ELEMENTARY SKETCH OF THE OSTEOLOGY OF BIRDS. 25 



here, therefore, a transition from the mammalian limb through 

 the crocodilian and dinosaurian to the avian limb, which confirms 

 the very close relationship which we have already found to exist 

 between the osseous systems of birds and reptiles.* 



There now only remains the foot of the bird ; the compo- 

 nent digits and phalanges of which are shown in the figured 

 skeleton, I., II., III., IV. As we have already seen, the fifth 

 toe is never developed, and the normal number of the phalanges 

 in the digits of the bird is (as in many reptiles), 2, 3, 4, 5, rec- 

 koning from the first to the fourth digit. Usually the first 

 digit is directed backwards, and the other three forwards. In the 

 Owls, the fourth digit can also be directed backwards at will, and 

 in the Parrots, Toucans, Cuckoos, Woodpeckers, and other climb- 

 ing birds this, as well as the first digit is directed permanently 

 backwards. In the Trogons, the first and second digits are 

 directed backwards ; while in the Swifts and some other birds 

 all the four digits are directed forwards. 



Classification. — In concluding this sketch I have appended 

 two of the modern schemes proposed for the classification of 

 birds. The first of these, with the exception of the first great 

 division, to which is appended the name of Professor Marsh, 

 is the arrangement put forth by Professor Huxley, in his paper 

 on the classification of birds which we have already referred to. 

 The second arrangement, which difiers from Professor Huxley's, 

 only in respect to part of the Carinatse, is that put forward re- 

 cently by Professor Newton, in the article " Birds" in the 

 *' Encyclopaedia Britannica." 



AV.ES. 

 /. — The jaws furnished with teeth. 

 I. Odontorn^. (Marsh.) 



a. Vertebrse biconcave. 



1. Icthyornidce. (Icthyornis.) f 



2. Apatornid(S. (Apatornis.) 



b. Vertebrge normal. 



3. Hesperornidse. (Hesperornis, Lestornis.) 



4. Odontopterygidse. (Odontopteryx.) 

 II. — Jaws without teeth. 



A. Metacarpals not anchylosed together ; tail longer than body, 



*, '..T""!*^ refer the reader to Professor Huxley's " Anatomy of Vertebrated Ani- 

 mals, tor turther details respecting the similarities between the skeletons of birds 

 and reptiles. 



t It is not impossible that these birds with biconcave vertebra should be put 

 be U8*e d^^*'^''*^ ^i^ision of the first class ; for which the name Icthyosgondylia might 



