OCR Text |
Show 1903.] OSTEOLOGY OF THE CUCULI FORMES. 285 up the shaft, and has the glenoid articular surface conspicuously laterally compressed and twisted, so as to cross the long axis of the shaft transversely. This limb may be readily distinguished from that of the Psittaci, inasmuch as in the latter the trochlea of D. II. stands out at right angles to the tarso-metatarsal shaft, whilst the trochlea for D. IV. lias rotated so that its articular surface is turned to look directly backwards. Thus, the outer condyle comes to lie next the shaft, and, furthermore, is produced into a liook-sliaped process of considerable size. Amongst the Coraciiformes, probably the pelvic limb of Leptosoma most nearly resembles that of the Cuculiformes, but the conspicuously higher position 011 the shaft of the trochlea of I). IV., which obtains in this last group, is sufficient to prevent confusion. The fibular ridge is confined to the upper end of the shaft, and increases in depth from above downwards. The length of the fibula may vary considerably even in different species of the same genus. Usually it is greatly reduced, but in Centropus toulou, for example, it extends considerably beyond the middle of the tibial shaft, whilst in C. madagascariensis it falls considerably short of this. In Crotophaga, Eudynamys, and Rhopodytes it barely extends beyond the level of the tibial fibular ridge. The cnemial crests are, as a rule, feebly developed, indeed only in Geococcyx do they attain to any respectable size. In this species the entocnemial crest is more or less quadrate in form; its outer border is convex, its inferior concave. The ectocnemial crest is triangular in form, and terminates in a small pointed process immediately in front of the head of the fibula. The shaft of the tibia is long, slender, and cylindrical, and bowed slightly forwards. I11 Geococcyx the posterior lateral borders of the internal mesotarsal condyle are produced backwards and upwards to form a rather prominent spur. The popliteal fossa of the femur is obsolete. The pelvic limb of the Musophagi is less specialised in some respects than that of the Cuculi. This is especially marked in the character of the tarso-metatarsus. As in the Cuckoos, the hypo-tarsus is complex, and the tarso-metatarsal shaft grooved in front; but the arrangement of the distal trochlese is of a less specialised character, and this fact is especially marked in Schizorhis, the foot of which in this respect closely resembles that of Leptosoma. The foot of Schizorhis, however, may readily be distinguished from that of Leptosoma inasmuch as in the latter the trochlea for D. IV. bears a very strongly-developed outer lip, which is produced inwards towards Me. I. In Schizorhis this trochlea is almost indistinguishable from that of an ordinary eleutherodactyle foot. In Turacus, however, the form of the outer trochlea nearly resembles that of the Cuculi, but is less markedly compressed, and looks backwards and slightly inwards, instead of being twisted so as to cross the shaft transversely. Moreover, it is not raised high up on the shaft as in the Cuckoos. |