850 AMPHIBIA.
The 1st vertebra has the usual two lateral facets, Plate LXXVIJ3, fig. 1 a a, for
articulation with the occipital condyles with an odontoid-like process (ft), similar to
that figured by Mivart1 in Amphiuma, fitting into an articular surface between the
occipital condyles. In one specimen, the parasphenoid sent up a sma.ll nodule
between the posterior margins of the exoccipitals and entered into the middle of the
anterior margin of the cavity. In this instance, fig. 2, the intereondyloid process of
the atlas was divided into two rounded articular facets b, which corresponded to two
median articular surfaces, fig. 25 s, internal to the facets of the condyles. I have
observed this arrangement in two cases. In specimens in which the odontoid-like
process is not very long, either one or both of the lateral facets of the 1st vertebra
are confluent with it, but, when it is of moderate size, each surface is sharply
defined. The spinous process of the 1st vertebra, fig. 3 c, has its extremity dilated
and covered with a broad rough porous plate (h) or crest corresponding to the
porous glandular layer of the back, and a sharp anterior edge (d) and a deeply
concave posterior surface (e) for the reception of the spinous process of the 2nd
vertebra. In the succeeding vertebrse, figs. 6 to 15, the spinous process becomes
much laterally compressed, and the lateral margins of the posterior concavity,
figs. 8 g and 12 g, become distinct plates, from which the posterior zygapophyses ( f )
depend.
The most peculiar feature of the vertebrse is the existence on the summit of the
spinous process of the dorsal, sacral, and first two or three caudal vertebrse of the
rough osseous expansion or crest, already referred to, and conforming to the outline
of each process, and which appears to be peculiar to this newt. I t is pointed anteriorly
and bifurcate posteriorly for the reception of the anterior extremity of the
process immediately behind it. The anterior and posterior zygapophysial facets
have the general characters of these structures in the Urodela. There are no hypa-
pophysial ridges in the trunk vertebrse. Transverse, processes are not indicated in
the 1st vertebra (fig. 6), but a process of this nature bearing a rib (on and p\
figs. 7 to 14, is developed in each of the vertebrse from the 2nd to the 2nd caudal.
In the rest of the caudal vertebrse, the transverse processes, figs. 15 and 16Z, also
assume the general character distinctive of the Urodela. In the dorsal region the
two transverse processes, superior and inferior, are placed side by side in the usual
manner and united by their edges, each terminating in an articular surface for
the head and tubercle,, of the rib. The base of each process is deeply concave
posteriorly, and is perforated by a vascular canal, as in many other genera of
Urodela.2 In the caudal region, figs. 15 to 18, the transverse processes are short,
their vertical plates having a somewhat wavy margin connected to the anterior and
posterior articular processes by a long longitudinal lamella and by a ridge to the
posterior inferior margin of the hypaxial arch. There is so great a similarity at
first sight between the dorsal and ventral arches, that when a single caudal
vertebra is taken up, one hesitates at first to decide between the arches. In the
1 Proc. Zool. Soc., 1870, fig. 19, p. 277.
2 Mivart, I. c., p. 271.
3rd caudal, the transverse process becomes flattened from before backwards, and
the hypapophyses spring from it and from the centrum as a common base in a much
more perfect manner than occurs in the 1st caudal vertebra of Siren, as described
by Mivart.
The hypaxial arch, figs. 15 to 18 on and n, consists of a broad flat plate, with two
diverging processes posteriorly. In the 4th caudal vertebra, a prominent ridge is
developed on the anterior face of the plate, which is curved with its convexity
forwards; and this modification becomes more and more intensified, until at last,
in the middle of the tail, fig. 16 on, the ridge is converted into a broad thin laming
with two divergent plates, which serve to embrace the ridges of the arch behind.
The ribs.—*There are sixteen ribs, thirteen in the dorsal, one in the sacral, and
two in the caudal region. Each rib is supported on a double-headed transverse
process, and is capable of a certain amount of mobility. As the ribs are traced backwards,
the tubercular and capitular portions are less distinctly marked, as is also the
division of the transverse processes into dorsal and ventral sections. The ribs are
well developed in the five anterior vertebrse, and are moderately curved, but the succeeding
ribs are nearly straight. The proximal ends of the ribs, figs. 19, 20, are
flattened from before backwards, and each consists of a capitular and tubercular
process, separated from each other by a narrow interval, except in those in which
these parts tend to become confluent. A considerable process (figs. 19, 20, &c., p)
is developed on the posterior margin of each of the first five ribs. All of these rib
processes, with the exception of the first, terminate in the knob-like glands of the
side, and the free extremities of the remaining ribs end in the same structures' The
first rib lies under the scapula, and has no gland opposite to it. The sacral rib,
figs. 11 and 12 on, has such a strong resemblance to its transverse process that it
might be mistaken for such, and from its nature has of course no relations with the
lateral glands.
Scapular arch.—The scapular arch lies over the 1st rib and on the anterior fourth
of the 2nd between the 2nd and 3rd vertebrse. All the constituent bones are completely
united with one another. The coracoid element is a semicircular flattened
rather thick plate (fig. 41), separated from its fellow by the semi-osseous epicoracoid
flaps which overlap each other. The glenoid cavity is behind the line of the
scapula on the posterior and superior margin of the coracoid, and looks upwards,
backwards and outwards, and is triangular with its base upwards. I t has two
protuberant walls; but the upper and posterior margins are continuous with the
posterior margin of the coracoid, and scooped out into a . deep wide notch, closed in
the recent state by a strong membrane. The lateral margins are separated from
each other anteriorly by a narrow notch for the reception of the articulating ridge
of the humerus. There is a nerve foramen in the usual position in front of the
glenoid cavity and a deep notch at the base of the anterior angle of the scapula
and coracoid. The scapular element is slightly concave externally, and expanded
from below upwards terminates in a broad semi-osseous or cartilaginous supra-
scapula without any notch on its anterior angle.