^S85.J VISCERAL ANATOMY OF BIRDS. 837 



down the barriers between the Ratitse and the Carinatse in the first of 

 these two directions, I may briefly review our knowledge npou the 

 subject. 



In his classical paper upon the ' Classification of Birds ' ' Prof. 

 Huxley defined the Ratitse, and pointed out the differences which 

 separate them from tlie Carinatee. Although that paper was only 

 published in the year 1867, it is interesting to note how the progress 

 of research has broken down so many of the barriers which at that 

 time were supposed to separate the Ratitte from the CarinatEe. 



The peculiarities of the skull I need not refer to, since they are 

 repeated in the Tinamons, which in so many other respects resemble 

 the Grallinaceous birds, and therefore form an annectent group between 

 the Ostrich-tribe and the other Carinatae. 



The shoulder-girdle has been held to be characteristic and to form 

 a well-marked distinction between the Ratita^ and the CarinatEe; but 

 anatomists are now agreed that the sternum, at least, is not so charac- 

 teristic as it was at one time believed to be. In the first place the 

 presence of a " keel " is invariably associated with the power of 

 flight, or, to speak more accurately", with a great development of the 

 pectoral muscles ; thus we find a keel on die sternum of the Bat, 

 Mole, and P;;erodactyles, while it is absent in Striyops, the flightless' 

 parrot of New Zealand, and in Cnemiornu\ 



Moreover, Prof. Jeffery Parker, in a paper upon the Osteology of 

 the New Zealand Rails =*, has given reasons for believing that' the 

 angle between the scapula and the coracoid becomes less and less as 

 the power of flight is diminished, so that this supposed peculiarity in 

 the shoulder-girdle of the Struthiones is merely correlated with" the 

 loss of the power of flight. 



It is commonly stated that the Struthiones possess no lower 

 larynx, and this assertion is repeated from text-book to text-book 

 in spite of the fact that my predecessor, the late Mr. W. A. Forbes, 

 has conclusively shown ' that certain of the Struthiones, il' not the 

 whole group, possess a syrinx which is essentially comparable to the 

 syrinx of the Carinatae, and, in the case of Rhea, is absolutely indistin- 

 guishable from a Carinate syrinx. 



Certain of the statements of Sir Richard Owen respectino- the 

 anatomy of Apteryx have been since controverted. Prof. H^iixley 

 has shown that the respiratory organs of this bird, though certainly 

 dift'ering in detail, present no essential modifications from the respi"- 

 ratory organs of other birds ; there is no structure unrepresented 

 in other birds present ; the supposed "diapliragm" is in reality not 

 comparable to the diaphragm of the mammalia ; and even if it "were, 

 it has its exact homologue in the Carinatae. Prof. Lankester = and 

 I « have shown that the heart of Apteryx is precisely like that of 

 any other bird. 



The presence of two nails upon the hand of Struthio, to which 

 Prof. Huxley has called attention, is no doubt, so far. an archaic 



1 P. Z. S. 1867. p. 415. 4 Collected Papers, p. 232 



See P. Z S^ 1873. p. 7fi3. . P. Z. S. 188.^ p. 415 " 



Trans. >.-Z. Inst. vol. xiv. p. 245. ^ P. Z. S. 1885, pp. 188, 477. 



