1882. ] ORGANS OF APTERYX. 563 
mesenteric arteries, which thus appear in the middle line of the 
oblique septum when this is viewed from below and behind. The 
vena cava inferior enters the pericardium just behind the attach- 
ment of the oblique septum to it. 
Immediately after the bronchus has entered the lung, it enlarges 
somewhat to form a dilatation, which has been termed the vestibule. 
A trunk which continues the: direction of the bronchus through 
the centre of the parenchyma of the lung backwards, leaves the 
posterior end of the vestibule, and ends at the superior end of 
the posterior ventral margin in the posterior ostium, by which it 
opens into the posterior air-sac. This trunk may be termed the 
mesobronchium, by way of distinction from certain others which have 
a superficial position on either the lateral or the mesial face of the 
lung; and which may be distinguished, respectively, as ecto- and 
ento-bronchia. 
Toward the middle of its course the mesobronchium gives off a wide 
branch, which passes backwards and downwards to the posterior 
ventral edge of the lung, and opens there by a very wide posterior 
intermediate ostium into the corresponding air-sac. 
The entobronchia (“ bronches diaphragmatiques,’’ Sappey) are four 
in number. They take their origin in wide openings of the dorsal 
wall of the vestibule. The fourth is hindermost, runs almost directly 
backwards to the posterior end of the lung, and ends there cecally. 
Branches are given off only from its ventral wall. 
The third entobronchium runs parallel with this, giving off a 
number of close-set branches from its dorsal side, which are distri- 
buted over the superior facet. Close to the entrance of the bronchus, 
this presents the large anterior intermediate ostium for the corre- 
sponding air-sac. 
The second entobronchium passes directly dorsad, and ramifies 
over the middle of the superior facet. A wide branch descends to 
the subbronchial ostium. 
The first entobronchium curves sharply round the entrance of the 
bronchus, and from its anterior or convex wall gives off a number of 
branches to the anterior part of the superior facet and to the anterior 
inferior facet. One of these branches passes directly forwards, and 
opens by the prebronchial ostium into the prebronchial air-sac ; 
while the inferior end of the trunk opens below the bronchus, into 
the subbronchial ostium, and, in that way, communicates with the 
subbronchial air-sac. 
Thus the mesobronchium and the first entobronchium are each 
connected with two air-sacs—the former with the posterior two, and 
the latter with the anterior two ; while the middle air-sac (anterior 
intermediate) communicates with the third entobronchium so close 
to the vestibule that it might almost be said to open into the latter. 
Behind the vestibule, the mesobronchium gives off successively 
several (usually six or seven) branches, which are directed laterally 
and dorsally towards the lateral or costal face of the lung. These 
are the ectobronchia (“ bronches costales,”’ Sappey). 
Those parts of the walls of the various bronchia and their ramifica- 
