Characteristics of the Vertebrata. Iv 



of Chelonia and Ophidia, provided with a hard knob on their upper 

 mandible, for breaking- thi-ough their shell when ready for hatching'. 

 In some Birds the food-yolk is large, and the yoimg are ordinarily 

 more or less entirely competent to provide for themselves when 

 hatched. Where the yolk is relatively small, the young are in- 

 competent to locomotion when hatched, and require to be brooded 

 upon whilst going through further stages of development. Birds 

 which are possessed, immediately after hatching, of the faculty of 

 self-help have been called ' Autophagi,^ in opposition to those which 

 require further maternal care, and are called ' Insessores/ 



Existing Birds are divided into two orders, the Hatitae^ in which 

 the sternum has no crest and the wings are rudimentary, and 

 the Carinatae, in which the sternum has a crest or keel, ossi- 

 fied from an indejaendent median azygos centre, and which have 

 powerful anterior limbs ordinarily organized for flight, though 

 sometimes not, as in the Penguins. The former order includes only 

 the genera Strnthio, Bromaeus, Casuar'ms, Apteryx, and is distin- 

 guished not only by many modifications cm'tailed by the stunting 

 of their anterior limbs, but also by many morphological points of 

 affinity to the cold-blooded Sauropsida, amongst which the cha- 

 racters of the osseous system are peculiarly striking. The Ratiiae 

 have the barbs of their feathers disconnected, have no inferior 

 larynx, and no angle at the junction of coracoid and scapula. A 

 more perfect diaphragm exists in them than in the Carinatae. 

 This latter order comprises all other existing Birds. The fossil 

 Archaeoptenjx appears to have differed from existing Birds by 

 possessing a series of caudal vertebrae equalling the body in length, 

 and in having well- developed non-anchylosed metacarpals. A sepa- 

 rate order, that of Saururae, has been established for the reception 

 of this transitional form. 



Class, Reptilia. 



Air-breathing cold-blooded Vertebrata, with epidermal struc- 

 tures of the character of scales, into which processes of the cutis 

 vera are prolonged, but which are not developed like feathers within 

 saccular involutions of the integument. Accordingly as bony 

 scutes are combined with these scales, and constitute an osseous 

 dermal skeleton or not, existing lleptiles are divided into the 



