14 TOPOGRAPHICAL ANATOMY OF THE 



structures of considerable size intervene between the two mediastinal 

 pleurae, with the result that a more or less extensive mediastinal space 

 is formed. The heart is the largest of these structures, and it is 

 customary to designate that part of the mediastinal pleura that is 

 applied to the membranous sac surrounding this organ by the specific 

 name of 'pericardiac pleura (pleura pericardiaca). 



On following the pleura over the heart — or, more correctly, over the 

 pericardium — it will be discovered that it is reflected over the root of 

 the limg on to the lung itself; that is, the parietal pleura here becomes 

 continuous with the visceral or pulmonary pleura (pleura pulmonalis). 

 It should be further noticed that caudal to the root of the lung the 

 reflection of the mediastinal pleura is carried backwards as far as the 

 diaphragm in the form of the pulmonary ligament (ligamentum 

 pulmonale). 



During the foregoing examination it will have been observed that 

 the mediastinal and costal pleurae meet at the sternum at a very acute 

 angle. Thus the most ventral part of the pleural cavity is very narrow, 

 and is distinguished as the costo-mediastinal sinus (sinus costo- 

 mediastinalis). 



Now trace the costal pleura in a dorsal direction. On reaching the 

 vertebral column the membrane is reflected ventral wards as the 

 mediastinal septum, in which the oesophagus and aorta are conspicuous 

 objects. Again the mediastinal pleurals continuous with the pulmonary 

 pleura by way of the root of the lung and the pulmonary ligament. 



Next investigate the disposition of the pleura at the apex of the 

 chest. Here each sac ends blindly in the cupula ^ pleurce, which, on 

 the left side, generally lies within the first rib, but on the right side 

 may extend beyond the rib and come into contact with the scalenus 

 muscle. 



Finally, the costal pleura should be followed to the diaphragm — 

 where it forms the diaphragmatic pleura (pleura diaphragmatica) — 

 and thence again to the mediastinal septum. 



Owing to the bulging of the diaphragm towards the cavity of the 

 chest, the part of the muscle close to its costal attachment is applied to 

 the inner surface of the ribs. Consequently, in this region — the 

 phrenico-costal sinus (sinus phrenicocostalis) — there is a certain amount 

 of the pleural cavity into which the thin edge of the lung does not 

 extend even during inspiration. Naturally, during expiration and when 

 the hollow abdominal organs are distended, the area of contact of 

 diaphragmatic and costal pleurae is greater. 



The diaphragmatic line of pleural reflection, that is, the line along 

 1 Cupula [L.], a cup, dim. of cupa, a tub. 



