106 OSTEOLOGY [Parr II. 
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 imwards, 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 Zveron, 
Lopholemus, &e., has nearly the same form as that in the Dodo; but in many of the ground Pigeons 
(Gourina), it is relatively longer and more slender. 
In Zreron (Plate XI. Fig. 32-36), the inner metatarsal element is narrowed and flattened beneath 
the proximal extremity for the origin of the IZ. extensor pollicis, so as to look almost directly inwards ; and 
the surface for the W. adductor annularis is relatively smaller, and also not visible from before. In Lopho- 
lemus (ib. Fig. 88-42) and Carpophaga, the muscular surfaces are nearly as in the Dodo. The internal 
inter-osseous foramen is relatively larger, and the ¢ida/is tubercle more remote from it than in the Dodo. In 
Treron, the trochlee are nearly in the same curve, so also in Lopholemus, and still more distinctly in Carpo- 
phaga ; %0 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 IZ. M. adductor and abductor annularis, 
and the areas which give origin to the I. W. abductor annularis and abductor indicis, are thus increased, 
especially that for the latter. In Lopholemus, the large articular facet for the posterior metatarsal 1s placed 
nearly in the centre of the shaft; in Zreron and Carpophaga, 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 (iJ. Fig. 34, 40), not straight as in the Dodo ; it also projects more than in the Dodo, 
and thus gives the IW. gastrocnemius increased leverage. In Lopholemus (ib. Fig. 41) and Carpophaga, the 
sculpturing of the ecto-calcaneal process is the same as in the Dodo ; in Zreron (ib. Fig. 35), the groove 
for the perforated tendons of the inner toe is converted into a canal. In Lopholamus, the groove 
lodging the tendon of the MZ. 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 Zreron and Carpophaga, 
the sharp posterior edge of the calcaneal buttress is slightly notched. 
In Columba (Plate XU. Fig. 7), which represents a group intermediate, in habits and im 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 twimes 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 indicis, 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 IZ. flexor perforans 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, &e. 
This bone may be readily procured, for comparison with the figures of the metatarsus of the Dodo. 
