254 Transactions. — Zoology. 



General Remarks. 



The study of Notornis suggests certain questions of interest as to 

 flightless birds in general, and especially as to that group of preeminently 

 flightless birds, the Ratitce, and their relations on the one hand to the 

 CarinatcB, and on the other to the reptilian ancestors of the class. 



The Ratitm are usually regarded, from certain undoubted reptilian charac- 

 teristics, as being nearer the reptilian stock from which birds sprang, than 

 the Carinata, and there seems to be a general opinion that large ratite birds 

 of some sort formed the actual connecting link between reptiles of a dino- 

 saurian type and the Garinata. 



But it appears to me that there are serious difficulties in the way of this 

 view. The Eatitce, in many of the most distinctive avian characteristics, 

 approach no nearer to reptiles than do the Carinatce. For instance, in the 

 characters of the vertebra, the femur, the tibio-tarsus, the tarso-metatarsus, 

 the pelvis and sacrum, and, in the case of Dinornis and Apteryx, of the 

 small, backwardly-directed hallux. 



The chief skeletal characters, except those of the skull, in which 

 the RatitcB differ from the Carinata, are : — 



a. The absence of a keel to the sternum : 



b. The great width, and, except in Rhea, the extreme flatness of 



the sternum, i.e. the openness of the transverse sternal angle. 



c. The comparatively small size of the scapula and coracoid. 



d. The coraco-scapular angle is equal to two right-angles. 



e. The axis of the coracoid is vertical or inclined backwards. 

 /. The furcula is rudimentary or absent. 



If the Ratit(B are to be looked upon as in any way an ancestral group, these 

 characters must be considered of primary importance, that is, as having a 

 true phylogenetic significance. But in all these points, the Ratita merely ex- 

 aggerate what we find in the flightless members of the Carinate order. 

 There is no more keel to the sternum in Stringop)s or Cnemiornis than in 

 Struthio, and the transverse sternal angle of Rhea is very considerably less 

 than in the flightless CaiinatcB. In these, also, there is a progressive diminu- 

 tion in size of the coracoid and scapula in passing from good fliers to flightless 

 members of the same class, and at the same time a gradual rotation back- 

 wards of the dorsal end of the coracoid, and increase of the coraco-scaxDular 

 angle. In fact, with the exception of the foramen in the coracoid of the 

 ostrich, I know of no character in the shoulder-girdle of Ratitm which can 

 be pointed out as distinctively reptflian. One important distinction between 

 the shoulder-girdle of reptiles and that of birds, is the position of the bones. 

 In reptiles the coracoid passes from its sternal articulation outwards and 

 slightly upwards, and the scapula (including the supra-scapula), from its 



