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Show 1885.] TROCHILID.E, CAPKIMULGIDiE, AND CYPSELIDiE. 911 Returning to our White-throated Rock-Swift, I find that the proximal end of Its femur is so broad in its transverse diameter as to obliterate the neck, making the head of this bone more than usually sessile with the shaft. The trochanterian ridge does not rear above the plane of the summit; in fact, the top of the bone is entirely level. Its shaft is cylindrical only at its middle, from which point it gradually enlarges in the direction of the extremities. The intercondyloid fossa is shallower than is commonly the case, and the prominences themselves not so sharply defined as they often are in other birds. This Swift does not possess a patella, as we found to be the case in Trochilus. So poorly developed is the fibula that in the specimens before me I fail to find an instance where it is produced beyond the fibular ridge on the side of the shaft of the tibio-tarsus. Above this, however, its condition is somewhat better, and it meets the femur in the usual notch of the outer condyle. Tibio-tarsus differs very considerably from this bone as it occurs in the vast majority of the class. The outline of its proximal extremity is nearly square, and the undulating articular surface it encloses gradually slopes from the inner to the fibular side. There is no trace whatever of the pro- and ectocnemial ridges on the anterior aspect, where they occur in most birds. The shaft is straight though slightly compressed in the anteroposterior direction. As we approach its distal end, it becomes curiously twisted, giving the condyles a peculiar cant not easy to describe. The inner condyle is fully as prominent behind as it is in front (rare), while the intercondyloid notch is of equal depth all the way round. The bony bridge for the extensor tendons is present and situated low down, while on the inner and anterior border, higher up on the shaft than common, is seen a strong tubercle for ligamentous attachment, a ligament which we know fulfils a similar purpose. The tarso-metatarsus is comparatively short, and it, too, is quaintly fashioned. Its hypo-tarsus is perforated by one large and open groove, which absorbs its entire central portion, to the very base of this process, being continued down the shaft behind as a shallow excavation. Anteriorly, the shaft is longitudinally and still more decidedly grooved, being pierced above by a foramen that passes directly through the bone. The usual foramen occurs at the distal extremity for the passage of the artery. The anterior faces of the three trochlear are about in the same plane in front, while posteriorly they develop prominent processes for the attachment of strong ligaments, which confine the plantar tendons as they pass to the toes. Of these three trochlear projections the innermost one is tbe lowest, the middle one rather higher, and the outermost one the highest of all. This Swift forms no exception to the well-known rule which 59* |