562 PROF. HUXLEY OX THE RESPIRATORY [Juiie 20, 



the sternum. From the median Une, the two halves of the obhque 

 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 

 jjulmoiiary 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 subindmonary 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, wliich 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 prce- 

 bronchial (" reservoir 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 i;i the median dorsal septum, 

 and thence to the pulmonary aponeurosis, along a line which is in- 

 clined more or less obhquely backwards, to the posterior ventral 

 margin. It separates two loculi, Avhich lodge the anterior and the 

 posterior intennediate air-sacs (" reservoir diaphragmatique anterieur 

 et posterieur,'" Sappey). The third dissepiment, still more inclined, 

 divides the loculus of the posterior intermediate air- sac from that of 

 i\iQ posterior air-sac ("reservoir 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 

 luno-s 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 

 chauibers is subdivided by the pulmonary ajjoneurosis 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 coehae and the 



