Figure 2
The Post Pulmonary Septum in Testudo Overview of the coelomic subdivision and the resulting compartmentalization of the respiratory system in tortoises. The left image shows in a ventral view the viscera, except for the lungs, have been removed. The schematic drawing on the right indicates the structures in question. Unlike in most other clades of chelonians, the ventral side of the lungs is completely covered by the postpulmonary septum (PPS). The anatomically left side shows the medial parts of the PPS removed, giving a clear view on the actual lungs beneath (i.e. dorsal to) it. Dorsally, the lungs are broadly fused to the inner side of the carapace (indicated by the wavy lines), resulting in a firm fixation within the pleural cavity. Note the PPS extending laterad to the carapace. The anatomical configuration serves as a mechanical support system in inverted tortoises whose viscera are pushing on the lungs. As a consequence, the PPS prevents gravitational pulmonary collapse in inverted specimens and hence counteracts the resulting decrease in compliance together with the associated increase in work of breathing. Photograph taken by ML.
