1882. ] ORGANS OF APTERYX. 561 
ends of the vertebral ribs. The lowest point of the ventral margin 
lies on one of these ribs, not far from its articulation with the sternal 
rib; and the hinder part of this margin, or the posterior ventral 
margin, slopes upwards and backwards, while the anterior ventral 
margin is inclined upwards and forwards from this point, which may 
be called the ventral angle of the lung. The whole ventral margin 
of the lung is very thin; its dorsal margin, on the other hand, is 
thick and rounded off into the outer or lateral face of the lung, which 
is convex from above downwards. The dorsal margin and the 
lateral face are closely applied to the parietes ; and the former presents 
deep notches, into which the necks and dorsal portions of the bodies 
of the ribs are received. 
The mesial face of the lung is divisible into three facets :—a 
superior, which is closely applied to the lateral faces of the vertebree 
and to a fibrous lamella, the median vertical septum, which proceeds 
from the ventral faces of the vertebree in the middle line; and an 
anterior inferior and a posterior inferior facet, which occupy 
that slightly concave face of the lung which is turned towards the 
thoracic cavity. These last facets are divided by a ridge or eleva- 
tion of the surface of the lung, which ascends from the ventral angle 
to the insertion of the bronchus. This is always situated at some 
considerable distance from the anterior end of the lung. 
The anterior inferior and posterior inferior facets of the lung are 
closely invested by a thin fibrous membrane, which may be termed 
the pulmonary aponeurosis (‘‘diaphragme pulmonaire,” Sappey ; 
‘ diaphragmite antérieur,” Milne-Edwards). The mesial edge of this 
is continuvus with the median vertical septum; the lateral edge is 
inserted into the parietes of the thorax immediately beyond the 
ventral edge of the lung. Around the pneumatic apertures, or ostia, 
the pulmonary aponeurosis is closely adherent to their margins ; 
it is, in fact, perforated by them. 
Broad flat bands of striated muscle (the costo-pulmonary muscles) 
take their origin from the vertebral ribs’, at some distance below 
the attachment of the pulmonary aponeurosis, and, proceeding 
obliquely dorsad and forwards, spread out and are inserted into 
that part of the aponeurosis which covers the posterior inferior facet. 
They are supplied with branches of the intercostal nerves. This 
pulmonary aponeurosis with its muscles is one of the two structures 
which have been compared to the mammalian diaphragm. 
The second so-called “diaphragm” (‘ diaphragme thoraco-ab- 
dominal,” Sappey; ‘‘diaphragmite thoraco-abdominal,”’ Milne- 
Edwards) is a more or less aponeurotic fibrous membrane, continuous 
with the ventral edge of the median dorsal septum and suspended 
by it, like the roof of a tent, across the thoraco-abdominal cavity. 
In the middle line, this odliqgue septum slopes downwards and for- 
wards to the dorsal and anterior face of the pericardium, with which its 
fibres become firmly connected on their way to their attachment to 
1 In many birds there are additional “ sterno-pulmonary” muscles, which 
proceed from the antero-lateral part of the sternum to the aponeurosis covering 
the anterior inferior facet. 
