9 are regarded as proximal ends; and 10, 11 with less confidence are
regarded as distal ends from which the distal epiphysis has come
away. It is to be anticipated that the distal end of the tibia in
Pterodactyle will when found approximate to the distal end of the tibia
in the bird.
The bone is at the proximal end straight and sub-cylindrical, slowly
enlarging proximally; convex behind, except for an elevated boss some
little way below the proximal articulation for the attachment of
powerful muscles. In front the shaft is a little flattened proximally,
with a mesial groove dividing two prominences which are apparently
homologous with the ridges below the patella in birds. The proximal
articular surface truncates the shaft at right angles except at what
is regarded as the outer front aspect, where it rises into a small
patelloid prominence.
It shows the impressions of two condyles, which correspond in form with
the distal end of the Femur.
Nos. 3 and 6 are regarded as left tibia; Nos. 4, 5, 7, 8, 9 as examples
of right tibia.
No specimen likely to be a fibula has been found. In Dimorphodon and
in German Genera the fibula is Avian in form. The Crocodile offers
some approximation to the Pterodactyle shape in the proximal end of
the Tibia, but the Pterodactyle has Avian characters in addition. Its
straightness and length, ridges on the front and patelloid prominence,
are Avian.
TARSUS OR TARSO-METATARSUS.
Pl. 8.
Case. Comp. Tablet. Specimen.
=J= _b_ 13 1
This fragment, which may be the distal end of the bone corresponding
to that called in birds the tarsus or tarso-metatarsus, is badly
preserved. Yet so close is its resemblance in form, structure, and
apposition of the constituent bones to what obtains among birds,
that it may probably be identified as the tarsus; while the peculiar
characteristics of Pterodactyle bones which it shows, demonstrate that
it is not from a bird, but from an Ornithosaurian skeleton.
The bones are of paper thinness, and consist of a strong bone behind
which distally appears on the inner side to be compressed and thrown
backward and flattened at the side, exactly like the inner toe in
Natatorial birds. On the front of this strong support, confluent with
it, and confluent together, so that the places of union are only seen
at the distal end and in transverse section, are three bones, together
as wide as the bone on which they rest. It does not appear possible
that the distal articulations could have supported more than three
digits.
This bone, if correctly determined, offers points of affinity
with birds as pronounced and as important as any thing shown by
the extremities, for among reptiles a welding of the (tarsal or)
tarso-metatarsal bones is unknown, and here it is as absolute as in any
bird, and takes a characteristic bird shape. In the Rodent Jerboa the
metatarsus has much the same form as in a bird.
No phalanges have been recognised.
The Vertebral Column.
ATLAS AND AXIS.
Pl. 9.
Case. Comp. Tablet. Specimen.
=J= _c_ 1 1-15
Fifteen specimens are mounted to exemplify the structures of the
Pterodactyle atlas and axis. Nos. 1, 11, and 2 have already been
figured, and described by Prof Owen, the latter as a section of a
cervical vertebra.
The _atlas_ centrum, a saucer-shaped disk of bone, commonly united more
or less intimately with the centrum of the axis, but sometimes free. It
presents in front a hemispherical cup for the basi-occipital, and is
flattened or slightly convex behind. Its neural arch is seen in Nos.
2, 10, and 12; but the only specimen with the arch entire is in the
museum of James Carter, Esq. The neurapophyses vary in form and size,
but always are small obliquely flattened lamellar bones, which extend
upward and backward to meet the neural arch of the axis, just above the
neural canal, where a thin and small cross piece connects them together.
The distinctive aspect of these bones is given by the neural arch of
the _axis_, which is very much elevated, and is formed by two flattened
sides, which meet in a vertical ridge above the neural canal, and look
forward, outward and upward; extending laterally more and more beyond
the side of the centrum, but not reaching so far back as the posterior
articulation of the centrum. Each side of the neural arch at its middle
part behind is produced into a thick obliquely flattened process,
the under portion of which shows the small posterior zygapophysial
facets, which look downward, outward and backward. The lateral outline
of the part of the neural arch above this process is concave; as is
the lateral outline between it and the centrum. Behind, the neural
arch is concave, and looks a little backward. The neural canal is
stirrup-shaped in front, but is higher and sub-ovate behind. The neural
arch of this, as of all the other vertebræ, except a few dorsals, is
inseparably united to the centrum, without a trace of the line of
union. In the middle of the side of the vertebra, and at what may be
presumed to be the union between the neural arch and the centrum, in a
concavity, is the pneumatic foramen. It is round or oval, and varies
in form and size though not in position. In No. 8 it exhibits the
subdivided reticular structure characteristic of the pneumatic foramina
of birds. In No. 10, which has a short centrum, the pneumatic cavities
are reduced to a few small perforations, no larger than would be made
with fine needles.
The centrum is shorter than in cervical vertebræ, commonly convex
(No. 8) on the visceral surface; often with a slight longitudinal
hypapophysial ridge (Nos. 1; 7; 12) rarely flattened (No. 10). Towards
the hinder part the centrum widens, and becomes concave on the visceral
surface, sending off as do the other cervicals, below the transversely
elongated posterior articulation, a pair of short strong apophyses.
The posterior articulation can only by a modification of the idea
be said to conform to the cup-and-ball plan, for though convex from
above downward and convex from side to side, the elongated transverse
measurement would be three times the depth. On the under side an
impressed transverse line divides the articulation from the concave
part of the centrum below.
Cervical Vertebræ.
Pl. 9.
Case. Comp. Tablet. Specimen.
=J= _c_ 2 1-43
Forty-three specimens are mounted to exemplify the variations in size
and characters of cervical vertebræ. These for the most part are
specific characters; and between the axis and the first dorsal vertebra
the variations in an individual were slight. [Those nearest to the
back, as in birds, are widest in front, and have the highest neural
arches.] The associated series show commonly four cervical vertebræ
behind the axis, and in two cases apparently five; never more. So that
as seven appears to be the number of true cervical vertebræ in most
if not all of the German Pterodactyles, it may be presumed that the
Cretaceous Ornithosaurians also had this character in common, with
Mammals, and probably as persistent. In Iguana there are 6, in Monitor
7, and in Crocodile 8.
The centrum is united to the neural arch as in birds, without a trace
of suture; sometimes the neural arch is no wider than the centrum,
sometimes it extends over the centrum on each side. Those forms
with a narrow neural arch have the neural spine high, and its sides
look forward as well as outward. The pneumatic foramen is oblique.
An example is figured by Prof. Owen, in the memoir on Pterodactylus
simus, pl. 2, fig. 4. The forms with a wide neural arch have the neural
spine rising from the middle of the dorsal surface, erect and equally
compressed from side to side. The pneumatic foramen is horizontal. An
example is figured in Prof. Owen's memoir on Pt. simus, pl. 2, fig. 1.
These two forms of cervical vertebræ may be regarded as typifying two
genera.
In both forms many characters occur in common, and as the specimens
illustrative of special modifications will be described hereafter,
the following description has been made to embrace the chief
characteristics of these vertebræ in Cretaceous Ornithosaurians.
The inferior aspect of the centrum is oblong (being narrower than
long), or quadrate; when quadrate the additional lateral expansions are
external to the pneumatic foramina, and are formed by the neural arch
and zygapophyses. The centrum proper is a little wider in front than
behind, and the side outlines are concave. The base of the centrum is
flattened, or more or less hollow, or more or less tumid and regularly
convex; in front there is often a mesial ridge, which never reaches
the posterior articulation, and forms a prominent tubercle at the base
of the anterior articulation. At the posterior end the outline of the
centrum is concave, and mesially the bone has a hollow corresponding
to the tubercle in front of the adjacent vertebra; and the part of
the centrum on each side is prolonged slightly into a strong rounded
or flattened tubercle below the side borders of the posterior
articulation; these posterior processes, in vertebræ in situ, fitted,
on each side of the mesial anterior process of the vertebra behind, on
to concavities more or less marked. Analagous processes are developed
in the cervical vertebræ of many birds.
All the Cretaceous Pterodactyles have the articular surfaces of
the centrum transversely oblong, as have some birds. The posterior
articulation is convex from side to side, and convex from above
downward, and appears to extend a little further on this neural than
on the hæmal surface; in outline it is commonly an elongated oval,
but sometimes attends on the upper surface of the inferior lateral
tubercles. The anterior articulation is transversely elongated, concave
in both directions, and sub-triangular in outline; that is to say, the
superior outline is more or less convex, and from its limits to the
mesial tubercle at the base, the inferior outlines are more or less
concave.
The neural canal is sub-circular or ovate in outline, and quite as
large as the neural canal in vertebræ of Dinornis of similar size.
The neural arch like the centrum has commonly a depressed appearance.
It always has a neural spinous process which is directed upward. In
the depressed type the neural surface of the vertebra is in outline
usually sub-quadrate, but concave at each side, and concave in front
and behind; the four corners are the processes which support the
zygapophysial facets, the surface is divided into two lateral parts by
the strong neural spine. These lateral parts are from front to back
flat, or slightly concave, or slightly convex; and from the neural
spine outward they are always concave. The neural spine is commonly
sharp in front and flattened behind. The neural arch is placed well
forward, so that while a third of the neural canal remains uncovered by
it behind, rarely a sixth would be uncovered in front.
The anterior and posterior zygapophyses are commonly connected by a
more or less rounded ridge, undefined above, but well defined below,
since under its posterior part at about the middle of the side of the
centrum is placed the pneumatic foramen.
The anterior zygapophysial processes are separated from the anterior
articular surface of the centrum by a more or less oblique channel.
Towards the base of this channel in many vertebræ may be seen a small
and short flattened antero-posterior perforation corresponding in
position with the usually large perforation for the vertebral artery.
If the passages are to be regarded as having subserved such a function,
it will not be without interest to remark the small relative size of
the cerebellum in these animals; since the vertebral artery conveys the
blood to that region of the brain.
The anterior zygapophyses are strong processes directed forward and
outward, compressed a little from side to side; they are placed at the
outer sides of the anterior articular face of the centrum, and extend
in front of it.
The zygapophysial facet is commonly oval and looks upward and inward
and forward.
The posterior zygapophyses are short and massive, but otherwise
correspond closely with the anterior zygapophyses, only with all the
parts reversed, and except that necessarily they are relatively to the
neural canal a little higher.
A sharp and well defined angular ridge, commencing at the back of the
zygapophysis, is directed inward, and forward, and upward along the
posterior margin of the neural arch to the top of the neural spine. The
posterior aspect of the neural arch is concave from side to side, and
makes a right angle with the superior lateral aspect.
The part of the centrum exposed behind the neural arch is convex above
from side to side.
The pneumatic foramen between the centrum and the neural arch varies
greatly in size; it is oval and longitudinal.
The largest specimens have the centrum 2-1/2 inches long; in the
smallest the centrum measures 5/8ths of an inch in length.
In the second type of cervical vertebra the side of the centrum makes
a right angle with the base, and is separated from it by a sharp angle
as in struthious birds. The side of the centrum is concave, with a
few small pneumatic perforations; and the side of the centrum, which
is high posteriorly, rounds over the oblique ridge connecting the
zygapophyses, into the oblique lateral face of the neural arch. The
anterior zygapophyses are very large and the posterior zygapophyses
small and placed as high as the top of the neural canal.
Every region of the vertebral column displays pneumatic foramina,
situated as in the vertebræ of birds.
The large proportional size of the neck-vertebræ is common to some
birds, and is conspicuous in many mammals, like the Llama. In most
mammals where the vertebræ have a cup-and-ball articulation, the ball
is in front, as it is in the dorsal vertebræ of the penguin, so that
those vertebræ are not comparable with Pterodactyles, although on the
under side of the centrum they similarly give off a mesial process
below the cup, and a lateral process below the ball on each side. The
neural spine in Pterodactyle is commonly more developed than is the
case with long-necked birds or mammals. Reptiles such as Crocodiles and
Lizards have the neural spines of the neck-vertebræ well developed.
Birds differ from Pterodactyles in the peculiar articulation of their
vertebræ. In both the centrum is often depressed, in both it is concave
from side to side in front, and convex from side to side behind, but
in birds it is also convex from above downward in front, and concave
from above downward behind, while the reverse arrangement obtains in
Pterodactyles. A similar condition to that of the bird is seen in
the neck-vertebræ of the Kangaroo, of Man, and several mammals, only
the vertical curves are less marked. Vertebræ concave in front, and
convex behind, and devoid of cervical ribs, are met with among the
Lizards, but neither Monitor nor Iguana offer any parallel to the form
of the cervical vertebræ of Pterodactyle, which is best matched among
Marsupials and Birds. Birds commonly have more vertebræ in the neck
than have Pterodactyles, which in that respect resemble mammals and
some Lizards.
Dorsal Vertebræ.
Pl. 10.
Case. Comp. Tablet. Specimen.
=J= _c_ 3 1-20
Twenty specimens are mounted to exemplify pectoral and dorsal vertebræ.
Like the cervical vertebræ, they include two types of form, one with
the centrum flat, figured in pl. 2. fig. 20-22 of the memoir on
Pterodactylus Sedgwicki, and regarded by Prof Owen as anterior dorsal;
and the other form with a convex centrum, figured 24-25 of the same
plate of the same memoir, regarded by Prof. Owen as posterior dorsal.
Following the analogy of birds such determination is as well supported
as the similar reference of the two types of cervical vertebræ to
anterior and posterior parts of the neck, but fuller materials compel a
reference of the two types of dorsal vertebræ to two different genera.
Nos. 1, 3, 6, 7, 8, 9, 10, 14, 15, 19 belong to the flat type. Nos.
2, 4, 5, 11, 12, 16, 17, 18 exemplify the convex type.
Dorsal vertebræ are rare fossils; and in the associated sets of bones
never more than four dorsal vertebræ are found, rarely more than one.
No specimen of the type with a convex centrum occurs in the associated
sets.
The dorsal vertebræ with convex centra have all lost their neural
arches except No. 2. The form of the centrum is half a cylinder, as
long, or longer than wide, but sometimes depressed, and wider behind
than in front. The exterior surface is smooth, convex from side to
side, and slightly concave from front to back. The neural surface is
mesially excavated. Both anterior and posterior articular surfaces are
semicircular or sub-ovate, being wide from side to side.
The anterior articulation is cupped, concave from the neural to
the hæmal surface, and concave from side to side. The posterior
articulation is convex from the neural to the hæmal surface, in which
direction, it usually shows striations, and from side to side has a
gentle convexity, sometimes so slight as to be nearly flat.
The neural canal is large, ovate, and as high as is the centrum.
The neural arch is strong, compressed from back to front, and placed
as usual on the anterior part of the centrum. In outline it is
sub-rhomboid with the sides concave. There is a strong process on
each side above the neural canal for a rib, and apparently a neural
spine, but all are broken. The transverse processes for the ribs are
directed outward, and a little forward, flattened in front and behind,
the surfaces being sub-parallel, so that in front the neural arch
is concave from side to side. Behind, the neural spine is directed
between the transverse processes so as to over-hang the exposed part
of the superior surface of the centrum. At the points where the neural
spine bends back from the transverse processes are the posterior
zygapophyses, high above the neural canal, and parted from each other
by an interspace as wide as the canal is high. They look downward,
outward, and backward. The lateral surface below the transverse process
is narrow, flattened, bends at a right angle with the posterior
surface, rounds into the anterior surface, is a continuous curve with
the side of the centrum, and is concave from below upward. The superior
surfaces of the neural arch have the sides sub-parallel, they are
each concave from side to side; and these surfaces are excavated for
pneumatic foramina.
Dorsal vertebræ of the type with the centrum flattened closely resemble
cervical vertebræ with the centrum flattened, differing chiefly in the
less length of the centrum. Occasionally (as in No. 3) the neural arch
comes away from the body of the vertebra.
The centrum is very depressed, sub-quadrate, and wider than long;
the base is flat, or slightly concave, with occasionally a slight
longitudinal mesial ridge; the lateral outlines are concave, so that
the bone is pinched in from side to side. The neural surface of the
centrum is flat and parallel with the base, and, as usual, wider behind
than in front, but the centrum is not there so high. The surfaces for
the neural arch are flat, and extend nearly to the base of the centrum
in front, so that they look upward, outward and a little forward.
The articular ends are remarkable for their depressed oblong character,
still preserving the anterior concavity with a small mesial process
below, as in cervical vertebræ, and similar but smaller processes
at the inferior outer angles of the posterior sub-semicylindrical
convexity. The middle third of the anterior cup is made by the
trapezoidal anterior end of the centrum; sometimes the sutures between
it and the neural arch are well marked.
The neural arch is large, commonly with a sub-circular neural canal.
The neural spine is high, compressed so as to have the lateral surfaces
sub-parallel and rounding into each other superiorly; and it has a
less antero-posterior extent than the centrum. At its base behind
it widens rapidly, and forms massive quadrate processes, extending
outward and backward, which on the outside each have a flattened ovate
zygapophysial facet, which also looks downward. Above the facet and
separated from it by a groove is a tubercle. Between the zygapophyses
behind the bone is concave from side to side; the facets are placed
above the neural canal.
The posterior zygapophyses are placed considerably higher than the
anterior zygapophyses, and the part of the neural arch between is
rather constricted from front to back. The neural arch steadily widens
in front down to the base of the anterior zygapophysial processes in
such way that the more or less flattened lateral surface looks outward
and is gently concave from above downward. A ridge commencing at the
tubercle over the posterior zygapophysial facet descends in a curve
forward and downward, to form the posterior border of the anterior
zygapophysial process. This is separated by a groove from the anterior
articular surface, and anterior part of the base of the centrum, and
has the aspect of a compressed part of the neural arch, extending
obliquely downward, and forward, over and beyond the articular surface
of the centrum. The anterior zygapophysial facets are oblong, narrow
from side to side, and long from front to back; they are directed
forward and a little outward, and are flattened, make nearly a right
angle behind with the front of the neural arch, and look upward and
inward. They are sometimes placed as high as the top of the neural
canal, but are commonly lower. Around the neural canal the bone is
conically impressed.
Minute pneumatic foramina are in the usual position, between the
centrum and the neural arch; and sometimes others behind the anterior
zygapophysial process.
The largest specimen known has the centrum nearly an inch and a half
long.
The dorsal vertebræ in Cambridge specimens would appear to make a
nearer approximation in number to birds than to Mammals or Lizards or
Crocodiles, though Chelonians have few vertebræ in the back. Among
Reptiles the form of the vertebra makes some approach to that of the
Monitor, Chameleon and Scink. In most Mammals the dorsal vertebræ have
the centrum convex, though in the lumbar region its visceral surface
often becomes flattened. But though very unlike there is a nearer
resemblance to the lower dorsal vertebræ of a Struthious bird.
Sacrum.
Pl. 10.
Case. Comp. Tablet. Specimen.
=J= _c_ 4 1-7
Seven specimens are mounted to exemplify the ordinary structures of the
Ornithosaurian sacrum.
Nos. 1 and 2 have the centrum convex, exactly as in the dorsal vertebræ
of the convex type. Nos. 3-7 have the centrum flattened, following in
general features the plan of the dorsal vertebræ with flat centra.
No. 1 is a vertebra from a sacrum, where perfect anchylosis had not
been induced; it has the neural arch well preserved, and shows the
sharp suture which united it to the preceding vertebra.
No. 2 shows two entire vertebræ and part of a third, which have lost
the neural arches but have the centra perfectly anchylosed together.
The middle vertebra measures 5/8 of an inch in length, and at the
suture from side to side measures more. The surface is smooth,
regularly convex from side to side, and gently concave from back
to front. The last vertebra shows the articular vertebral surface;
it is convex in both directions, and oblique, so that a large part
looks upward. The anterior of the three vertebræ is pinched in at the
lower part of the sides of the centrum. No. 1 shows that the neural
surface of the centrum is deeply excavated, making the neural canal
an elongated upright oval. Above the centrum, which forms only the
middle third of the articular surface, the neural arch expands on each
side into a wedge-shaped transverse process, the lower surfaces are
flattened, and continuous with the centrum, while the upper surfaces
are flat and horizontal as in birds and Dinosaurs, and form the
platform from which arises the massive neural spine.