. La structure et la classification des oiseaux . i; 2, 3 flexores perforati et perforantes. Il est absent dans tous les oiseaux qui ont été appelés par himanomalogonatous, ou anormal-kneed. Mais il y a des excuses, à n'importe quel rythme d'un côté. Ainsi, alors que le muscle présent dans les cigognes généralement il est absent des hérons apparentés, et, en effet, est absent dans trois cigognes, Xeno-rhynchus, Abdimia, et Dissura, quand le muscle présente il a en règle générale les relations décrites ci-dessus; butin quelques oiseaux il n'atteint pas au-delà du genou, en montrant, peut-être, une disparition naissante. L'import- STE
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. The structure and classification of birds . i; 2, 3 flexores perforati et perforantes. it is absent in all the birds which were termed by himanomalogonatous, or abnormal-kneed. But there are excep-tions, at any rate on one side. Thus while the muscle ispresent in the storks generally it is absent from the nearlyrelated herons, and, indeed, is absent in three storks, Xeno-rhynchus, Abdimia, and Dissura, When the muscle ispresent it has as a rule the relations described above; butin a few birds it does not reach beyond the knee, thusshowing, perhaps, an incipient disappearance. The import- STEUOTURE AND CLASSIFICATION OF BIKDS ance of this muscle in classification lias been much increasedby Mitchells interesting paper upon its exact relationsto the flexors of the leg in a series of birds. He has shownthat in Balearica chrysopelargus the mass of muscle whichforms the flexor perforatus arises from three distinct heads;one of these is, in common with the flexor longus hallucis, from the intercondylar notch of the femur; the second is. 3zr.2. FLEX. COM. Fig. 53.—Leg Muscles of Opisthocomus (aftee Mitchell).II-IV, -flexores perforati. from the outer condyle of the same bone; the third is fromthe tendon of the ambiens. This tendon divides into three, one for each of the three divisions of the flexor perforatus.The arrangement will be obvious from the accompanyingcut J Apart from slighjj differences in detail the samearrangem.ent was found to hold good for a few other birdsprovided with an ambiens, On the Perforated Flexor Muscles in some Birds, P. Z. S. 1894, p. 495. MUSCLES OF THE HIND LIMB 97 In Nycticorax Gardeni, which has no ambiens, there is adifference in the origin of the flexors in question which is ofgreat interest. The two origins from the femur are as in thecrane. But there being no ambiens there can be no originfrom that muscle. Nevertheless the third head of theflexors is present in the shape (see fig. 53) of a broad ten-dinous band arising from the fibula, w
