108 OSTEOLOGY [Parr II. 
in the thick peduncle forming the ecto-calcaneal process; in Pigeons and Pterocles, the ento-calcaneal 
process is thicker, and the tube terminates on the outer side of the buttress, which is continuous with that 
process. In Pferocles and in all the typical Gad/ing, the inner trochlea is somewhat more elevated than the 
external; but in the Cracida, it is more depressed. In the breadth of the inferior extremity, in the 
greater equality in size of the trochlee, and in the great depression of the internal, beneath the level 
of the external one, the metatarsus of MJegapodius approaches nearest to that in the terrestrial Pigeons. 
The variation in form and relative size of the surfaces giving attachment to the inter-osseous muscles, 
need not be dwelt upon here. The groove transmitting the tendon of the J. adductor annularis is in many 
of the Gadling converted into a canal by an osseous floor, asin certain Pigeons, both terrestrial and arboreal. 
The principal point, then, in which the metatarsus of the Dodo differs from that in the ordinary Gad/ine, is 
the greater development of the calcaneal buttress, which terminates superiorly in the ento-calcaneal process. 
In the American Vulture (Cathartes Californianus), the metatarsus is compressed in the antero-poste- 
rior diameter, and deeply excavated in front, beneath the proximal extremity ; the section of the shaft, both 
above and below, is therefore transversely oblong. The outer segment of the posterior surface is trans- 
versely subconcave; the calcaneal process is depressed, broad, and imperforate, presenting two broad 
shallow grooves posteriorly ; from its centre extends downwards a moderately developed ridge subsiding 
towards the middle of the shaft ; the external trochlea is more depressed than in the Dodo. 
In the Vulture (Gyps fulvus) and Eagle (Haliaétus albicilla), the shaft of the metatarsus is sub- 
triedal, and the broad posterior surface presents a shallow groove in its whole extent. The wide, vertically 
concave, external border looks directly outwards in the Eagle, but in the Vulture has an inclination forwards 
and inwards; and the anterior surface slopes rapidly backwards towards the internal edge. The surfaces 
for the origin of the I. MW. adductor indicis and extensor medii are very small, while that for the 
Extensor pollicis occupies the upper half of the anterior surface. The various grooves and tubes for the 
transmission of the flexor tendons in the Dodo and Pigeons, as well as in the Gallina, are represented by 
a single, deep, semilunar notch extending from the subquadrate plate, representing the ento-calcaneal pro- 
cess, to a prominent tubercle forming the outer and posterior angle of the proximal articular extremity ; 
“this process is not supported by a ridge descending on the posterior surface of the shaft, it is only a litle 
more extended downwards basally, than at its free flattened extremity. 
Inthe Vulture, the trochleze are more nearly on a level ; the external, as in Cathartes, bemg much lower 
than in the Dodo and terrestrial Pigeons. In the Eagle, the trochlez are relatively narrower ; the inner is 
placed on the same plane as the middle one, and its internal and posterior angle is more produced than in 
the Dodo and other Pigeons, or thanin Cathartes. The inter-condyloid tubercle is relatively very small in 
the Vulture and Eagle. | While the metatarsus in the Dodo is distinguished from that of the ordinary 
Galline, only by a few and comparatively slight peculiarities, in which it approaches the typical Pigeons, it 
differs from the corresponding bone in the Vulture and Hagle, in the form of the shaft ; in the presence 
of the complex ecto-calcaneal process, and of the highly developed calcaneal buttress ; and in the greater 
elevation of the external trochlea: poimts of distinction so important as, even overlooking innumerable 
minor dissimilarities, to preclude any idea of the affinity of the Dodo to these raptorial forms. The 
metatarsus of the Dodo, in the presence of the calcaneal buttress, resembles that of Cathartes more than 
its homologue in the less aberrant raptorial birds; but this will not outweigh other important differ- 
ences, and is such as not to indicate affinity, but simply a general resemblance in mechanical construction. 
