough, hard, bony substance of the cranial crest.
The quadrate (fig. 35) is somewhat triangular, with the longest diameter of its
articular facet lying obliquely across the long axis of the temporal, concave outwards
and backwards, the face of the facet looking outwards and forwards. A prominent
process surmounts the hack of the facet, and a curved one is directed forwards for
articulation with the posterior end of the maxilla.
The pterygoid (fig. 36) consists of two parts, a body and a wing-like process
projecting forwards from its anterior margin. The body of the bone is applied to
the internal surface of the temporal and quadrate, and by its head to the auditory
capsule and to the inner side of the angle of union of the maxillary process and body
of the temporal.
The head consists of two parts corresponding to its articulations, an internal
and external. The former is hollowed out, and the cavity opens on the external side
of the neck of the hone, and is prolonged along the posterior margin of the body as
a well-defined short groove which is converted into a canal when the hone is in
position against the temporal which closes it below. A branch of the cavity is also"
prolonged along the wing as a groove in some skulls, and a canal in others, and when
the latter exists, it communicates with the head of the hone by a special foramen.
Superiorly the cavity is closed by the pterygoid process of the auditory capsule.
The anterior wing of the bone is hard and somewhat sickle-shaped, and is projected
forwards and outwards to touch the maxilla, when it sends backwards a narrow
shelf of bone from the inner margin of the internal nares.
The floor of the cranial cavity is almost perfectly straight (fig. 33), although
the outline of the skull is much curved; the curvature, however, is confined to the
roof which arches down over the anterior extremity of the parasphenoid until the
anterior margins of the frontals are brought nearly on a linn with that bone. A line
prolonged forwards from the parasphenoid would have the premaxillaries below it.
The extremities of the hyoid arch (fig. 40), when the mouth is closed, project
backwards and upwards behind the skull, on a line with the lateral cranial crest,
and both the ceratohyal and thyrohyal are free and covered by the forepart of the
paratoids. They are invested in a sheath of fascia and attached to the back of the
skull by a fine ligament, but they are not in’ contact with any of the bones of the
skull.
Dr. Strauch, the most recent writer on the value to be attached to the structural
differences manifested by the TJrodela, has sub-divided them into two great sections,
depending on the distribution of the palato-vomerine teeth, whether they are in the
longitudinal series Mecodonta, or in transverse more or less oblique series Lechriodonta.
This genus falls, therefore, under the Mecodont division, which includes, according to
Dr. Strauch, only Triton and five other genera, viz., tSalamcmdra, Bleu/rodeles,
Bradybates, Ghioglossa, and Salamandrina. To the first-mentioned genus, Strauch
refers a number of Amphibians, which have hitherto been considered by many
naturalists to represent generic types, e. g., Triton, Notophthalmus, JEuproctus, Cynops,
Taricha, Lophi/nus, and Ommatotriton; but if his view were accepted, Tylototriton, if
judged by its skull alone, would perhaps be regarded as only a form of Triton.
Strauch sub-divides the genus Triton into two sections, characterized by the absence
or presence of a fronto-temporal arch, as he does not consider the osseous bridge
formed by the frontal and temporal so important a structure as to let its presence
or absence determine a genus, and moreover, he has pointed out that Leydig has
shown that the form of the arch goes hand in hand with other organic similarities
of structure, with the exception perhaps of those which are sexual. The males,
however, of some species, for example, in which the fronto-temporal arch is wanting,
or merely indicated by a ligament, have at the breeding season a high crest, whilst
males possessing a well-developed arch may not have a crest, while others, such as
Ommatotriton vittatus, which Gray considered a very distinct genus, may have
a crest.
The differences existing between the skulls of the various forms of Amphibians
referred by Strauch to the genus Triton would probably be considered of generic
importance if they occurred in higher groups of vertebrates. In estimating the
value of skull characters in this group however, the consideration of the remarkable
changes which the cranium undergoes after the animal has left the egg has to be
borne in mind, as these changes would seem to indicate a greater capacity in the
skull of these Amphibians to variation than occurs in the skulls of other and higher
animals, which are not the subject of any remarkable modifications after birth.
Tylototriton, however, presents certain characters which seem to separate it gen-
erically from all other Mecodont TJrodela, more especially as they are associated with
other features which are not common to any other Amphibians. The skull characters
are the remarkable osseous crest which runs round the margins of the upper surface
of the skull and the shorter crest along the parietals, each of these structures being
deeply fitted for the reception of the remarkably large cuticular glandular pits
which densely stud the skin, and are always packed full of secretion, and a perfect
ptyergoid arch reaching the maxilla, the latter bone prolonged right up to the
quadrate, to which it is attached by a ligament. Associated with these characters