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Show 1890.] ANATOMY OF PODICA SENEGALENSIS. 441 to one organ or system, but are manifested in the entire structure- bones, muscles, and viscera. It appears to m e, therefore, to be necessary to strongly emphasize the justice of regarding the Heliornithidce as a distinct and well-marked family. The following is a brief definition of that family :- Characters of the Family Heliornithidae. Schizognathous holorhinal birds with 18 rectrices, moderately long caeca, a tufted oil-gland, no aftershaft; with an elongated one-notched sternum and low carina; clavicles with an anterior and posterior interclavicular process, the latter firmly attached to the carina sterni; the skull without basipterygoid processes, occipital foramina and supraorbital furrows, and without greatly developed temporal fossae. Biceps slip ending freely on patagial membrane: expansor secundariorum well developed; in the hind limb ambiens, femoro-caudal, accessory femoro-caudal, semitendinosus present, accessory semitendinosus absent; relations of biceps cruris peculiar. Muscular formula of leg A B X + . Affinities of the Heliornithidae. It is curious to notice that the osteological characters and those shown by the muscles are almost in antagonism. Judged entirely by its myology, Podica would be referred to the Pygopodes, though it would doubtless be regarded as an aberrant member of that group \ If only osteology were taken into consideration, then Podica would be as unhesitatingly assigned to the Rails, though the characters afforded by the sternum would necessitate its separation as a very distinct genus from the other Rail-like birds. Which set of characters are w e to be guided by in attempting to settle the systematic position of the Heliornithidce ? It is hardly necessary to emphasize the fact that in deducing affinities one character is not as good as another; adaptive characters must clearly be set aside when they are not in harmony with structural characters showing no evident relation to the mode of life of the bird. I should be inclined therefore, in the first place, to discount very liberally the skull characters, as least some of them. The strongly developed temporal fossae with the ridges on either side of them distinguish the Grebes from the Rallidce. But w e find exactly the same extraordinarily developed fossae in the Ardeidce and in Plotus and Phalacrocorax. These birds, like the Grebes, use their neck and heads greatly and have powerful muscles which are inserted 1 This makes m e think that Mr. Forbes must have dissected Podica or Podoa; otherwise, if he had only published accounts to go upon, or had only examined the osteological structure, he would hardly have definitely placed it in the same group with the Divers and Grebes, as he did at the close of his career [12]. |
