1882.] ORGANS OF APTERYX. 567 
with the vertebral column above, and the cesophagus and bronchus 
below. Laterally, it is bounded by so much of the anterior facet of 
the lung as lies above the level of the bronchus. Mesially, it is 
widely separated from its fellow by the fibrous tissue continued from 
the anterior end of the median vertical septum onto the cesophagus, 
bronchi, and aorta. 
The prebronchial air-sac in the Duck is fully three times as long, 
and sends off prolongations to the vertebral column, which have been 
described by Sappey. 
8. The vestibule, mesobronchium, and entobronchia of Apteryx 
present no important differences from those of the Duck, except 
that the branches of the entobronchia are less numerous. 
The ectobronchia, on the other hand, are much smaller, and only 
the most anterior reaches the lateral surface of the lung, and there 
divides into an ascending and a descending superficial branch of 
small size ; the others break up into parabronchia before reaching the 
surface of the lung. 
9. The parabronchia are much wider in Apteryx, the diameters 
of their cavities varying from 1°5 millim. to 0°8 millim., while they 
range from 0°8 to 0:4 millim. in the Duck Moreover the inter- 
vening vascular parenchyma is relatively much narrower in Apteryx 
than in the Duck. Hence a section of the lung of the former 
appears much more coarsely spongy than one of the latter. In the 
Duck, as in many other Carinate birds, the parenchyma around each 
parabronchial canal is defined by linear interspaces from that of ad- 
jacent parabronchia; and in transverse section these boundaries have 
a polygonal, usually hexagonal form. In Apteryz, the parenchyma 
between the parabronchial tubes is continuous, and the interca- 
pillary air-passages show no interruption. 
In the Duck, as in most Carinatee, the fossulze lead into branching 
passages (intercellular passages of Rainey), which radiate towards the 
periphery of the area of parenchyma which belongs to each para- 
bronchium, finally ending in the intercapillary passages. In Apteryz, 
the fossulze are mere shallow pits which open at once into the inter- 
capillary passages. 
Thus the respiratory organs of Apteryx are thoroughly ornithic, 
differing from those of other birds chiefly in the greater width and 
smaller aggregate surface of the respiratory passages, in the rudi- 
mentary condition of the pneumatic sacs, and in the much greater 
strength of the pulmonary and septal aponeurotic expansions. 
Neither in Apteryx, nor in any other bird, has either of these the 
slightest real resemblance to a Mammalian diaphragm. Jor, as has 
- been seen, the heart lies altogether behind both, and the muscular 
digitations of the pulmonary aponeurosis are supplied by the inter- 
costal nerves, the phrenic being absent. The vertical and oblique 
septa really answer to the fibrous tissue of the posterior and middle 
mediastinum in Mammals. 
In this, as in all other cases, the meaning of ornithic peculiarities 
of structure is to be sought, not in Mammals, but in Reptiles. It 
is only among Reptiles that we meet with pneumatic bones similar 
Proc. Zoou. Soc.—1882, No. XX XVIII. 38 
