“superoccipital foramen”) as exemplifying the affinity of the Dodo, the
more essential characters of the skull relate to its true Columbine
character, while the deviations from that part of the skeleton of
volant Doves are explicable in the adaptive developments needed for the
wielding of long, powerful, massive mandibles, serving most probably
to enable the bird to subsist on some proportion of animal diet, in
addition to such vegetable food as it might gain from the ground. Such
indiscriminate feeding doubtless rendered its flesh less palatable than
that of the winged Pigeons of the Mauritius to the Dutch navigators of
the sixteenth and seventeenth centuries.
But the affinities of _Didus_ will be more fully and decisively brought
out in the comparison of the, in this respect, more instructive and
light-giving parts of the skeleton.
§ 3. _Comparison of the Skeleton._
The dorsal region of the vertebral column shows, in some birds, a
confluence of certain vertebræ: I have observed four to be so welded
together by both centrums and neural spines in _Phœnicopterus_, viz.
the second to the fifth dorsal inclusive, leaving the sixth free, which
articulates with the first costigerous sacral vertebra. In _Platalea_
three dorsals coalesce in advance of the antepenultimate free vertebra.
In the smaller diurnal birds of prey five dorsal vertebræ are usually
confluent, leaving one free vertebra for the lateral movements of the
trunk between such dorsal “sacrum” and the pelvic one. In Vultures,
Plovers, Bustards, Cranes, _Psophia_, _Cariama_, _Palamedea_, Auks,
Penguins, and in all flightless land-birds save the Dodo, no such
anchylosis takes place. The _Columbidæ_ are the species in which the
dorsal vertebræ, homologous and the same in number with those of
_Didus_, undergo the process of confluence into one mass of bone:
they are the three which immediately precede the last (moveable)
dorsal vertebra; and of these the two anterior develope, in _Goura_
and _Didunculus_, hypapophyses closely corresponding in shape and
proportion with those in the Dodo.
The chief difference which _Didus_ offers in the present region of the
vertebral column from that of _Columbidæ_ is in the greater number
of the vertebræ or segments which are typically completed by bony
hæmapophyses articulating with pleurapophyses and directly with their
mass of coalesced and expanded hæmal spines constituting the sternum.
Of these typical thoracic segments there were five in _Didus_ (Pl.
III.); _Didunculus_ (ib.) shows four; _Goura_ three. In both existing
genera these segments are succeeded by a single one, anchylosed to
the fore part of the sacrum, but with the pleurapophysis long and
moveable, with its hæmapophysis terminating in a point before reaching
the sternum, and extensively connected with the antecedent hæmapophysis
or sternal rib: in both genera two dorsal vertebræ in advance of the
typically complete one have moveable pleurapophyses terminating freely
in a point, with no hæmapophyses other than the costal processes of
the sternum may represent. In _Goura_, which has six pairs of moveable
or thoracic ribs, the second pair belong to the first of the three
anchylosed dorsal vertebræ: in _Didunculus_, which has seven pairs of
thoracic ribs, the second pair belongs to the free dorsal immediately
in advance of the anchylosed mass. Supposing _Didus_ to have had one
pair of ribs behind, and two pairs in front of those that directly
articulate with the sternum, as the vertebra Pl. V. fig. 7 indicates,
it would have had eight pairs of thoracic ribs; and I think this excess
of one pair beyond the formula in _Didunculus_ to be very probable in
the large-bodied, small-winged, extinct Ground-dove.
As far as the series of Dodo’s neck-vertebræ under my observation
exhibit such characters, the proportion of those with neural spines,
or with hypapophyses, or both, is the same as in the _Columbidæ_. In
this family, as in most birds, the greater part of the series want
both processes. The cervical parapophyses, descending to form the
sides of the carotid canal, do not meet, coalesce, and circumscribe
it in any cervical vertebra of _Goura_ or _Didunculus_; and not any
of the vertebræ of _Didus_, which I have yet received, shows such
circumscription of the hæmal canal. The majority of the cervicals in
_Didus_ (those, viz., that lack both neural spines and hypapophyses)
are broader and more massive in proportion to their length than in
the winged Doves. The third cervical in _Didus_ has both the above
processes, as in _Columbidæ_: the characters of the axis vertebra
in the same family are closely repeated in that of the Dodo. In the
Raptores the axis vertebra is shorter in proportion to its length,
and a greater proportion of the cervical vertebræ at both ends of the
series have both neural spines and hypapophyses.
The ribs of the Dodo are as broad, in proportion to their length, as in
Doves, but are relatively longer in proportion to the dorsal region,
encompassing a more capacious thoracic-abdominal cavity. The ribs
of the Vulture are more expanded than in _Didus_, especially where
they afford the extensive attachment to the epipleurals. But I shall
not dwell further on the comparative characters of this part of the
skeleton, as more decisive ones of the affinity of _Didus_ are afforded
by other parts.
In comparing the sternum of the Dodo with that of Doves of flight,
the first well-marked difference is in the adaptive development of
the keel in the last (Pl. III. fig. 2, _Didunculus_), and in the
provision for the concomitantly broader coracoids, the grooves for
which meet and run into each other across the fore part of the bone in
existing _Columbidæ_ (Pl. XII. fig. 2, _b_); consequently the inner
or upper wall of the confluent grooves forms a median prominence (ib.
_e_) at the front margin of the sternum, contrasting with the wide
notch at that part of the bone in the Dodo (Pl. IV. fig. 4). The next
difference, as compared with _Goura_ and most Pigeons, is the absence
of the entolateral processes (Pl. XII. fig. 3, _i_) in the Dodo’s
sternum: but _Didunculus_ singularly exemplifies its nearer affinity
to _Didus_ by a like absence of those processes; only the sternal
margins behind the ectolateral processes (ib. fig. 1, _h_), instead of
converging with a slight convexity to an obtuse apex, as in Pl. VI.,
describe a concavity, through an expansion of the posterior truncate
end of the breast-bone. The sternum of _Didunculus_ may be said to
show one pair of posterior notches (Pl. XII. fig. 1, _f_), that of
other Pigeons two pairs (ib. fig. 3, _f_ _f′_); but the sternum of
_Didus_, which is relatively broader, shows no other trace of the
anterior notch (Pl. VI. _f_) than is afforded by the rounded angle at
which the ectolateral process (_h_) rises from the bone. Although the
costal margin is relatively shorter in Doves of flight than in the
Dodo, again an intermediate condition is manifested by _Didunculus_
as compared with _Goura_, in which latter Dove there are articular
surfaces for three sternal ribs (Pl. XII. fig. 3, _o_ 1, 2, 3),
whilst in _Didunculus_ there are four (ib. fig. 1, _c_). _Didunculus_
also exhibits, more strongly than _Goura_, the obtuse ridges (ib.
fig. 2, _r_) converging like buttresses from the outer wall of the
coracoid groove to the fore part of the keel, where they subside. In
_Didunculus_ there is a pneumatic foramen exterior to the coracoid
groove, corresponding with _p_, fig. 4, Pl. IV., which I do not find
in the sternum of _Goura_; but in the Crown-pigeons the pneumatic
foramina along the middle line of the upper surface of the sternum are
conspicuous; they are confined to the fore part of that surface in
_Didunculus_ (Pl. XII. fig. 1).
In the direction of the ectolateral processes _Goura_ (ib. fig. 3, _h_)
is intermediate between _Didunculus_ and _Didus_. The pectoral ridge
on the outer surface of the sternum, continued backward from the outer
end of the coracoid groove, is adaptively better marked in Pigeons
of flight than in the Dodo; and the pair of ridges are more nearly
parallel in their backward course, not so convergent as in _Didus_.
In _Goura_ the subcostal ridge is better marked than in _Didunculus_.
In no Dove of flight is the body of the sternum so broad and hollow
as in _Didus_ (Pl. XI. fig. 4); in this respect the Vulture more
nearly resembles the Dodo, as it does also in the more convex anterior
contour of the keel: but the vulturine sternum does not lose breadth
as it extends backward; it is a square-shaped shield in birds of prey,
shorter in proportion to its breadth, with a greater extent of costal
process and margin, and with the ectolateral processes, when they
exist, extending backward as far as the hinder border of the bone. In
the thorough quest of resemblances to the Dodo’s sternum which I have
made through the class of Birds, I came upon an unexpected superficial
likeness to it in the sternum of a Night-jar (_Podargus humeralis_).
The ectolateral processes (Pl. XII. fig. 4, _h_) rise behind the
moderately extended costal borders, _c_; and beyond them the body of
the sternum converges to an obtuse end, with a contour similar to
that in _Didus_. Moreover the coracoid grooves are divided from each
other by a free concave border, less deep and extensive, indeed, than
in _Didus_, but as free from any trace of episternal projection. The
ectolateral processes, however, are extended backward to beyond the
sternal body; and this part usually shows a pair of small entolateral
notches, _f′_, of which one was present on one side in the specimen
figured.
Through the reduction of the coracoids in all flightless birds, there
is an interval between their sternal articulations: this is long
and concave in the Dodo, but is longest and most deeply concave in
_Apteryx_; it is long but almost straight in _Rhea_; in _Casuarius_ and
_Dromaius_ it is narrow but deeply notched; in _Struthio_ it developes
a short episternal process. In no Grallatorial sternum with both ecto-
and ento-lateral processes (as e.g. _Otis_, _Œdicnemus_, _Charadrius_)
do the former project, as in _Didus_ and the Rasores, immediately
behind the costal margin, but they are continued, parallel with the
keel, from the outer and posterior angle of the sternum, distant from
the costal margin. In old Plovers the entolateral process joins the
contiguous angle of the sternal body, and converts the inner notch into
a foramen.
In the breast-bone of the Dodo we plainly discern the Columbine
modification of the Gallinaceous type, simplified in the minor
development of those parts relating adaptively to the power of flight,
and expanded and excavated for the support of the larger gizzard with
its heavier grindstones[34].
In comparing the pelvis of _Didunculus_ and _Goura_ (Pl. XII. fig.
5) with that of _Didus_ (Pl. VII. fig. 1), the correspondences
are:—in the general shape, proportions and disposition of the ilia;
in the articulation therewith of the last pair of moveable ribs,
and of the short straight confluent pleurapophyses of the three
succeeding sacral vertebræ; then follow, as in _Didus_, three vertebræ
without pleurapophyses, these reappearing in the next two with their
extremities converging to abut against a prominence of the inner
surface of the ilium in the same relative position. The difference
here is in the two equal and more slender rib-buttresses, in place
of the single stronger one, which is the more common structure in
_Didus_; but in _Goura_ I have noted an instance in which it agreed
with the _Didunculus_ on the left side, and with _Didus_ on the right,
in the last-specified character. In the Crown-pigeons, also, there is
an indication of the transverse ridge marking off the under part of
the centrum of the first sacral from the rest, and those that follow
are less expanded than in the Dodlets; moreover in _Didunculus_ they
show a median canal instead of a ridge, while the ridge is feebly
indicated here and there and there is no canal in _Goura_. In neither
_Didunculus_ nor _Goura_ do the sacral centrums behind the last
rib-abutments diminish in breadth so suddenly as in _Didus_: in both
the winged Pigeons the hinder part of the pelvic cavity is relatively
deeper and narrower than in _Didus_; in both, also, the upper and
anterior concave tracks of the ilia are deeper; and in _Didunculus_
the mesial borders do not attain the neural crest, but leave a pair of
open longitudinal canals at that part of the pelvis; in _Goura_ those
margins reach the neural crest, but do not overtop it at any part.
In _Goura_ the acetabula are more in advance of a median position
than in _Didunculus_, _Columba magnifica_, or _Didus_. Although the
ischiadic foramina are completed by terminal confluence of the ilium
and ischium in _Dromaius_ and _Casuarius_, yet the length of those
foramina (which are unclosed) in _Struthio_ and _Apteryx_, concomitant
with the greater relative length of the pelvis, shows the difference of
_Didus_ from the cursorial Brevipennates in this part of the skeleton.
The ischia of the winged Pigeons resemble those of the Dodo; but the
inner longitudinal ridge is more strongly marked in _Didunculus_: in
the _Goura_ it is less developed than in _Didus_; the bone is longer
also in proportion to its breadth, and the ischiadic foramen is longer
and narrower: the proportions of that in _Didunculus_ are more like
those in _Didus_. In _Didunculus_ the pubis coalesces with the ischium
behind the small obturator foramen, but leaves a second or posterior
elongate ischio-pubic vacuity. The greatest amount of resemblances with
the pelvis of the Dodo is found in that of different members of the
Dove-tribe.
In comparing the pelvis of the Dodo with that of the Vulture (Pl. XII.
fig. 6), we find in the latter that the first two confluent sacral
vertebræ; supporting moveable ribs are succeeded by several with short
abutting ribs, the extent of this part of the sacrum being nearly
one-half of the whole, instead of one-fourth as in _Didus_ and the
Doves. The reappearance of rib-abutments after four ribless sacrals is
in the posterior third of the sacrum, and they are continued to the end
of that bone from the last four vertebræ of the series, constituting
a very marked difference, both as to number and the character of the
vertebræ in the sacral part of the pelvis.
With regard to the iliac bones, the anterior concave track occupies
two-thirds of the extent of the bone in _Vultur_, not one-half as
in _Didus_ and most Doves; the breadth of the posterior parts of
the ilia with the intervening sacrum in the Vulture is relatively
less than in the winged Doves, and differs in a greater degree from
that characteristic part in the sacrum of _Didus_. In _Ciconia_ the
antacetabular part of the pelvis is relatively longer, and the iliac
bones are more expanded anteriorly. In _Platalea_ the proportions are
more nearly those in _Didus_. In _Otis_ the ilia touch the fore part of
the sacro-spinal ridge, but leave both posterior and anterior apertures
of the ilio-neural canals widely open. In _Œdicnemus_ and _Charadrius_
they are grooves, the ilia not reaching the sacral spines. The external
concavity of the ilium is longer, narrower, and deeper, in most waders,
than in _Didus_. In _Eudyptes_ and _Aptenodytes_ the ilia are more
expanded anteriorly, but the whole pelvis is narrower and longer than
in _Didus_. The Gar-fowl (_Alca impennis_)[35], _Uria_, _Podiceps_,
and _Colymbus_, all show still longer and narrower proportions of the
pelvis.
In the Doves of flight the proportions and relative position of the
three compartments of the cranial cavity differ from those in the Dodo.
Both the pros- and mes-encephalic ones are proportionally larger than
the epencephalic; and the mesencephalic compartment lies more directly
below the prosencephalic one. A very thin stratum of finely cellular
diploë divides the two tables of the skull along the medial line of
the upper surface: it is thicker between the orbits. The falcial
ridge at the inner surface of the prosencephalic roof resembles that
in _Didus_. The tentorial ridge bifurcates halfway down, the front
portion dividing, almost horizontally, the pros- from the mesencephalic
compartment, the hinder and more obtuse ridge dividing, almost
vertically, the mes- from the epencephalic compartment. The angle
of bifurcation is slightly produced and obtuse, but represents very
feebly the tentorial tuberosity (Pl. XI. fig. 1, _o_) in the Dodo: from
it, in _Goura_, is continued backward the arch of bone formed by the
superior semicircular canal, above which is the groove for the venous
sinus, as in _Didus_. The internal auditory fossa is less deep than in
_Didus_: above it is a similarly vertically oblong cerebellar pit. The
nerve-foramina correspond with those in _Didus_: the entocarotid canal
opens into a rather deeper sella in _Columba palumbus_.
On comparing the cranial cavity, as exposed by a vertical longitudinal
section in the Dodo (Pl. XI. fig. 1), with that of a Dinornis similarly
exposed[36], the first difference is the smaller proportional depth
of the diploë in the larger wingless bird, which is not greater over
the prosencephalic than over the epencephalic compartment; next
may be noticed the larger relative size of the former compartment,
indicating the larger cerebrum of the Dinornis, then the absence of
the tentorial tuberosity, the sharper and more produced superior part
of the tentorial ridge arching transversely between the cerebrum and
cerebellum, the smaller internal auditory fossa, and the deeper sella:
the mesencephalic compartment, or cavity for the optic lobe, is less in
proportion to the prosencephalic compartment than in _Didus_; it holds,
however, a similar relative position: finally, the cerebellar pit,
above the internal auditory fossa, is wanting in the Dinornis.
The Dodo agrees with the Doves in possessing a slender furculum,
forming an acute angle: it resembles _Columba galeata_, more
especially, in the halves of that bone being united by ligament below,
and forming separate styles or “clavicles.”
The humerus of the Goura closely repeats most of the characters
described in that of the Dodo; but its length is proportionally
greater, being 3 inches 9 lines, nearly equal to that of the sternum or
pelvis, whereas the humerus of the Dodo is little more than half the
length of either sternum or pelvis. The processes for the attachment of
the muscles are, nevertheless, fully as strongly developed in _Didus_
(Pl. VIII. figs. 12 & 14) as in the volant Doves (Pl. XII. figs. 8 &
9, _Goura_); that, indeed, which is a ridge (_r_) on the back part of
the shaft in _Didus_, is a mere rough surface in _Goura_, and does not
show in _Didunculus_. The pneumatic fossa, which varies in depth in
the two humeri of the Dodo, is in both relatively larger and shallower
than in _Goura_. The pectoral process is thinner, but relatively rather
more produced, in _Didunculus_. The humerus in _Œdicnemus_, _Otis_,
and _Charadrius_ has a more longitudinally extended, thinner, and more
produced pectoral ridge than in _Didus_ and the _Columbidæ_; there is a
more marked ectocondyloid tuberosity, which in _Charadrius_ becomes a
pointed process.
There is nothing to be gained by giving the details of the more
striking differences which the humerus presents in Penguins, Auks,
and birds of prey, as compared with that bone in the Dodo; but a few
words may be recorded of the comparison of the humerus of the Dodo
with that of the flightless bird of New Zealand so nearly approaching
to it in size, which bird is described in the 5th volume of the
‘Transactions’ of the Society under the name of _Cnemiornis_ (p. 395,
pl. 66. figs. 7–10). In that extinct species, although the humerus is
5½ inches in length, the parts indicative of the forces by which it
was worked are comparatively feebly developed. The ulnar tuberosity
is narrower, thicker, more obtuse, and its base has neither the upper
nor lower excavation; it rises above the articular head, which is less
prominent and narrower than in _Didus_; the pectoral ridge is shorter
and situated lower down upon the shaft, not on the same level with
the radial tuberosity as it is in _Didus_; the distal articulation is
of the same size as in _Didus_, but neither the radial nor the ulnar
convexity is so prominent or well-defined.
The ulna of the Dodo is shorter absolutely, and much more so
proportionally, than in the Goura and most other volant Doves. In
these it exceeds the humerus by about one-fourth its own length; in
_Didunculus_ (Pl. III.) it is a little longer than the humerus; in the
Dodo (ib.) it is shorter than the humerus. The length of the ulna in
_Goura coronata_ is 4 inches 6 lines; it is more bent than in the Dodo;
the quill-tubercles, seven or eight in number, are more prominent;
nevertheless the rough depression for the insertion of the chief flexor
is less deep and less defined. The plumed winglet of the Dodo would
seem, therefore, to have been frequently and forcibly moved.
In comparing the femur of the Dodo with that of the largest Dove, the
bone appears gigantic. The length of the femur in _Goura coronata_
(Pl. XII. fig. 11) is but 3 inches 3 lines, and it is more slender in
proportion to its length than in the Dodo; it, however, repeats the
few characteristics, if they may be so termed, of the Dodo’s femur. It
has the pneumatic foramen in the same position, perhaps proportionally
larger; it has the same large oblong surface for the ligament at
the head of the bone; the great trochanter has the same form and
disposition, but is not quite so much produced anteriorly; there is a
slight depression instead of a ridge for the trochanter minor; the fore
part of the inner condyle is relatively thicker and less produced. The
femur in _Otis_ and _Œdicnemus_ has a thicker and shorter trochanter
major, & more narrow and shallow rotular channel; it is shorter in
comparison with the tibia, and more especially with the metatarsus,
than in _Didus_ and the Doves.
The femur of _Aptornis otidiformis_[37] is of the same size as that
of the Dodo; but it has no pneumatic foramen, the head is more
hemispheroid and inclined forward, the ligamentous pit is deeper and
more circular, the supracervical articular surface is not defined from
that of the head, there is a wider and deeper depression at the fore
part of the proximal end of the femur, and a more prominent tuberosity
on the back part; the ridge continued from the back part of the
shaft to that of the inner condyle is more produced and sharper in
_Aptornis_, the fore part of the same condyle is less produced.
The femur in _Cnemiornis_[38] and _Dinornis_[39] is much thicker, in
proportion to its length, than in either _Aptornis_ or _Didus_. In
_Pezophaps_ the great trochanterian ridge rises higher above the neck,
and the shaft has a more uniform thickness, with the inner contour less
concave, than in _Didus_.
The characters which have been noted at the proximal and distal ends of
the tibia of _Didus_ are repeated in those of the tibia of the _Goura_.
The difference in size is more marked than in the femur; the length of
the tibia of _Goura coronata_ is 4 inches 7 lines, and its shaft is
more slender, in proportion to its length (Pl. XII. fig. 13), than in
_Didus_ (Pl. X.). The tendency to a trihedral form of the shaft is less
marked in _Goura_; the anterior prominences of the distal condyles are
thicker in proportion to the intervening fossa.
In the Vulture the fibular ridge is more parallel with the long axis of
the shaft than in _Didus_; the tendinal canal is less cylindrical, has
an oblique course from the middle of the anterior surface towards the
inner condyle; the fore parts of both distal condyles are less produced
and less convex; the distal end is narrower from before backwards
in proportion to its breadth; both extremities of the bone are less
expanded in proportion to the shaft than in the Dodo.