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Show 568 ON THE RESPIRATORY ORGANS OF APTERYX. [June 20, to those of birds (Crocodilia, Pterosauria, Dinosauria), pulmonary air-sacs (Chamaeleonidae), and membranous expansions which 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 liver, and the dorsal and front aspect of the pericardium, to the sternum and the parietes of the thorax, separating the thoraco-abdominal space into a respiratory 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 sides of the bodies and arches of the vertebrae, the height of which seems to be related to this dorsal expansion of the lung l. 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 and into the ventral 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 lung, 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 saclike 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- 1 It seems not improbable that the great height of the bodies and arches of the anterior thoracic vertebras in some Dinosaurians may be connected with a similar modification of the lungs. |