internal trochlea, which is intermediate in size between the middle and external ones, the former being the
larger, has its axis directed inwards, and is placed obliquely at the apex of a right triangular stem, which
projects inwards, beyond a line drawn perpendicularly from the inner margin of the central part of the
shaft; its inferior and internal margin is about a line above the plane of the middle trochlea; in front it is
convex transversely, but its posterior and internal angle is elongated backwards and inwards, rendering it
deeply concave behind. The middle trochlea is deeply grooved; the inner condyle is the most prominent
anteriorly, but the external, below and behind; the groove expands, at its termination in front, into a sub-
circular fossa impressing the stem. The outer trochlea anteriorly is more abruptly defined than the inner,
and is slightly grooved; behind, the narrow outer condyle projects greatly. The sides of the trochlea are
impressed with deep pits for the insertion of the strong lateral ligaments.
The metatarsus in the smaller Pigeons, and especially in the shorter limbed arboreal species as Treron,
Lopholeemus, &c., has nearly the same form as that in the Dodo; but in many of the ground Pigeons
(Gourinre), it is relatively longer and more slender.
In Treron (Plate XI. Pig. 32-36), the inner metatarsal element is narrowed and flattened beneath
the proximal extremity for the origin of the M. extensor collide, so as to look almost directly inwards; and
the surface for the df. adductor annularis is relatively smaller, and also not visible from beforei In Lopho-
leemus (ib. Pig. 88-42) and Carpophaga, the muscular surfaces are nearly as in the Dodo. The internal
inter-osseous foramen is relatively larger, and the tibialis tubercle more remote from it than in the Dodo. In
Treron, the trochlese are nearly in the same curve, so also in Lopholeemus, and still more distinctly in Carpophaga
; in all these, however, the inner trochlea is perceptibly more elevated than the outer. The outer
edge is acute, forming a ridge separating the surfaces for the M. M. adductor and abductor annularis,
and the areas which give origin to the M. M. abductor annularis and abductor iudncis, are thus increased,
especially that for the latter. In Lopholeemus, the large articular facet for the posterior metatarsal is placed
nearly in the centre of the shaft; in Treron and Ca/rpophaga, a little below it. In all the typical arboreal
Pigeons, the ento-calcaneal process is elongated upwards at its expanded extremity; its upper edge is
therefore concave (ib. Pig. 34, 40), not straight as in .the Dodo; it also projects more than in the Dodo,
and thus gives the M. gastrocnemius increased leverage. In Lopholeemus (ib. Pig. 41) and Carpophaga, the
sculpturing of the ecto-calcaneal process is the same as in the Dodo ; in Treron (ib. Pig. 35), the groove
for the perforated tendons of the inner toe is converted into a canal. In Lopholeemus, the groove
lodging the tendon of the M. adductor annularis is converted into a canal by an osseous bridge, leaving
above it an aperture leading directly from the anterior to the posterior surface. In Treron and Carpophaga,
the sharp posterior edge of the calcaneal buttress is slightly notched.
In Cobmba (Plate XII. Pig. 7), which represents a group intermediate, in habits and in the structure
of the foot, between the arboreal and ground Pigeons, the form of the metatarsus so much resembles that in
the Dodo, that it is difficult to specify the slight differences which exist. The outer border, uncovered by
muscle, is broad like that in the Dodo, and twines round the outer metatarsal element, so as to appear on
the anterior surface beneath the proximal extremity; this causes a diminution of the surfaces for the
M. M. abductor annularis and abductor imdicis, especially that for the latter. The upper border of the
ento-calcaneal process is straight; the form of the ecto-calcaneal process is as in the Dodo, but the ridge
separating the groove for the tendon of the M. flexor perforaus pollicis from that for the tendon of the
Peroneus medius, is more developed, and has a tendency to convert the former into a canal. The inner
trochlea is less depressed than in the Dodo, the relative levels of the pullies being nearly as in Treron &c.
This bone may be readily procured, for comparison with the figures of the metatarsiis of the Dodo.
In Lidunculus (Plate X. Pig. 9-9 e), and Phaps (Plate XI. Pig. 20-24), the metatarsus is
elongated and slender, being of equal length in both, while they closely resemble each other in form and
proportion; in each, the flattened outer border is still broader than in Cobmba, and the surfaces for the
M. M. abductor a/mularis and abductor i/ndicis are hence more reduced, from the encroachment of this
border, which is widest in the centre, and contracts slightly downwards towards the inner trochlea. The
area for the M. extensor pollicis is relatively larger than in the arboreal Pigeons. The upper border of the
ento-calcaneal process is straight in both; in Diduuculus, the groove for the tendon of the M. flexor perforans
pollicis is converted into a canal (Plate X. Pig. 9 d), and that for the tendons of the perforated flexors of
the inner toe, is also nearly closed. In Phaps, the outer ridge of the groove for the M. flexor perforans pollicis
is very apparent, as in Cobmba. In Diduuculus, the trochlese are arranged exactly as in the Dodo; the
groove for the tendon of the M. adductor annularis, is covered posteriorly by an osseous band, as in Lopholeemus,
and in Phaps, where it is narrower. In Phaps, the inner trochlea is more elevated than in the
Dodo, but the outer is more abbreviated than in Dicbmculus, and more like that in the Dodo; the posterior
metatarsal facet in both, is placed below the junction of the lower with the upper two-thirds of the bone.
The elongation and relative slenderness of the metatarsus, the great breadth and flatness of the outer
border, and the position of the articular facet, are reproduced in the Solitaire; and the inner margin,
which is acute in Diduuculus, is replaced in Phaps, by a narrow plane as in the Solitaire.
In Geophaps (Plate XI. Pig. 26-30. Plate XII. Pig. 8), the metatarsus is shorter and more robust
t.Wi in the two preceding species; and the outer margin, which is broad above, passes in the lower
third of the shaft, into a narrow ridge separating the surfaces for the M. M. adductor and abductor
annularis. The arrangement of the trochlese is precisely the same as in the Dodo. In Geophaps, Phaps, and
Diduuculus, the tibialis tubercle encroaches on the inner inter-osseous foramen, as in the Solitaire, while in
the Dodo, it is lower down. In Geophaps, as in Diduuculus, the grooves for the perforated tendons of
the inner toe, and the deep flexor tendon of the hind toe, are converted into canals.
In Gcwra (Plate XI. Pig. 11-15), the metatarsus has nearly the same form as in Phaps, but the outer
border is relatively narrower. In Phaps, Geophaps, and Goura, the ecto-calcaneal, however, is thicker than
in the Dodo, &c., and is grooved externally for the tendon of the deep flexor of the hind toe.
Prom these details we may therefore conclude, that the metatarsus of the Dodo possesses the family
characters of that bone in the Columbidee.
In the typical Gallunee, the calcaneal buttress is feebly developed and speedily subsides, and the shaft is
thus more compressed in the antero-posterior diameter; it is, however, as strongly marked as in Pigeons, in
the short and robust prismatic metatarsus of Pterocles; and it is more apparent in the Cracielee and Megapodida
than in the common Cock. The external segment of the posterior surface is subconcave transversely, except
in Pterocles. The ridge which supports the spur also distinguishes the metatarsus in the typical genera of the
Gallunee; that peculiar appendage is not the homologue of the hallux, as has often been supposed. Swainson
long ago pointed out its true nature; it is really a portion of the dermo-skeleton, which becomes united to the
metatarsal element of the ento-skeleton, by an extension of the ossific process in the intervening ligamentous
texture; just as the teeth, which belong to the splanchnic division of the exo-skeleton, become anchylosed to
the jaws in several fishes and reptiles. The hiud toe is the true hallux, and is present in the great majority
of birds. It has the normal number of phalanges, namely, two, and is supported by the accessory
metatarsus; the outer, or fifth toe, is invariably absent in birds. In most of the Gallvna, the tube which
transmits the tendon of the M. flexor dhgitorumperforans pierces, as it were, the thickness of the ento-calcaneal
process, and opens below upon, or to the inner side of the calcaneal buttress, which runs up to terminate
2 F