in Hat-
teria;
448
piece (fig4). TFrom seven to nine of these ribs have ossified
sternal ribs which serve to connect them with the sternum.
The lumbar vertebrae have only ng
long transverse processes which
arise above the neuro-central
suture. The sacral vertebree
support very stout transverse
processes, each of
which includes a rib
element and becomes
anchylosed to the
centra only at a late
period of life, as do ¢
ne ns
= S
the comparatively
long and slender
caudal transverse
processes. Inferior ==
Prockenes, .]Ly pers Fr16. 4.—Lateral asp7e'gt of three thoracie vertebroe
physes, which are of ¢rocoditus vulgaris (from nature). ¢, cup on the
anterior surface of centrum ; ¢p, capitula of ribs;
azygous, descend one ns, neural spines ; ¢, rib cartilag’es; ¢, tubercula of
from Dbeneath the ribs; u, uncinate processes; vr, vertebral ribs.
centrum of each of the more posterior cervical and anterior
dorsal vertebrze.
The sternum consists of an ossified rhomboidal plate,
with the hinder side of which two pairs of costal cartilages
articulate. A narrower piece extends backwards from
this plate (connected with it by ligament), and ends in two
diverging processes. With this the other sternal ribs
articulate. A long slender bone, the interclavicle, or
episternum, lies in a median groove of the sternal plate,
and extends forwards beyond it.
There is a so-called abdominal sternum made up of a
series of seven or eight slender bones which lie in the
aponeurosis of the external oblique muscle of the abdomen
behind the true sternum and in front of the pelvis. It
lies at a lower level than the sternum, and has no direct
connexion with the vertebral column.
In Hatteria, the only living member of the order
Rhynchocephalia, as well as in the extinct species, the
vertebral bodies have flat or concave surfaces in front and
behind. There are 8 cervical, 14 dorsal, 3 lumbar, 2 sacral,
and 36 caudal vertebree. There is no persistent neuro-
central suture in Hatteria, though there may be in some
extinct forms of the order. Rudiments of the proatlas are
sometimes present. The atlas consists but of three pieces,
and the odontoid bone is anchylosed with the atlas, and
is concave anteriorly. An autogenous hypapophysis is
wedged into the inferior interspace between the centrum
of the axis and the third vertebre, and similar parts are
developed thence backwards to beneath the seventh and
eighth vertebree. ZHatteria has the faculty of reproducing
its tail after mutilation. When the tail is broken the
fracture takes place in the middle of one of its centra and
not between two adjacent centra. This is owing to the
fact that each caudal vertebra is divided into an anterior
and a posterior part (fig. 5), :
and is weakest at this line of
junction which passes behind
the transverse process.
The first rib is attached to ‘
the fourth vertebra. Those Fie. 5.—Vertical section of four (7th
of the ninth and the following ;%yls?;il) Ee dglasl fée"é ";:ou;]‘; e
vertebre attain the sternum. middle of centrum. (After Giinther.)
The more posterior ribs become connected with the abdo-
minal sternum. All the ribs are single at their proximal
ends, a bifurcation being scarcely indicated even at the
most anterior one. Processus uncinati are fully developed.
The sternum is a rhomboidal, semi-cartilaginous plate,
with a medianly situated long and slender episternum which
unites with a pair of clavicles. An abdominal sternum is
hERIT I LHES
[ANATOMY,
more fully developed than in any other living Reptile. It
consists of about twenty-five transverse rods, each of
which is composed of three pieces. These rods are con.
nected and disconnected with the ribs in an alternate
manner, every other rod being suspended from a pair of
the true ribs.
Lacertilia.—In this extensive order of living Reptiles
Uropeltide, where they are biconcave. There may or may
not be distinct cervical, lumbar, and sacral regions, and the
number of vertebre, generally considerable, may be very
large. The distinctness of the vertebral regions depends
on the development of the anterior and posterior limbs.
When a cervical region can be distinguished, there are
never more than nine such vertebre. Only in rare
instances are there distinct lumbar vertebrse. The sacral
vertebree are never more than two. The neural arch is
always anchylosed to the centrum in adults. The atlas
consists of three parts, and the axis may or may not have
the odontoid bone anchylosed to it and convex in front.
Ribs are attached to most of the cervical as well as to the
dorsal vertebree ; but the former are not expanded distally
as in the Crocodile, and thus the latter do not support
uncinate processes. The more anterior ribs show two
proximal articular surfaces, but these never diverge into
distinct capitular and tubercular processes as in the Croco-
diles, nor, as in the latter, do any of the dorsal vertebra
develop double, superimposed transverse processes. The
more anterior (usually the first three or four) dorsal ribs
are connected with the sternum by sternal cartilages,
Those behind may be similarly connected with the diverg-
ing backward prolongations of the sternum, or may be
directly connected with their fellows of the opposite side,
as in the Chamzleon, a median cartilage being joined on
either side by the sternal cartilage continuous with an
ossified rib. In Acontias and other limbless Lacertilians
which have but a rudimentary sternum, or none, the corre-
sponding ribs of the right and left sides are connected
across the mid-ventral line as they are in Chamaleo. In
Draco the more posterior ribs are greatly prolonged, and
their distal cartilages are bent backwards. This is to
enable them to support the wing-like membrane which
extends from either side of the body to serve as a
parachute. In those Lizards which have a lumbar region,
transverse processes are there developed. The caudal
vertebree (except the most anterior and the small posterior
ones) have chevron bones, which are not generally anchy-
losed to the vertebrse which support them.
In addition to the ordinary articular processes, there are
in Iguana certain accessory articulating structures such as
are commonly found in the vertebrae of Serpents; these will
be described in the next section.
The sternum consists of a rhomboidal semi-ossified or
cartilaginous plate, which is sometimes continued back-
wards into a pair of long diverging processes. There is
generally an episternum, which is often T-shaped, but it
may be absent, as in Chamaleons. In the limbless Lizards
the sternum is cartilaginous, and there is none whatever in
some forms, as, e.g., in Amphisbena and Typhline.
In many Lizards, notably in the commonest English
Lizard, the tail if broken off can be reproduced. In them
the centra of the caudal vertebrse have a vertical median
division similar to that already described in Hatteria.
In Ophidians the number of vertebree is generally very in 0
large, and may exceed four hundred. They are all proccel- dian:
ous, and the ball behind each is nearly hemispherical. There
is no distinction of cervical, lumbar, or sacral vertebra ;
but all the vertebra after the atlas may be considered as
either dorsal or caudal. The mode of articulation between
the vertebree is more complex than in almost any Lizards.
: 2 in L}
the vertebree are proccelous except in the Geckotida ané tilia
