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Show 1899.] OSTEOLOGY OF T H E PYGOPODES. 1037 foramen is shut off from the fissure by a bar of bone. The pubis is long and rod-shaped throughout in the Podicipides, but becomes spatulate at its free end iu the Colymbi. There is no pectineal process. The preacetabular ilium, the ischium, and pubis become more or less completely ossified at a much earlier date than the postacetabular ilium. This last is as yet for the most part still cartilaginous. The separate elements of the innominate bones are still very distinct. viii. T H E P E C T O R A L LIMB. The wings of the Grebe and Diver bear a very close similarity, and perhaps more nearly resemble those of Phalacrocorax than of any other group. The wing of the Diver can be readily distinguished from that of the Grebe by the great relative length of the metacarpals. As Shufeldt (18) has pointed out, the Divers in this particular probably stand alone. The delto-pectoral crest is larger in the Diver, and the fossa for the brachialis internus is deeper. There is no ectepicondylar process nor subtrochanteric pneumatic fossa. The delto-pectoral crest in the Divers is separated from the crista inferior by a deep gorge-the planum intertuberculare ; this in the Grebe is represented only by a shallow depression. The coraco-humeral groove takes the form of a deep pit ventrad and distad of the caput humeri. The forearm iu the Grebe is nearly as long as the arm, considerably less so in the Divers. In the manus the great length of the metacarpals in the Colymbi has already been commented on; the 1st phalanx of digit II. in the Divers is relatively shorter and broader than in the Grebes ; the same applies to the remaining phalanges. The carpus does not seem to call for any special remark. For further details concerning the fore limb, see Key (p. 1041). ix. THE PELVIC LIMB. The pelvic limbs of the Grebe and Diver bear an exceedingly close resemblance one to another, but differ in almost every particular from those of any other group. The femur is very short and thick, with a strong dorsal curve. Its proximal and distal extremities are greatly elongated transversely. The head lies rather below the level of the antetrochanter, and bears a deep fossa for the ligamentum teres. The fibular condyle is of great size, and lies considerably below the level of the tibial. The tibio-tarsus is remarkable for the enormous development of the cnemial crests, which form a large pyramidal process projecting vertically upwards beyond the femoral articular surface. This PROC. ZOOL. Soc-1899, No. LXVII. 67 |
