502 tup; rabbit chap. 



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

 visceral layer of the pericardium {vis. per) and thus ob- 

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

 ventral mediastinal space (7'. nied), in which the thymus 

 (p. 4go) is situated. 



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



cent 



par.per 



Kl(,. ij8. — Diagraniin.ilii. tralis\'ei\se suction of ihe laljbit's thorax in the legion of 

 the N'entricieh, to show the relations of the ptema; and mediastinum (dotted line), 

 etc. The lungs ale L<>ntracted. 

 aoi-t. dorsal aorta ; n^. -'. a/ygos vein ; icitt. centrum of thoracic vertebra ; /. tng. 

 left lung ; /. //. left pleural cavity- ; /. z'fui. left veutiicle ; my. spinal cord ; ocs. 

 gullet ; par. />ur. ]>arietal layer of pericardium ; pt. caz'. postcaval, close to 

 its entrance into right ain-icle ; r. big. right limg ; r. pi. right pleural caA ity : 

 r.voit. right ventricle: .*/. sternum; "'is. per. visceral layer of pericardium; 

 "'.)iicd. ventral mediastinal space. (Fioni Parker and \{;\^\\^i\W /.oology.) 



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

 ceral layers of the pleura; 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 therelore sufficient to keep them distended ; but as 



