2 6 NEORNITHES RATITAE chap. 



descendants of the Archaeornithes-, as each may be a separate 

 offshoot from the same parent stem. All we can safely assert is, 

 that the former were in existence about the end of the Jurassic 

 times, that teeth were still retained in some cases during the 

 Cretaceous Epoch, and that not only normal forms, but also flight- 

 less forms without keel or pygostyle,^ had arisen hj that date. 



(A) The Ratitae are commonly characterised as Birds with no 

 keel to the sternum ; but this will not hold as a definition, since 

 Hcsperornis has also that peculiarity, while such genera as Didvs, 

 Stringops, Cnemiornis, and Notornis are nearly in the same con- 

 dition. It is no one point, therefore, but the sum of many, which 

 enables us to draw so clear a line of demarcation between this 

 primitive group and the remainder of existing forms ; neverthe- 

 less it is convenient to preserve the name unaltered, as it is well 

 understood to what members of the class it is more especially 

 meant to apply. The rhamphotheca, or horny sheath of the bill, 

 instead of being simple, is composed of several more or less separate 

 pieces, as in the Procellariidae, Tinamidae, and Steganopodes ; the 

 quadrate bone, by means of which the lower jaw is articulated to 

 the skull, in place of two proximal knobs has only one, as in 

 Hesperornis, Ichthyornis, and the Tinamidae ; the coracoid and 

 scapula are fused together, and meet at an obtuse, as opposed 

 to an acute or right, angle ; and the last six or seven caudal 

 vertebrae do not coalesce into a pygostyle, or upright triangular 

 expansion to carry the rectrices, a state of things found else- 

 where in Hesperornis and the Tinamidae.' The reduced wings 

 preclude flight ; the tail is functionless, as in the Podicipedidae 

 and Tinamidae ; the tongue is very small ; the oil gland is 

 absent ; the penis is large and erectile, being comparable to that of 

 the Anseriformes ; while in the adult the feathers are evenly dis- 

 tributed over the whole surface, as in the Spheniscidae and Pala- 

 medeidae, no down being present. Claws are found on the pollex 

 and index in Struthio and Ehea, or occasionally on the third digit ; 

 in Casuarius, Dromaeus, and Apteryx they occur only on the index. 



Eatite Birds proper are comprised in six groups, Struthiones 

 or Ostriches, PiHEAe or Nandus, Megistanes or Cassowaries and 

 Emeus, Apteryges or Kiwis, Dinornithes or Moas, and Aepyor- 

 NITHES or Eocs. 



' H. Gadow, Bronn's, Thier-Reieh, Avcs, Syst. Theil. 1893, p. 90. 

 - A pygostjde is occasionally found in StriUhio and Airieryx. 



