OCR Text |
Show 910 DR. R. W. SHUFELDT ON THE OSTEOLOGY OF THE [Dec. 1, their composition goes, are more generally known, and the characters they present have been enlisted by ornithologists from time immemorial to serve the purposes of classification. Thanks to this being the case, references to the member in the present instance can be made much briefer than in the case with the pectoral limb, and still fully meet our purpose. In Whippoorwills and Night-hawks the bones of this extremity are always non-pneumatic, and, with the exception of rather a short tarso-metatarsus, harmoniously proportioned as to lengths and calibre. Chordediles possesses nearly a straight shaft to its femur, which is smooth, and quite cylindrical. The trochanterian ridge does not rise above the articular summit of the bone, and of the condyles at its distal extremity the external one is the lower. A patella seems to be wanting in these birds, its place being filled by a bit of cartilage in the tendon. The shaft of tibio-tarsus is likewise straight and subcylindrical; the chief point of interest in this bone, however, is the complete suppression of the ectocnemial ridge, while the procnemial one seems to have moved to a more central position on the shaft. A not very strong fibula fails to anchylose with this latter below, and makes unusually weak connections with it above. Tarso-metatarsus has a subcubical hypotarsus, apparently un-pierced by the flexor tendons ; otherwise this segment presents nothing worthy of special record. A well-developed accessory metatarsal is attached in the usual way, rather high on the shaft, by ligament. The formula for the podal digits, being 2, 3, 4, 4, is well known and requires no particular mention. In the delicate pelvic limb of Trochilus we also find a non-pneumatic femur with straight and cylindrical shaft, and with the characters of the extremities much as in the Goatsuckers. Humming-birds, however, have a large, free patella developed, of the most usual form. In them the fibula remains independent of the main leg-bone, but is notably short and puny. Tibio-tarsus has nearly a straight shaft, and carries the peculiarity seen in Chordediles one point further, in having both the cnemial ridges so feebly pronounced as hardly to be noticed, unless specially searched for, when only faintest traces of the procnemial ridge become evident. The usual osseous bridge confines the extensor tendons at the distal end of this bone. The hypotarsus of the tarso-metatarsus is both pierced and grooved for the transmission of the flexor tendons, and the free accessory metatarsal is suspended high upon its shaft. In number and arrangement the joints of the digits of pes agree with the formula of the typical Passerine foot, and are here most noted for the unusual lengths of the ungual phalanges when compared with the basal and remaining joints. While the pelvic limb in the Swallows seems to be constructed after the true Passerine type, in the Swifts it makes a marked departure from this, presenting at the same time a number of points of no little interest. |