Dodo, two measure 6 inches 3 lines in length; one (Pl. IX.) is 6 inches
4½ lines; the shortest is a little under 6 inches, with proportionate
differences in the diameter of the shaft. All of them show a small
pneumatic foramen (Pl. IX. figs. 1 & 2, _p_) on the inner side of the
anterior ridge of the great trochanter (ib. _c_), and on the same
transverse line with the head of the bone. This part shows an oblong
depression (ib. figs. 2 & 3, _a_) for the “ligamentum teres” at the
upper and back part. The articular surface on the same aspect of the
neck (ib. fig. 3, _b_), adapted to the trochanterian prominence of the
pelvis (Pl. VII. _t_), is well-defined. The trochanter (Pl. IX. fig. 1,
_c_) rises, ridge-like, above the level of the head, and is continued
from behind the middle of the articular surface on the neck, forward,
with a convex outline upon the fore and outer part of the shaft, where
it gradually subsides; a narrow intermuscular ridge (ib. fig. 1, _r_),
inclining to the middle of the fore part of the shaft, is continued
from the trochanterian one. The small trochanter (ib. fig. 3, _d_)
is a small subcircular tuberosity, in some specimens a ridge, 3 to 4
lines in length, on the inner side of the shaft, about an inch below
the head. The muscular impressions on the fore part of the bone are
well defined. A minute medullary canal (ib. fig. 3, _m_) perforates the
middle of the back part of the shaft; the popliteal fossa (ib. fig.
3, _o_) shows a few small pneumatic orifices; a triangular rough flat
surface divides the fossa from the outer condyle. Above the fibular
depression (ib. fig. 3, _g_) there is a well-defined, slightly raised,
rough surface (ib. _k_) for the head of the ectogastrocnemius muscle.
The ridge (ib. _n_) extending to the back part of the inner condyle is
not sharp; the rotular groove (ib. fig. 1, _p_) is deep and moderately
wide, with the inner boundary, formed by the narrow anterior part of
the inner condyle (ib. fig. 5, _e′_), most produced. The breadth of
this end of the longer femora is 1 inch 9 lines; the character of the
distal articular surface is shown in Pl. IX. fig. 5.
The head, neck, and great trochanter (Pl. XI. fig. 6) are occupied by a
pneumatic cancellous structure, with a thin compact wall on the upper
part and sides: this begins to gain thickness at the under part of the
neck and at the lower and back part of the trochanter, the compact wall
acquiring a thickness of a line at the beginning of the shaft, where
the cancellous structure is confined to the outer side of the pneumatic
cavity; this structure gives way to a few delicate filaments of bone
crossing the cavity of the major part of the shaft, and is not resumed
until the bone expands to form the distal condyles (ib. fig. 7).
The five _tibiæ_ of _Didus_ in the same collection range in length from
8 inches 8 lines to 9 inches. The procnemial ridge (Pl. X. figs. 1,
2, 4, _p_) is a triangular plate, with the base longest and the apex
rounded off: it inclines outwardly, and does not extend much more than
half an inch from the level of the proximal end of the bone: the length
of its base rather exceeds an inch: on its inner side a triangular
muscular surface is well defined by an irregular inferior line or ridge
(ib. fig. 2, _n_). The ectocnemial process (ib. figs. 1, 3, 4, _e_)
is thicker, shorter, and terminates roughly and obtusely. There is a
low, narrow ridge (ib. fig. 2, _g_), about half an inch in length, on
the inner side of the proximal end of the shaft, beginning about 9
lines below the articular surface at that end. The fibular ridge (ib.
figs. 1 & 3, _h_), beginning 1 inch 8 lines from the proximal end,
extends about 2 inches down the outer side of the shaft. The epicnemial
ridge (ib. figs. 1 & 4, _k_) is obtuse, and but little produced above
the upper articular surfaces or condyles (_t_ _d_) of the tibia: the
breadth of that end of the bone, in the longest specimen, is 2 inches 3
lines. The tendinal canal at the fore part of the distal end is bridged
by bone (ib. fig. 1, _l_), and is situated on the inner half of that
aspect of the shaft; the lower opening is subcircular and close to
the anterior end of the inner lower condyle (ib. _a_), which is more
produced forward than the outer one (ib. _b_). Their hind ends project
very little beyond the level of that aspect of the shaft of the tibia.
An intermuscular ridge (ib. fig. 1, _r_) strengthens into a tuberosity
(_r′_) at the inner side of the tendinal groove.
The cancellous structure in the tibia is limited to an extent of about
half an inch below the proximal articular surfaces (Pl. XI. fig.
8), and to about an inch and a half from the distal end of the line
(ib. fig. 9): the shaft is occupied by a large air-cavity, with a
compact wall of half a line in thickness at the upper third, gradually
increasing to about a line at the lower fourth, until the cancellous
structure is reestablished; the transverse direction of a plate of this
structure indicates the extent of the original distal epiphysis of the
tibia (fig. 8).
The _fibula_ (Pl. X. figs. 6–8) presents the usual ornithic characters
of the bone: it varies from 4 inches 4 lines to 4 inches 6 lines in
length, with a greatest proximal breadth of 8 lines. No adequate gain
would result from a detailed description or comparison of this bone;
and the rest of the bones of the foot have received every requisite
attention in this way in the excellent work on the Dodo and its
kindred, already quoted. A longitudinal section of the _metatarsus_,
taken in the direction from side to side (Pl. XI. fig. 10), shows
the loose cancellous texture of the common epiphysis of the three
long metatarsals, and the remnant of their contiguous coalesced walls
reduced to a thin lamella of bone. As the moiety of the bone figured is
the posterior one (of the left metatarsus), the usual oblique position
of the middle metatarsal (_iii_), with its proximal end nearer the back
part and its distal end nearer the fore part of the coalesced series,
produces a corresponding direction of the section, with narrowing and
termination of the exposed part of the medullary canal about one-third
from the distal end of that metatarsal. The medullary canal of the
outer metatarsal (_iv_) is wider and descends lower before the breaking
up of the inner surface into decussating lamellæ or filaments, than
that of the inner metatarsal (_ii_): the peripheral compact wall of the
inner is twice the thickness of that of the outer metatarsal. I may
remark that the more posterior position of the middle metatarsal at
its proximal end, from which and the corresponding part of the common
epiphysis the calcaneal process is developed, is related to the greater
share taken by the middle toe in the act of walking and scratching. I
will only remark that of the four metatarsals of as many Dodos in the
present series, one exceeds by a line the length of that figured in
plate xi. _op. cit._, and one falls short thereof to the same trifling
amount.
_Skull._ (Plates III. & XI. fig. 1.)
Of the skull of the Dodo, the series of bones transmitted to me include
the cranial part with the detached upper mandibular bone (more or
less mutilated) of two mature birds, and the lower mandible of three
individuals. In the latter the dentary elements (Pl. XI. fig. 1, 32),
confluent at the “gonys,” are distinct from the hinder halves of the
rami formed by the confluent, or perhaps connate, articular, surangular
and angular elements (ib. 31): if the “splenial” were ever distinct, it
has coalesced with the dentary, where its upper boundary is indicated
by a linear groove or series of small foramina.
In size, shape, and all other characters of these important evidences
of the specific nature of the remains from the Mahébourg morass[29],
they agree with those of _Didus ineptus_ detailed in the ‘Proceedings
of the Zoological Society’ for January 11th, 1848 (part xvi. pp. 2–8),
and in the work entitled “The Dodo and its Kindred,” pp. 76–96.
The occipital condyle (ib. 1) presents the same hemispheroid or
reniform shape, with the median vertical notch or depression above.
The upper margin of the foramen magnum is broad, as it were excised,
with the sides slightly prominent. The superoccipital foramen is
present in both specimens, as in the one originally described (Proc.
Zool. Soc. part xvi. p. 2). This foramen also exists in Owls and
Parrots, but not in all Pigeons; the _Didunculus_ (Pl. III. fig. 2)
shows no trace of it; I have also failed to find it in the skull of a
Crown-pigeon (_Goura coronata_). The superoccipital ridge is defined by
the subsidence of the surface beneath it being continued directly from
the upper, almost flat, smooth surface of the cranium: the middle part
of the ridge is more produced than the angles. In the great breadth of
the occipital surface compared with its depth, in its flatness from
side to side, and its aspect backward and a little upward, _Didus_ most
resembles _Dinornis_. The basioccipital curves downward, and unites
with the basisphenoid in developing the pair of larger tuberosities
(Pl. XI. fig. 1, 5), which terminate about ½ an inch below the
occipital condyle. There is nothing of this structure in the Columbine
cranium. In one of my Dodo’s skulls there is a pair of small tubercles
between the larger basioccipital ones; these are not developed in the
other cranium. The basisphenoid is subquadrate, and flattish below,
impressed by a shallow median longitudinal channel.
The hypoglossal nerve escapes by two small foramina on each side of
the base of the condyle; external to these is the vagal foramen; still
more external is the depression (ib. _a_) perforated below by the
entocarotid, glossopharyngeal, and sympathetic, above by the tympanic
vein. The entocarotid canal opens into the hind part of the sella or
pituitary fossa: the vagal canal begins within the skull, above the
hypoglossal foramina. The paroccipital carries the posterior surface
of the skull downward and outward to a much greater degree than in any
Dove, but to a less degree than in _Dinornis_. The Eustachian tubes
impress the outer and fore part of the basisphenoid.
The temporal fossæ (Pl. III.), in the present specimens, show the same
contraction in proportion to their depth by which the original skull
of the Dodo, compared with that of the _Dinornis_, ‘Proc. Zool. Soc.’
(1848, p. 3), differed from the larger extinct wingless bird. In the
approximation of the postorbital process to the mastoid, _Didunculus_
shows a closer resemblance to _Didus_ than does _Goura_, in which the
temporal fossa, besides being narrow, is shallow. The temporal muscle
appears to spread its origin above the fossa upon the sides of the
cranium, forward half an inch in advance of the postfrontal process,
and backward to the outer angle of the superoccipital ridge.
The parietal region is broad, flat, and short, as in _Dinornis_, not
convex as in Doves; it is also impressed at its middle part by a
shallow transverse groove, continued outward and forward of less depth
and definition, so as to mark off the convex interorbital part of the
swollen frontals.
The outer side of the mastoid is convex, smooth, overhanging the
tympanic cavity, and sending off a short process, the base of which is
defined in one cranium by a transverse ridge in front of the anterior
articular cup for the tympanic bone. A similar process is developed in
_Didunculus_, not in _Goura_, where it is barely indicated.
The presphenoid is compressed, but thickened and rounded below, where
the palatines and pterygoids at their junction with each other abut
against it: the pterygoid sends off a short process from the middle of
its hinder border; but this is not met by a corresponding “pterygoid
process” of the basisphenoid as in _Didunculus_.
The frontals are broad and convex, rising abruptly (as in _Didunculus_)
above the coalesced cranial ends of the nasals and premaxillary (Pl.
III.); in _Didus_ the breadth greatly exceeds the length of the
interorbital frontal convexity, as compared with _Didunculus_, and the
convexity reigns in the transverse as well as the antero-posterior
direction; in _Didunculus_, however, it is less concave transversely
than in _Goura_. In the breadth or thickness of the interorbital
septum _Didus_ resembles _Apteryx_ and _Palapteryx_ and shows the
same pneumatic cancellous structure. The posterior olfactory chambers
are partially divided, as in _Dinornis_, by an upper median septum;
each compartment, which is 7 lines across and an inch in length, is
perforated posteriorly by an olfactory foramen more than a line in
diameter, from which grooved impressions of ramifications of the nerve
diverge upon the hind and upper wall of the chamber: external to the
olfactory foramen is a longer one for the passage of a vein into the
fore and inner part of the orbit.
The cranial ends of the nasals and nasal process of the premaxillary
(Pl. XI. fig. 1, 22) are flat, depressed, thin plates; the latter at
its junction with the frontal is 6 lines broad, partially divided by
a median groove above and a ridge below, and by short linear fissures
from the nasals: the forward extension of these bones is feebly
indicated by linear grooves terminating at the outer margins of the
nasal branch of the premaxillary, about 4 inches from its vertical
end. The proportion of the base of the upper mandible attached to the
frontal contributed by the nasals is the same as that indicated in
the ‘Proc. Zool. Soc.’ _l. c._ The nasal branch of the premaxillary
presents a full elliptical transverse section where it quits the
maxillary processes, losing both depth and breadth as it recedes
to join the nasals; here it retains its breadth, viz. 6 lines, but
continues to be thinned off vertically to the plate above named joining
the frontal. The under surface of the narrower part of the stem is
angular, the upper one being gently convex.
“Where the nasal and maxillary processes diverge, there is a deep
groove externally, terminating in a canal directed forwards into
the rostral part or body of the premaxillary”[30]. This part is
subdecurved, pointed, roughened by irregular vascular perforations and
grooves, with a sharp alveolar border, which describes a sigmoid curve
lengthwise, and with a deeper concavity of the palatal surface than in
_Dinornis_ or _Didunculus_. Moreover the concavity is partially divided
lengthwise by a median ridge. The palatal surfaces of the maxillary
processes and maxillaries are narrow and very convex transversely,
intercepting a long narrow palato-nasal fissure. The outer side of the
maxillary process is deep vertically and slightly concave lengthwise—a
structure not known in _Didunculus_ or any Dove, and related, like
most other deviations from the Columbine cranial characteristics, to
the provision of unwonted strength of beak in the Dodo. The maxillary
branches of the premaxillary have completely coalesced with the
maxillaries, as these have with the palatines; and the halves of the
upper mandible here swell out laterally and more so vertically, the
maxillaries rising to combine with the outer divisions of the nasals,
and sending back a short process from their lower and lateral part to
join the malar. The inner surface of the maxillary process (Pl. XI.
fig. 1, 22*) is smooth and slightly convex vertically; both upper and
lower borders are obtuse and thick.
The palatines arch outward from their posterior attachments, are broad
and smooth mesially; the margin here is angular, with a slightly
produced obtuse apex, divided by a channel on the under surface of
the palatine from the outer convex border; the upper and outer ridge
extends forward to the maxillary; the inner one subsides before
reaching that bone. “The palatines form the posterior boundaries
of the naso-palatine aperture, and approximate each other at both
ends, but more closely posteriorly, yet here without meeting; whilst
in _Didunculus_ they coalesce before receiving the abutment of the
pterygoids.
“The tympanic bone is subquadrate, with the four angles produced, and
the upper and hinder are bifurcate, forming the double condyle for
the mastoid articulation”[31]. There is a larger pneumatic foramen,
communicating with the tympanic cavity, between the articulating
cavities for these condyles.
The brain is singularly small in the present species of _Didus_: and
if it be viewed as an index of intelligence of the bird, the latter
may well be termed _ineptus_. The length of the cranial cavity (Pl.
XI. fig. 1, _v_ _c_) is 1 inch 8 lines, its extreme breadth 1 inch
6 lines, its greatest height 1 inch (and this is at the cerebellar
fossa). The most remarkable feature in the cranial structure of _Didus_
is the disproportionate size of the brain-case to the important part
of the neural axis it contained and protected: some approximation to
this condition is made by _Dinornis_[32], the Owls, and a few large
Cockatoos, _e. g._ _Microglossum aterrimum_; but it is fully paralleled
only by the Elephant among air-breathing vertebrates, as may be seen
by comparing the section Pl. XI. fig. 1 with the figures of a similar
section quoted below[33].
Not only was the brain of very small proportional size in the present
large extinct bird, but the division of the cranial cavity appropriate
to the cerebrum proper is less in proportion to that for the cerebellum
and optic lobes, at least in vertical and longitudinal diameters, than
in any other known bird.
In the Elephant the thickness of the pneumatic diploë between the
fore part of the cerebral cavity and that of the outer cranial wall
equals the longitudinal diameter of the cavity containing the cerebral
hemispheres: in _Didus_ it exceeds that diameter. The thickness of the
pneumatic diploë above the cerebral cavity equals the vertical diameter
of that cavity in _Didus_: the diploë gradually decreases in thickness
as it approaches the foramen magnum. The disposition of the osseous
lamellæ forming the cells or cavities of the diploë is very different
in the Elephant and Dodo: they extend for the most part vertically
between the outer and inner tables of the skull in the proboscidian
mammal, leaving long and narrow interspaces; in the heavy ground-bird
they form a congeries of small subequal and subspherical air-cells, and
this structure obtains in the basal and lateral walls as well as in the
superior or “roofing” wall of the cranial cavity. The extent of this
cancellous structure at the sides of the cranial cavity may be known by
the ratio of the breadth of that cavity to the breadth of the cranium,
which is 3 inches and 8 lines at the broadest part of the brain, viz.
the prosencephalon. It would seem, at first sight, as if the poorly
developed brain of the Dodo had needed, on some account, unusual
protection; but the true explanation rests on the size, weight, and
power of the bill, and the concomitant necessity for adequate extent
of attachment of the facial to the cranial part of the skull, and of
the muscles from the trunk destined to sustain and wield the long and
heavy-beaked head. The cerebrum of the Dodo does not greatly, and by
no means proportionally, exceed the size of that part of the brain in
the Crown-pigeons (_Goura_). If the great Ground-dove of the Mauritius
gradually gained bulk in the long course of successive generations in
that uninhabited thickly-wooded island, and, exempt from the attacks
of any enemy, with food enough scattered over the ground, ceased to
exert the wings to raise the heavy trunk, then, on Lamarck’s principle,
the disused members would atrophy, while the hind limbs, through the
increased exercise by habitual motion on land, with increasing weight
to support, would hypertrophy.
In the long course of generations subject to this slow rate of
change, there would be nothing in the contemporaneous condition of
the Mauritian fauna to alarm or in any way to put the Dodo to its
wits; being, like other Pigeons, monogamous, the excitement, even, of
a seasonal or prenuptial combat, might, as in them, be wanting: we
may well suppose the bird to go on feeding and breeding in a lazy,
stupid fashion, without call or stimulus to any growth of cerebrum
proportionate to the gradually accruing increment of the bulk of
the body. Whatever part of the brain was concerned in regulating or
controlling muscular actions, might, indeed, be expected to show some
concurrent rate of increase with the growing mass of the voluntary
contractile fibres; and the size of the cerebellar division (Pl. XI.
fig. 1, _n_ _o_) of the cranial cavity accords with the generally
accepted physiology of the superincumbent mass of the epencephalon.
The lateral depression at the fore and under part of the side of the
postcerebral division of the cranial cavity indicates that the optic
lobes, like the eyes, remained almost stationary during the progressive
acquisition of the bulk that distinguishes the Dodo from the largest
existing Doves.
The proportions of _Didus_, _Pezophaps_, _Casuarius_, _Rhea_,
_Dromaius_, _Struthio_, _Aptornis_, _Cnemiornis_, _Palapteryx_,
_Æpyornis_, _Dinornis_, &c. among terrestrial birds, of _Notornis_
among the lake-haunting Coots, and of _Aptenodytes_ and _Alca impennis_
among seabirds, point to the disuse of wings in flight as the main
condition of increase of size in species of birds—the next condition
being absence of lethal enemies during the years requisite for such
course and rate of growth.
Let foes arise from whom a power of flight is the main condition of
escape, and the wingless giants of the feathered class soon succumb.
Among the genera above-cited, _Aptornis_, _Cnemiornis_, _Æpyornis_,
_Palapteryx_, _Dinornis_, _Didus_, and _Pezophaps_, with the largest
of the Auks, have thus passed away, while _Notornis_ and _Apteryx_ are
on the verge of extinction through the rapid increase of population
in the small island to which they are restricted. In sparsely peopled
continents, such as Africa, South America, and Australia, brevipennate
giants may still range the deserts, pampas, and unfrequented wilds. The
ascertained recent advent of Man in New Zealand, New Britain, Ceram,
Banda, Salwattie, Mauritius, Rodriguez, significantly points to the
conditions under which have come to pass, in lapse of time, so strange
an anomaly as a bird with the specially modified instruments of flight
reduced below the power of exerting that mode of locomotion, yet, as
a bird, retaining the conditions of the respiratory and tegumentary
systems of the volant class, of which it has become a degenerate
member. With the cessation of the chief of those conditions, viz. the
absence of enemies, such birds necessarily perish.
Refraining, however, from further indulgence in an easy and seductive
vein of speculation, I would recall attention to the notable
protuberance in the cranial cavity of the Dodo (Pl. XI. fig. 1, _o_)
developed towards the upper part of the vertical tentorium, contracting
at its lower part into the ridge dividing the prosencephalic from
the mesencephalic chamber. In the latter are the orifices for the
issue of the trigeminal nerve, the larger and posterior (ib. _tr_)
giving passage to the third and second divisions, and answering to the
combined foramen ovale and rotundum of mammals, and the smaller and
anterior foramen dismissing the first or orbital division of the fifth
nerve. At the upper part of the mesencephalic fossa the narrow groove
for the lateral venous sinus impresses and defines the back part of the
tentorial protuberance, above which it bifurcates, the lower branch
bounding or defining the wall of the superior semicircular canal and
the upper part of the primitive acoustic capsule. Below this arch is
an oblong cerebellar fossa (ib. _n_) which appears to have received
veins from the cranial diploë. Beneath this fossa, and just behind
the mesencephalic chamber, is the multiperforate internal auditory
depression. Next behind this is the outlet for the vagal nerve and
entojugular vein. Below this are the small precondyloid foramina. There
is a falcial ridge, low and thick, indicating the division of the
prosencephalic chamber into lateral compartments for hemispheres; and
this ridge shows a narrow groove as for a small longitudinal sinus. A
transverse linear groove abruptly defines the fore part of the ridge.
The vertically expanded anterior part of the premaxillary (ib. fig. 1,
22) has a large pneumatic cavity communicating by a reticulate wall
with the cells of a cancellous structure, larger than those of the
cranial diploë. The maxillary branch of the premaxillary (ib. 22*)
consists of a light open-work air-diploë, with a very thin outer case
of bone. The short symphysis mandibulæ shows a small cavity, surrounded
by more minutely cancellous structure and thicker compact walls,
especially at the upper and hinder parts.