Some few Lacertilia
, like the Chamaeleons
and the Amphisbaence,
are covered by a soft integument;
but, in the majority, there is an epidermic exoskeleton
composed of homy plates, tubercles, or spines, or overlapping
scales. In some forms (e. g., Scincus, Cyclodus
) the dermi
beneath the horny scales is ossified, and the body has a complete
armor of bony scutes, corresponding in form with the
scales. The dermal ossifications of the head may coalesce
with the subjacent bones, but this union of dermal bones with
subjacent parts does not occur in other parts of the body.
The spinal column always contains a considerable number
of vertebrae; and, except in the Amphisbaene
and some few
other Lizards, the tail is long. Those Lizards which possess
hind-limbs have a sacrum, into which not more than three
vertebrae, and rarely more than two, enter. The presacral
vertebrae are distinguishable, when sternal ribs are present, into
cervical and dorsal. All those vertebrae which lie in front of
the first sternal rib are cervical; and if, as sometimes happens,
the last two or three dorsal vertebrae are devoid of ribs, they
become lumbar. Not more than nine vertebrae are met with
in the cervical region of existing Lacertilia
, and this number
is rare. The number was greater in some extinct Lacertilia
The atlas is composed of three pieces, one inferior and
two superolateral. The odontoid bone is closely united with
the second vertebra, and its anterior face may be cylindroidal.
A separate ossification is sometimes formed on the under-surface
of the spinal column at the junction of each pair of vertebrae.
Such a separate ossification, or sub-vertebral wedgebone
is commonly developed beneath and between the odontoid
bone and the body of the second vertebra.
The centra of the vertebrae are either procoelous, or amphicoelous;
the former being by far the more common condition
in existing Lacertilia
, all of which, except the Geckos and Sphenodon
, have procoelous vertebrae. The cups and balls
are usually ellipsoidal, the long axis of the ellipsoid being
transverse. In the Geckos, the centra of the vertebrae are
conically excavated at each end; and, except in the centre of
each vertebra, where it is ossified, the notochord persists
throughout the spinal column.
The sacral vertebrae of existing Lacertilia
are not anchylosed
together, nor are their articular faces modified, the two
being connected by a free cup-and-ball articulation. The
movements of the two vertebrae, however, are restrained by
the strong ligaments which connect their neural spines and
arches, and by the fibro-cartilage which connects and covers
the free ends of their expanded ribs.
In the anterior part of the tail of the Lacertilia
usually well-developed subvertebral chevron bones, which are
commonly attached to the bodies of the several vertebrae, and
not in the intervals between adjacent vertebrae. In many Lacertilia
(Lacertae, Iguanae, Geckos
) the caudal vertebrae
have a very singular structure, the middle of each being traversed
by a thin, unossified, transverse septum. The vertebra
naturally breaks with great readiness through the plane of the
septum, and when such Lizards are seized by the tail, that
appendage is pretty certain to part at one of these weak
The arches of the vertebrae of the Lacertilia
together by the ordinary oblique processes, or zygapophyses
In the Iguanae
. they are additionally connected by a process
of the front part of each arch (zygosphene
), which fits into a
fossa on the posterior face of the preceding arch (zygantrum
These Lacertian vertebrae thus nearly approach the vertebrae
of the Ophidia
The transverse processes of the vertebrae are very short,
and are, at most, divided into two indistinct facets, with which
corresponding facets on the proximal ends of the ribs articulate.
|Fig. 69. - The skull of Cyclodus, entire and longitudinally bisected.
Ribs may be developed in all the cervical vertebrae except
the atlas, and they usually increase in length toward the dorsal
region, where more or fewer of them become connected
with the sternum. The dorsal moiety of the primitive cartilage
of the rib becomes ossified, and the primitive cartilagebone
is finally replaced by membrane-bone. The ventral moiety
becomes converted only into cartilage-bone, and may pass
directly and without articulation, on the one hand into the
sternum, and on the other into the vertebral rib. Processes
are sometimes developed from the posterior margins of certain
of the ribs, which are termed processus uncinati
. The sternum,
when fully formed, consists of a rhomboidal anterior portion, from the posterior angle of which a single, or double,
backward prolongation is continued into the wall of the abdomen.
Two or three pairs of the sternal ribs are connected
with the posterolateral edges of the rhomboid, while the rest
may be attached to the abdominal prolongations; or, behind
these, they may be continued into one another, to form complete
hoops across the wall of the abdomen (Geckos, Chamaeleons,
The Flying Lizard (Draco volans
) is remarkable for the
elongation of many of its posterior ribs, which are continued
into, and support, the parachute-like expression of the integument
by which it is enabled to perform its flights.
The skull of the Lacertilia
resembles that of the Chelonia
in the development of an interorbital septum (except in the Amphisbaenae
), and in the absence of alisphenoids, or of any complete ossification of the presphenoidal or orbito-sphenoidal
regions. The premaxillae and maxillae are firmly united with
one another and with the skull, and there are two vomers. An
unossified space, the parietal foramen
, usually remains in the
roof of the skull in the course of the sagittal suture, or between
the parietals and the frontals.
In the principal group of the Lacertilia
, a column-like
membrane-bone, called the columella
(but which is not to be,
by any means, confounded with the stapes
, to which the same
name is often applied in Reptiles), extends from the parietal
to the pterygoid on each side, in close contact with the membranous
or cartilaginous wall of the skull. Hence they have
been called "Kionocrania,"
or "column skulls." This columella
(Fig. 69, Co
) appears to correspond with a small independent
ossification, which is connected with the descending
process of the parietal and with the pterygoid, in some Chelonia
In the great majority of the Lacertilia
(as in the Chelonia
the side-walls of the skull, in the region of the ear, are produced
into two broad and long parotic
processes, into the composition
of which the opisthotic, ex-occipital, and prootic
bones enter. Each quadrate bone is articulated with the outer
end of one of these processes (in which a small separate pterotic
ossification sometimes appears), and is usually movable.
The parietal bones do not unite suturally with the occipital
segment of the skull, or with the prootic bones, but are connected
with them only by fibrous tissue. And as the presphenoidal region remains unossified, or incompletely ossified, it
follows that the fronto-parietal portion of the skull is, in most
Lizards, slightly movable upon the occipito-sphenoidal part.
Each parietal bone is prolonged backward into a process
which articulates with the upper part of the parotic prolongation
of the skull; and to the outer side of the posterior extremity
of the parietal process the squamosal is attached. The
squamosal may be continued forward to the post-frontal, which
is sometimes subdivided into two. The post-frontal may unite
below with the jugal, and thus bound the orbit. Only in Sphenodon
, among recant Lizards, is the jugal connected with
the distal end of the quadrate by bone. As a general rule, the
quadrato-jugal is represented only by a ligament.
In consequence of the structure which has been described,
the posterior region of the ordinary Lacertilian skull presents
a number of distinct fossae in the dry state. A supra-temporal
fossa lies between the parietal, the post-frontal, and the squamosal,
on the upper face of the skull; a post-temporal
the parietal, the occipital, and the parotic apophysis on the
posterior face; a lateral-temporal
, between the squamosal and
post-frontal above, the jugal and quadrate in front and behind,
and the quadrato-jugal ligament below.
The palatine and pterygoid bones are firmly connected both
with the facial bones, and with the floor of the skull. Thus
the basisphenoid gives off two basipterygoid
outer ends of which articulate with the inner sides of the pterygoid.
The posterior ends of the pterygoids are usually connected
with the inner surfaces of the distal ends of the quadrate
bones. Their anterior ends are firmly united with the
palatines; and, from the junction of the two, a transverse
bone (Fig. 70, Tr
) usually passes, to unite the palatine and
pterygoid with the maxilla.
The anterior ends of the palatines unite with the maxillae
and the vomers; but, in existing Lacertilia
, they do not meet
one another, or come into contact with the basisphenoid or
presphenoid in the middle line. The palatine apertures of the
nostrils are placed between the palatine bones, on the outer
side, and the vomer, on the inner. In only a few Lacertilia
do the palatine bones send down processes which bend toward one another in the middle line, and so form a posterioi
nasal passage, partially separated from the oral cavity.
|Fig. 70. - Under-view of the skull of Cyclodus: N posterior nasal aperture
The two rami of the lower jaw are
usually, though not invariably, firmly connected
at the symphysis-and each is
composed of five ossifications in addition
to the articulare
The hyoidean apparatus consists of an
elongated median rod, the anterior part
of which supports the base of the tongue;
and, usually, of two long cornua on each
side of this. The cephalic ends of the anterior
cornua may be perfectly free, and
lie upon the sides of the neck, as in Psammosaurus
; or they may be traceable to,
and be connected with, the stapes and
the parotic processes, as in Sphenodon
The limbs may be completely developed; or only one pair (either the anterior
or the posterior) may be present;
or they may be entirely absent. When
present, they may be mere styliform rudiments,
or may possess any number of digits from two to five. Even when the
limbs are altogether absent, the pectoral
arch remains, though the pelvic arch seems to vanish. When the pectoral arch
is complete, it consists of a suprascapula,
scapula, coracoid (with precoracoid and epicoracoid elements),
and two clavicles, united by an interclavicle, which lies in a
groove of the sternum. (Figs. 12 and 13, pp. 35 and 36.)
The coracoids articulate with grooves in the anterolateral
edges of the sternum, and usually more or less cross and overlap
one another, in front.
In the genus Lialis
, in which not a trace of a fore-limb is
discernible, there is a small sternum, consisting of a flat,
somewhat pentagonal, plate of cartilage, in which there is a
little coarsely-granular calcareous deposit; but this sternum
is connected with no ribs, nor, though it lies between the
coracoids, does it articulate with them. Each coraco-scapular
arch is a continuous cartilage, narrow in the middle, but expanded
at its dorsal, and still more at its sternal end, where
the right overlaps the left, and both are connected by fibrous
tissue with the sternum. The narrow middle part of the coracoid is invested, and in part replaced, by a sheath of membrane bone,
which expands above and below, and represents both
scapula and coracoid, though it presents no trace either of
division, or of a glenoidal cavity. Beyond the extremities of
this central ossification the cartilage merely presents scattered
granular calcification. Along the front edge of each coracoscapular
arch, and closely connected with its ossified part, is a
long curved clavicle, entirely composed of membrane-bone,
and united with its fellow in the ventral median line, by ligamentous
fibres. There is no interclavicle. The pectoral arch
in other snake-like Lizards, such as the Blind-Worm (Anguis
and the Sheltopusik (Pseudopus
), is in much the same condition
as in Lialis
When the hind-limbs are well developed, there is a complete
pelvis. The ilia are movably articulated with the fibrecartilages
which cover the ends of the sacral ribs. The pubes
and the ischia meet in median symphyses, and the anterior margin
of the pubis usually, as in the Chelonia
, gives off a strong
curved process. In many Lacertilia
a partially-ossified or cartilaginous
rod (os cloacoe
) is continued back from the symphysis
of the ischia, and supports the front wall of the cloaca.
In most Lacertilia
the manus possesses five digits; and,
when this is the case, there are usually eight bones in the
carpus-one for each metacarpal on the distal side, one radial,
one ulnar, and one central. As a very general rule, the pollex
has two phalanges, the second digit three, the third four, the
fourth five, and the fifth three (2, 3, 4, 5, 3). The pes, also,
generally possesses five digits, which increase in length to the
fourth, the fifth being smaller than the rest, and divergent in
direction. Two large bones, very closely united, or completely
fixed together, represent the calcaneum and the astragalus,
and are articulated, in a manner which allows of very little
motion, with the tibia and fibula. In the distal row there is
usually a large bone, representing the cuboid. The fifth
metatarsal (The bone thus named may perhaps contain a tarsal element, and represent
not only the fifth metatarsal, but the corresponding distal tarsale
.) is bent, as in the Chelonia
, and may articulate with the calcaneum as well as with the cuboid. One or two
of the cuneiform bones may be present, or the inner ones may
be represented merely by fibrous membrane, or by cartilage;
in which latter case the inner metatarsals appear to articulate
directly with the astragalus in the skeleton. The number of
the phalanges is very generally the same as in the manus for
the four tibial toes, but one more for the fibular (2, 3, 4, 5, 4).
The Lacertilia all possess teeth, which may be confined
to the premaxillae, maxillae, and dentary piece of the mandibles; or may, in addition, be developed on the palatine and
pterygoid bones. These teeth are simple in structure, and
their crowns have very various forms, being sometimes sharp
and conical (Monitor
); or blade-like, with serrated edges
); or with broad, crushing, and spheroidal crowns
). As a general rule, the teeth become anohylosed
to the adjacent bone with age; and in the upper and lower
jaws they thus become attached, either by their sides to the
parapet of the jaw, when the dentition is said to be pleurodont;
or by their bases to the summit of the parapet, when
the dentition is acrodont
. The extinct Protorosauria
said to be thecodont,
or to have the teeth lodged in alveoli.
New teeth are usually developed at the bases of the old ones.
The Lacertilia are divisible into numerous groups, the leading distinctive
characters of which are exhibited in the following table:
I. - The pterygoid and quadrate bones united.
- A columella and an interorbital septum in the skull.
- Amphicoelous vertebrae (K. Amphicoelia).
- Dentition acrodont or pleurodont.
3. Homoeosauria (The columella has not been observed in these groups.)
- Dentition thecodont (?)
4. Protorosauria. (The columella has not been observed in these groups.)
- Procoelous vertebrae (K. procoelia).
- Not more than nine cervical vertebrae.
- The nasal bone, single.
- The nasal bones, two.
- The integument of the head not
covered with epidermic plates.
- The integument of the head covered
with epidermic plates.
- More than nine cervical vertebrae.
10. Dolichosauria. (The columella has not been observed in these groups.)
- No columella; no interorbital septum.
II. - The pterygoid and quadrate bones united.