vertebral column. The types in which it attains any size as an expanded
shield are Cetaceans and the Manatee, but in these groups it has no
keel and is not connected with the other bones of the pectoral girdle.
The proximal portion of the sternum of the Mole is elongated and
bird-like, with the shield narrower than in the typical gallinaceous
birds, and with the keel similarly developed. It is connected with the
humerus by small sub-quadrate bones named clavicles placed at the sides
of the proximal end. The sternum in Bats usually consists of a proximal
and a distal part. It is narrow except at the proximal-termination
where it widens like the letter T or Y; and to the sides of the lateral
prolongations are attached the long, slender, curved bones named
clavicles, and a pair of ribs. This sternum develops a bird-like keel.
Both Mole and Bat are regarded as differing from Pterodactyles in the
bone giving attachment to the clavicles instead of to the coracoids.
The proximal part of the sternum in both the living animals, gives
attachment to but one pair of sternal ribs. The Pterodactyle sternum
otherwise differs from the Bats in having the articulations for the
coracoids close together, of a peculiar concavo-convex character, with
a massive portion or keel prolonged forward in front of the coracoid
articulations. The Bat cannot be said to resemble the Pterodactyle
closely. The sternum of the Mole differs from that of the Pterodactyle
in having a less developed shield, and in having a more developed keel
which is not prolonged in front of the coracoid articulations. These
examples demonstrate that resemblance in conformation is functional,
and no proof of affinity.
Pterodactyles make some approach in the proportions of their sternum
to Struthious birds. But the Struthionidæ have the bone thick, do
not develop a keel, nor, have they an inter-coracoid process while
the coracoid articulations are singularly long and narrow instead
of being ovate. With other birds the Pterodactyle sternum agrees in
giving attachment to the coracoid bones by synovial articulations, in
the bone being shield-shaped, and supporting a more or less developed
keel. The keel is chiefly developed at the proximal end, as in the
Albatross, which has the bone broad; and it is prolonged in front of
the coracoids exactly as in _Mergus merganser_, which sternum if a
little broader in the shield and thicker in the keel would very nearly
reproduce the sternum of the Pterodactyle, even to the "post-coracoid
lateral emargination" of Cambridge specimens. Among reptiles the only
form which suggests comparison is the Chameleon, in which however the
sternum consists of an anterior and a posterior part as in the Bats,
the back part narrow, and the front part a long lozenge shape, with
a keel made by inclination of the sides of the bone to each other as
in the Dodo, but the keel such as it is, is at the back part of the
bone, and there is no prolongation in front of the coracoids as in
Pterodactyle. The coracoids are broad, and are applied to the two
anterior sides of the lozenge. The Crocodile has a narrow flat sternum
which is prolonged anteriorly between the coracoids.
The resemblance is greater with mammals than with reptiles. From birds
the Pterodactyle sternum makes no essential difference, and in the
Merganser finds a close ally.
CORACOID.
Pl. 2, fig. 1-6.
Case. Comp. Tablet. Specimen.
=J= _a_ 2 1-23
Commonly the coracoid in the Cambridge Pterodactyles is anchylosed to
the scapula: occasionally the bones are separate, though the separation
has hitherto only been observed in the largest species. In 1851
Professor Owen, when figuring the anchylosed ends of the scapula and
coracoid in Pterodactylus giganteus (Bowerbank), observed that in no
part of the skeleton does the Pterodactyle more nearly resemble a bird
than in the scapular arch; a view again urged emphatically in 1859 when
similar fragments were described from the Cambridge Greensand. Since
then perfect examples of the coracoid have occurred, which show the
characters given in the following description.
The bone is long, with sub-parallel sides, sub-triangnlar in section,
with the proximal end expanded exteriorly and posteriorly, resembling
in form the coracoid of a bird. The front surface looks forward and
outward; it is flattened, is a little convex transversely, and a
little convex in length; it is rugose with muscular attachments, which
terminate in a tubercle on the uppermost fourth of the front, usually
near to the inner side. The middle third of the slightly concave
inside margin of the front aspect, is sharply angular; the parts above
and below it have the angularity rounded off. The outside margin, a
little more concave than the inside margin, is sharply angular in its
distal third, in which the front gradually widens to near the sternal
articulation, when it contracts--the whole sternal termination of
the bone being directed a little inward towards the manubrium of the
sternum. The inside, which faces the opposite coracoid, is convex
transversely in the lower half or two-thirds; its distal termination is
carried inward. The expanded proximal end of the inside is flattened,
or channelled, by the developement inwardly, at the proximal end
of the ridge formed with the front side, of a long strong process
homologous with that on the inner side of the coracoid in birds. The
channel so formed rounds on to the proximal surface of the bone, and
extends backward to the limit of the scapula; over it the second
pectoral muscle may be presumed to have worked[N]. The third side of
the bone is much more concave in length than either of the others;
it looks backward, outward, and downward, the proximal end being
turned outward and downward more than the distal end; it is a little
concave transversely at the expanded proximal end. Near the distal
end there are sometimes visible a few faint marks of the insertion of
muscular fibres, but they are much less distinct than those made by the
coraco-brachialis muscle in the corresponding region of the coracoid
in birds. Throughout its length it rounds into the inner side, and the
upper third rounds convexly into the front. On the most posterior part
of this aspect of the proximal end is a groove terminating in a long
pneumatic foramen, partly in the coracoid, partly in the scapula.
[Footnote N: The homologous process is more developed in Pterodactylus
giganteus. See f. 7. pl. XXXI. Owen, Cret. Rept.]
The muscular attachments on the front aspect of the coracoid appear to
be two; one large and long inserted into the inner half of the middle
third of the bone, terminating at the proximal end in a tubercle. No
specimen shows the distal end of the insertion. This may indicate a
subdivision of the first pectoral muscle. The other insertion, if it be
distinct, is long and much narrower and at the distal end of the bone.
This, according to the analogy of birds, should be the third pectoral
muscle; if the insertion should be but part of that to which it is
distally adjacent, then the third pectoral muscle must have had an
enormous developement unparalleled in birds.
The distal end of the bone terminates in a synovial articulation
concave transversely, convex from front to back, in form transversely
ovate: the narrow side of the articulation, like the thin edge of the
coracoid, being exterior. The articulation is about three fourths of
the transverse diameter of the distal end; it is at right angles with
the long axis of the bone, and looks downward and a little backward.
The proximal end, massively enlarged outward and backward, presents on
the proximal surface three well defined regions. The largest of these
is an irregular flattened surface half ovate in form, inclined to the
axis of the bone at about 45°, looking backward, and upward also,
when the bone is held vertically; the mesial hindermost half of the
radius of this area is occupied by a pneumatic cavity: to this surface
is applied the scapula. The next largest surface is rectangular and
oblong, looking upward, outward, and a little forward. The transverse
aspect which looks outward being nearly half as long again as the
antero-posterior aspect which looks forward; in the latter direction
the area is slightly concave, in the former direction it is slightly
convex; its posterior boundary is parallel with the front of the bone:
this area forms the anterior moiety of the glenoid cavity, to which the
proximal end of the humerus is applied.
The remaining surface of the proximal end is sub-quadrate, adjoins the
two other surfaces as well as the front and the inside of the shaft, it
is conically concave.
The entire bone when applied to the sternum looked outward, backward
and upward.
Professor Owen remarked (1859) that the "coracoid is shorter and
straighter in birds than in Pterodactyles, but is commonly broader, and
with a longer and stronger anterior process."
The points in which the Pterodactyle coracoid resembles that of
birds (e. g. Gallinaceæ) are the long slender triangular shaft; the
concavo-convex articulation to the sternum; the convexity of the distal
end in front, and its concavity behind; the posterior aspect of its
scapular surface, and the pneumatic foramen.
The points in which it is distinct from birds are that the bone is
not produced proximally beyond the glenoid cavity for the humerus,
which, instead of being lateral as in birds, and looking outward,
in Pterodactyles forms the proximal-termination of the bone. The
sternal articulation is proportionally much shorter transversely in
Pterodactyles, terminating in a convex margin which rounds up into the
thin outer margin, as in the immature coracoid of the common Cock.
It is bow-shaped in front instead of being straight, and is commonly
longer than in birds. The usual ossified connection with the scapula
is not entirely unparalleled in birds, the whole pectoral girdle being
sometimes anchylosed into a bony mass as in the frigate bird.
In the monotremata, the only mammals in which the coracoids are
separate bones, they rather recall those of Ichthyosaurus than those of
any other animals, and have no connection with the sternum. The bone
which represents it functionally in placental mammals is the clavicle.
In no reptile is there any structure resembling the Ornithosaurian
coracoid. The nearest approximation is made by the Crocodile, in which
as in the Chameleon the pectoral girdle is formed as in pterodactyles
and struthious birds by scapula, coracoid and sternum. But in the
Crocodile the coracoid is compressed, and expanded from side to side
both proximally and distally. Distally it has no synovial articulation
with the sternum; and proximally a wide process of the bone extends
beyond the articulation for the humerus as in birds, only the scapula
unites with the prolonged part, and the glenoid cavity looks forward
and inward.
The coracoid is essentially avian in its affinities, though with
peculiar characters of its own. In the German genera it closely
resembles specimens from the Cambridge Greensand.
23 specimens are exhibited. Nos. 4, 10, 12, are the middle parts of
shafts of left coracoids. Nos. 3-12, 22, are the middle parts of shafts
of right coracoids. Nos. 2, 5, 14, are proximal ends of left coracoids.
Nos. 1, 6, 8, 9, 23, are proximal ends of right coracoids. Nos. 15,
16, 17, 18, 19, 20, 21, are distal ends of left coracoids. No. 13 is a
nearly perfect left coracoid, and No. 7 is the glenoid cavity for the
humerus formed by a right coracoid with the anchylosed scapula.
SCAPULA.
Pl. 1, figs. 2-12.
Case. Comp. Tablet. Specimen.
=J= _a_ 3 1-17
4 1- 6
5 1- 4
Professor Owen described the scapula of Pterodactylus giganteus in
1851, and added further particulars regarding the Species from the
Cambridge Greensand, in 1859; but, as with the coracoid, only the
humeral end has hitherto been figured. The only example sufficiently
perfect to give the length and proportions of the bone is preserved in
the collection of Mr Reed, of York. This left scapula is a stout strong
bone, short in proportion to its strength, of flattened ovate form in
section, expanding at the humeral end into an irregular sub-rhomboid
mass. It is smaller in the middle, contracting both from side to side
and from back to front till the back to front measurement is 7/16 of
an inch, and the side to side measurement is 11/16 of an inch, and
it expands a little at the free end, which terminates in a smooth
heart-shaped surface, convex in the long diameter, which measures 7/8
of an inch, and flat in the short one, which measures nearly 5/8 of
an inch; it is at right angles with the inside of the bone. The sharp
superior lateral outline is concave, but less so than the inferior
lateral outline; into that inferior aspect of the bone the sides are
more fully rounded. The flattened inner surface applied to the ribs is
concave in the length of the bone, which measures 3-1/2 inches; the
posterior half of which is convex transversely, the anterior humeral
half is concave transversely so as to be cup-shaped, and measures in
extreme width 1-11/16 inch; the outline of the transversely convex
outer side in length is nearly straight, but the exterior part and
glenoid cavity of the proximal end is broken away, and there only
remains a small median proximal sur&ce broken at both ends, a little
concave in length, measuring 5/8 of an inch, and convex in breadth
measuring 1/4 of an inch.
As there is no specimen in the Woodwardian Museum showing clearly the
connection of the proximal with the distal end, the specimens are
arranged on separate tablets.
Humeral End of Scapula.
The humeral end of the scapula exhibits in the different species much
diversity of form, spreading laterally from the shaft, and terminating
in an elongated articular surface truncating the bone nearly at
right angles. On its inferior border it throws out a large convex
tuberosity, separated from the humeral articular surface by a deep
emargination. From the tuberosity usually arises a crescentic row of
muscular insertions, which is continued inward and forward over the
most compressed part of the scapula towards the middle of the humeral
articulation. From the superior margin, interior to the coracoid,
arises a prominent ridge, the spine of the scapula, which is directed
diagonally backward and downward, terminating in the middle of the
outer surface, where it is bordered on the anterior aspect by a long
narrow muscular attachment. Between this spine and the elevated margin
of the glenoid cavity the bone is much compressed and concave.
On the inside surface of the bone there appear to be small muscular
attachments in front of and behind the great tuberosity. The area
between the spine and the inner surface is sometimes flattened,
sometimes gently convex.
With well-marked distinctive characters in the inferior tuberosity,
the pre-tuberous emargination and the thick rounded form of the bone,
the Pterodactyle scapula is intermediate in character between that
of a mole, a bird, and the crocodile; wanting the sabre shape of the
bird's scapula, it also wants the wide expanded form of the scapula of
the Crocodile, but resembles the latter in the direction and degree of
developement of the spine. This modification is probably due to the
outward direction and clavicular function of the coracoid, as well as
to the raptorial habit of the organism.
In no living Reptile is there a scapula to be compared with that
of the Pterodactyle, for besides the free end being expanded, in
the crocodile, it is also thin and squamous and the bone makes a
continuous curve with the coracoid as in struthious birds, and not a
sharp angle as in Pterodactyles. The "spine" in crocodiles is on the
anterior border of the bone and directed upward and backward, while in
Pterodactyles it is on the posterior border and directed upward and
forward. In the Chameleon the scapula is more elongated and narrow,
narrower in proportion to its length than in Pterodactyle, but becomes
rapidly wide at its union with the coracoid. It is curved in length so
as to fit on to convex ribs. A scapula presenting some resemblance to
Pterodactyle is found in certain Liassic Ichthyosaurs.
Among mammals a straight elongated narrow scapula is rare. The mole
however has a scapula of this kind somewhat cylindrical in its proximal
half and not much expanded at the free end, on which there is a
small spine. The anterior emargination above the glenoid cavity in
Pterodactyle is entirely mammalian, as is the anterior tuberosity above
the emargination, for it entirely corresponds with what in ruminants,
pachyderms and many mammals would be named the coracoid process. If
that process is accurately determined it is difficult to say what this
is.
In birds there is often a prolonged process on the inner side of the
coracoid, which however extends interior to other parts of the scapula,
and to this the furculum is attached. Such traces of a spine as are to
be detected in the swan conform to the Pterodactyle.
No bird has the scapula cylindrical, even struthious birds only making
an approximation to such a condition; and no birds have the scapula so
straight. The bone is more avian and mammalian than reptilian; and
more avian than mammalian but with strong distinctive characters of its
own.
17 specimens of the humeral ends of scapulæ are exhibited. Nos. 1, 4,
6, 7, 8, 9, 11, 13, 14, 15, 17 are left scapulæ. Nos. 2, 3, 5, 10, 12,
16 are right scapulæ.
The tablet of the distal ends of scapulæ comprises 6 specimens.
Fore-Limb.
HUMERUS.
Pl. 4.
Case. Comp. Tablet. Specimen.
=J= _a_ 6 1-46
7 1- 3
8 1
There are among the fossils of the Cambridge Greensand at least two
well-marked _types_ of Pterodactyle humerus, readily recognised by the
forms of the proximal and of the distal ends, and by the positions of
the pneumatic foramina. In the group having the ulnar ridge developed
the pneumatic foramen is on the posterior aspect of the bone[O] under
the ulnar ridge, as in birds; but in some of the small Pterodactyles
the foramen is on the anterior surface, and on its radial side. This
latter kind of humerus has the distal end more or less divided into
three convex surfaces, while the radial crest is enormously developed
and terminates in a smooth oblong flattened surface nearly as large
as the proximal articular surface, and looking anteriorly. The distal
articular surfaces are not as in birds parallel to that of the proximal
end, though they agree with those of birds in being at right angles
to the radial crest; this ridge in Pterodactyles being directed much
further outward and backward than in birds.
[Footnote O: Professor Owen states (p. 16, 3d Supt.) that the foramen
is palmar. Fig. 15. T. III. 2d Supt. shows it to be anconal.]
The largest forms of Pterodactyle all have the distal articular surface
flatter, and the proximal articulation less bent back so as to look
more upwards. No specimen of this kind of humerus has occurred with the
radial crest preserved; but it is apparently carried farther down the
shaft and not so far forward as in the other group. This latter kind
of bone is shown by Prof. Owen in T. III. figs. 1, 2, 3rd Sup. Cret.
Reptiles; the former kind has been illustrated in figure 5 of the same
plate.
Some of the most gigantic Pterodactyles appear to have had the
limb-bones as solid as those of crocodiles, and unpermeated by air;
and there is no evidence that the high Avian characteristics of most
of these Greensand fossils also pertained to all the previously known
types from the lower secondary rocks.
The osteological series comprises 46 specimens. No. 30 is a nearly
perfect right humerus. Nos. 1, 2, 5, 6, 7, 8, 9, 11, 18, 22, 23, 25, 39
are examples of the proximal ends of left humeri. Nos. 3, 4, 10, 12,
13, 14, 15, 16, 17, 19, 24, 26, 27, 28, 38, 40, 41 are examples of the
proximal ends of right humeri. Nos. 20, 21, 32, 33, 34, 35, 37, 42, 44,
45, are examples of the distal ends of left humeri. Nos. 29, 31, 36, 43
and 46 are distal ends of right humeri.
No. 30 shows the entire length of the humerus to be 2-1/2 inches. It
has a nearly circular shaft with a diameter of a little more than a
quarter of an inch, being more slender than the corresponding bone
of Pt. suevicus, which has the same length. The _proximal_ articular
surface is crescentic, the anterior concavity corresponding with
the concave anterior aspect of the proximal end, while the convex
border corresponds to the convex posterior side of the bone, which
it overhangs: it is worn, but appears to measure half an inch from
the radial to the ulnar side. The ulnar ridge (which is worn) has
not extended more than a quarter of an inch beyond the articular
surface. The thin bird-like radial crest, arising rather more distally
than the ulnar ridge, is flat on its posterior surface, and extends
anteriorly for a distance nearly half as far again as the length of
the proximal articular surface of the humerus. On the proximal third
of the posterior face are two contiguous long narrow oblique muscular
insertions. The proximal ends Nos. 22, 23, 24, 25 are examples of this
kind of bone, having the pneumatic foramen radially situated on the
anterior aspect near to the articular surface, as may be seen in No.
24. No. 25 shows the termination of the radial crest in an oblique
oblong smooth surface, slightly convex in length and breadth, directed
distally towards the ulnar side.
No. 6, 7, 13, 27, are examples of another kind of proximal end,
where the pneumatic foramen is an oval hole on the ulnar side of the
posterior sur&ce. The radial crest arises more distally, and the ulnar
ridge more proximally, than in the small species, like No. 30.
Nos. 4, 11, 14, 16 are examples of other species with the foramen
placed as in the last group, only less near to the proximal end, while
it enters obliquely, being directed distally from the broad concave
area proximal to it. The largest proximal ends known, such as No. 2,
which though very imperfect measures 2-3/4 inches over what remains of
the articular surface, appear to conform to this latter type.
_Distally_ the humerus No. 30 enlarges, widening rapidly on the radial
side, which is bordered near the distal end by a sharp ridge showing
a muscular attachment, while the ulnar side is rounded and rather
inflated. The articular surface looks downward and in the direction
of the radial process. There is a mesial concavity on the radial side
which is bordered on the right and on the left by a prominent rounded
condyle, and behind by a condyloid convexity. On that side which in
conformity with the nomenclature applied to birds' bones, has here been
named the ulnar side, the ulnar and mesial condyles are impressed with
a flattened slightly concave sub-rhomboid area, which looks downward,
backward, and towards the ulnar side. These characters are not well
seen in No. 30, but may be effectively studied in their specific
variations in Nos. 36, 37, 42, 43, 44, 45, and 46.
Nos. 20, 21, 29, 31, 32, 33, 34, 35, are examples of the distal ends of
humeri of a different type. They are mostly larger than the preceding
group, and correspond in characters with the large proximal ends, but
appear to be separable into two groups, namely those with a pneumatic
foramen on the anterior radial side near to the articular surface,
and those where no pneumatic foramen is seen. Unlike the previously
considered type, the ulnar side is sometimes more inflated than the
radial side.
The mesial condyle in this group appears in every case to be an
epiphysis, which is wanting. The radial condyle becomes a large
flattened slightly convex surface looking downwards, which in some of
the species, as Nos. 21 and 32 (in other respects remarkable species),
shows an approach to a trochlear character on its anterior side. In
Nos. 33, 34 and 35 the mesial anterior concavity becomes flattened and
abuts at an angle against the flattened radial condyle. No. 20 shows
the rhomboid impression on the ulnar side to be more concave and more
ovate. The ulnar condyle remains a smaller but prominent tubercle
directed distally. Nos. 21, 22 and 34 show a ridge developed on the
ulnar side of the shaft like that on the radial side in the other
group, while the radial ridge is not so near to the articular surface.
The largest and smallest distal ends of humeri known, both show the
characters here enumerated. The great distal end of a left humerus,
figured by Prof. Owen, Pl. IV. f. 1, 2, 3 of the 1st Supplement to the
Cretaceous Pterosauria, is of this kind, and though imperfect measures
more than three inches over what remains of the articular surface. In
the small humerus, No. 30, the width over the distal articular surface
is 5/8ths of an inch. If it is assumed that the large bone was no more
than 5 times the length of the small one, the entire length of the
humerus would have been about twelve inches. The smallest humerus, No.
29, measures over the shaft rather more than one eighth of an inch.