562 PROF, HUXLEY ON THE RESPIRATORY [June 20, 
the sternum. From the median line, the two halves of the oblique 
septum slope laterally and ventrally until they attach themselves to 
the parietes of the abdomen behind, to those of the thorax more 
anteriorly, and to the margins of the sternum in front, at a con- 
siderable distance from the attachment of the pulmonary aponeurosis. 
It follows that a wide interspace is left, on each side, between the 
pulmonary aponeurosis, dorsally and laterally, the dorsal median 
septum in the middle line, the oblique septum ventrally and below, 
and the parietes of the body laterally ; and, as the mesial attachments 
of the pulmonary aponeurosis and of the oblique septum are very 
much closer together than their outer attachments, the whole cavity 
has somewhat the form of a wedge with the narrow edge towards 
the middle line. This swbpulmonary chamber is divided into four 
loculi by three dissepiments, which pass transversely from the lateral 
face of the oblique septum to the mesial face of the pulmonary 
aponeurosis. Each loculus lodges one of four postbronchial sac- 
cular diverticula of the wall of the lung, constituting the proper 
air-sacs, which thus fill up the subpulmonary chamber, between the 
insertion of the bronchus and its posterior extremity. Another air- 
sac lies in front of the insertion of the bronchus, on the mesial side of 
the anterior extremity of the lung. 
Thus, on each side, there are five air-sacs, the lateral and superior 
face of each of which abuts against a particular region of the lung. 
The most anterior is that just mentioned, which may be called pre- 
bronchial (“ réservoir cervical,’ Sappey), as the bronchus lies between 
it and the next, or subbronchial (‘‘ interclavicular,”’ Sappey). The 
dissepiment which separates the loculus of this sac from the next is 
attached mesially along the oblique elevation which runs from the 
insertion of the bronchus to the ventral margin of the lung. The 
following dissepiment is attached dorsally, near the origin of the 
cceliac artery from the aorta, which lies in the median dorsal septum, 
and thence to the pulmonary aponeurosis, along a line which is in- 
clined more or less obliquely backwards, to the posterior ventral 
margin. It separates two loculi, which lodge the anterior and the 
posterior intermediate air-sacs (“ réservoir diaphragmatique antérieur 
et postérieur,” Sappey). The third dissepiment, still more inclined, 
divides the loculus of the posterior intermediate air-sac from that of 
the posterior air-sac (“‘réservoir abdominal,” Sappey). 
Thus, that part of the thoraco-abdominal cavity which lies dorsad 
and anterior to the oblique septum lodges no other viscera than the 
lungs and the air-sacs, and may therefore be distinguished, as the 
respiratory cavity, from the cardio-abdominal cavity, which contains 
the heart and the rest of the viscera, and lies below and behind the 
oblique septum. The respiratory cavity is further divided into two 
lateral chambers by the median dorsal septum; and each of these 
chambers is subdivided by the pulmonary aponeurosis into two 
stories, of which the upper is occupied by the lung, and the lower 
by the loculi with their contained air-sacs. 
The dorsal aorta traverses the median dorsal septum from before 
backwards, giving off, from its ventral aspect, the coeliac and the 
