PHYLOGENY OF THE PAIuEOGNATILffi AND NEOGNATH^. 253 



the oesophagus for a considerable distance beyond the level of the 1st cervico- 

 thoracic rib. 



The sub-bronchial sac is divided into right and left loculi, enclosing a median 

 tunnel-like space between them, the roof of which is formed by the trachea. This 

 tunnel can be traced into a large pneumatic cavity in the sternum opening on its 

 anterior border in the middle line between the coracoid grooves. 



The intermediate sacs were three in number. A similar subdivision has been de- 

 scribed by Beddard in Podargus and " one or two Accipitres." In the present instance 

 it would seem that this third sac is due to a subdivision of the anterior intermediate. 



The posterior intermediate was large. Its roof was pressed inwards by the forward 

 extension of the posterior abdominal. 



The posterior abdominal was of considerable size. That of the right side enclosed 

 the right kidney ; on the left side the anterior lobe of the kidney was found to lie 

 without the sac and to be enclosed in a separate sac. 



The intermediate and posterior abdominal sacs of the right side were markedly 

 smaller than those of the left. 



The sacs are fed as follows : — The pre-bronchial and sub-bronchial by a common 

 ostium from ento-bronchium i. ; the anterior intermediate (a) from ento-bronchium in., 

 and (b) from the anterior of two canals arising one immediately behind the other from 

 the ventral floor of the meso-bronchium immediately below the apertures of the 

 iii.-iv. ecto-bronchia. The ento-bronchial ostium opens into the anterior, the 

 ecto-bronchial into the posterior loculus. The posterior intermediate by the hinder 

 of the two hinder ecto-bronchial canals. The posterior abdominal by the terminal 

 end of the meso-bronchium — the ostium posterius. 



The 2nd ento-bronchium does not open, as described by Huxley in Apteryx, into 

 the sub-bronchial ostium, but turns upwards and backwards, and terminates caecally 

 like the 4th. 



The air-sacs in Rhea differ in no essential respect from those of Casuarius. 

 The sub-bronchial sac is unpaired. In one Rhea americana which I dissected the 

 anterior intermediate sac was fed by two ostia widely separated one from another. In 

 a second example the ostium of the anterior intermediate sac of the left side and the 

 septum dividing this sac from the posterior intermediate were both wanting. 

 The posterior abdominal sacs are much larger than those of the Cassowary. 

 Apteryx differs from all other birds, as was first pointed out by Huxley, in that, 

 owing to their smaller size, the posterior intermediate and abdominal sacs are enclosed 

 within the sub-pulmonary chamber. In all other birds a great increase in the size of 

 these two has driven out the posterior abdominal sac, so that it projects, like a 

 hernial sac, between the peritoneum and the parietes into the abdominal cavity. 



The respiratory organs of the Palceognathce are singularly uniform in character 

 inter se and with the Neognathce. 



vol. xv. — part v. No. 19. — December, 1900. 2n 



