568 ON THE RESPIRATORY ORGANS OF APTERYX. [June 20, 
to those of birds (Crocodilia, Pterosauria, Dinosauria), pulmonary 
air-sacs (Chameleonide), 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 respira- 
tory anda 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 osophagus, 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 vertebree, the 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 and into 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 
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 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 seems not improbable that the great height of the bodiesand arches of 
the anterior thoracic vertebre in some Dinosaurians may be connected with a 
similar modification of the lungs. 
