568 ON THE RESPIRATORY ORGANS OF APTERYX. [June 20, 



to those of birds (Crocodilia, Pterosauria, Dinosauvia), pulmonary 

 air-sacs (Chamaeleonidae), and membranous expansions whicli are 

 comparable to the septa in birds. 



In Crocodiles, which approach birds in so many other ways, the 

 resemblance is closest. As in birds, the liver lies between the stomach 

 and the pericardium, and has a peculiar peritoneal investment shut off 

 from the great sac of the abdomen ; and, as in the Ostrich, the whole 

 circumference of the stomach is united by fibrous tissue with the 

 parietes. A fibrous expansion extends from the vertebral column 

 over the anterior face of the stomach, the Uver, and the dorsal and 

 front aspect of the pericardium, to the sternum and the parietes of 

 the thorax, separating the thoraco-abdomiual space into a respira- 

 tory and a cardio-abdominal cavity, and representing the oblique 

 septum of the bird. The respiratory cavity is similarly divided 

 into a right and left chamber by a very deep median septum, 

 traversed from before backwards by the oesophagus, trachea, and 

 pneumogastric nerves, and containing the aortic arches. Each of 

 these chambers is occupied by one of the lungs, the mesial face 

 of which is closely adherent to the septum, while the lateral face, 

 though quite free, naturally fits closely to the parietes. As there 

 are no air-sacs, each chamber has only one story. 



When the lung is distended, its dorsal margin extends far up on the 

 sidesof the bodies and arches of the vertebrae, tbe height of which seems 

 to be related to this dorsal expansion of the lung'. A broad, thin 

 muscle arises, on each side, from the anterior margin of the pubis ; and 

 its fibres pass forwards, diverging as they go, to be inserted into the 

 ventral face of the posterior part of the pericardium andinto the ven- 

 tral and lateral parts of the fibrous capsule of the stomach, passing 

 between that organ and the adherent posterior face of the liver, and 

 being inserted into the fibrous aponeurosis which covers the anterior 

 face of the stomach, and represents the oblique septum. 



Each bronchus is continued directly backwards into a wide canal, 

 which dilates into an oval sac-like cavity at the posterior end of the 

 luDg, representing the mesobronchium with the posterior air-sac in 

 birds. 



In the dorsal and mesial wall of the mesobronchium there are five 

 or six apertures, which lead into as many canals, representing the 

 entobronchia in birds. These pass, the anterior two almost directly 

 forwards, and the others more or less obliquely, to the dorsal margin ; 

 and they lie quite superficially on the mesial face of the lung. The 

 first is very much larger than the others, and ends in a dilatation at the 

 anterior end of the lung. It is united with the second by transverse 

 branches. Along the ventral margin of the lung there are four sac- 

 like chambers, which communicate, in the case of the two anterior, 

 with the entobronchia, and, in the case of the two posterior, with 

 the mesobronchium. Finally, there are two very large canals, external 

 to these, which communicate with the mesobronchium by large aper- 



' It Beems not improbable that the great height of the bodies and arches of 

 the anterior thoracic vertebrae iu some Dinosaurians may be connected with a 

 similar modification of the lungs. 



