502 



THE RABBIT 



(/. vent, r. vent), the mediastinum here fusing with the 

 visceral layer of the pericardium (m. per) and thus ob- 

 literating the space ; below this it again narrows to form the 

 ventral mediastinal space {v. med), in which the thymus 

 (p. 4Qo) is situated. 



In the entire animal, the air-tight pleural cavities are 



ceni 



■t^.jned. 



Fig. 128. — Diagrammatic transverse section of the rabbit's thorax in the region of 

 the ventricles, to show the relations of the pleurae and mediastinum (dotted line), 

 etc. The lungs are contracted. 

 aort. dorsal aorta ; as. v. azygos vein ; cent, centrum of thoracic vertebra ; /. Ing. 

 left lung ; /. pi. left pleural cavity ; /. vent, left ventricle ; nty. spinal cord ; oes. 

 gullet ; par. per. parietal l.iyer of pericardium ; pi. cav. postcaval, close to 

 its entrance into right auricle; r.lng. right lung; r.pl. right pleural cavity; 

 r.vent. right ventricle; st. sternum; vis. per. visceral layer of pericardium; 

 V. med. ventral mediastinal space. (From Parker and Haswell's Zoology.) 



completely filled by the lungs, so that the parietal and vis- 

 ceral layers of the pleurae are practically in contact, there 

 being only a lubricating serous fluid lymph between them. 

 The pressure of the air in the bronchial cavities of the 

 lungs is therefore sufficient to keep them distended ; but as 



