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Show 1903.] OSTEOLOGY OF THE CUCULIFORMES. 281 backwards into an obliquely sloping bar. The pubis is long, slender, and much bowed and closely bound to the posterior half of the ventral border of the ischium, beyond which it extends for some considerable distance. The obturator foramen is bounded posteriorly by a broad bar of bone descending from the ischium and fusing with the pubis. The pectineal process is reduced to a vestigial condition. In the form of the pelvis, Cuculus, Coccystes, Scythrops, differ but little, save in size, from Cacomantis merulinus. In Scythrops, however, the obturator foramen is not cut off posteriorly by the descent of a bony plate from the ischium. In all save Cacomantis and Cuculus the intertransverse sacral foramina are more or less completely filled up. In Rhopodytes and Eudynamys the mesial border of the extreme anterior end of the preacetabular ilium rises to the level of the neural ridge as in Geococcyx (text-fig. 46, p. 282). In Taccocoua this elevated region extends somewhat further backwards and forms a quadrate plate, the free border of which is lightly applied to the neural crest. In Crotophaga, Rhamphococcyx, Coua, and Piaya actual fusion takes place between this plate and the synsacrum. In Centropus and Dromococcyx the relationship between the fused region of the ilium and the synsacrum has become still further modified, so that the extremity of the ilium has acquired a T-shaped form, the dorsal limb of the cross-piece bridging a widely open canalis ilio-lumbalis. A similar canal is of course formed in the other cases where the ilia meet the neural crest of the synsacrum, but it is inconspicuous. Further modifications in the form of the pelvis are the enormous lateral expansion of the dorsal plane and the shortening of the pubis. In forms like Crotophaga, Coua, or Rhamphococcyxthe early stages of the first-mentioned modification may be studied. Passing through forms like Centropus and Taccocoua, we reach a climax in Geococcyx (text-fig. 46, p. 282). Herein the width across the dorsal plane equals the length of the synsacrum. This outward extension of the postacetabular ilium has resulted in the formation of a huge ledge passing far beyond the level of the antitrochanter, and finally, at its free edge, turning abruptly downwards and then suddenly upwards, backwards, and inwards, like a pair of wings, so that the surface of the dorsal plane acquires a peculiar saddle-shaped appearance. Seen from the side (text-fig. 47, p. 282) or from below (text-fig. 48, p. 282), this overhanging ledge forms an enormous penthouse above and slightly behind the ilio-ischiadic foramen. A similar modification obtains elsewhere only among certain Rails. It appears to be correlated with a terrestrial mode of life, these forms flying but little. The shortening of the pubis is most marked in Geococcyx, Piaya, Centropus, and Rhinococcyx, and to a less extent in Coua and Crotophaga. A large pectineal process occurs in Geococcyx, Coua, Centropus, |
