RESPIRATORY SYSTEM. 



Bronchi. Both run obliquely downward and outward, and 

 divide into branches for the lobes. Their structure is that of 

 the trachea. The right bronchus is the wider and more verti- 

 cal; the pulmonary artery crosses its continuation below its 

 branch to the upper lobe, which is thus eparterial. The left 

 bronchus is twice as long; the pulmonary artery crosses it 

 above all the branches, which are thus hyparterial. [975] 



Pleura. A central vertical partition (mediastinum thoracis), 

 extending from the spine to the anterior thoracic wall, divides 

 the thoracic cavity into two lateral, or pleural, cavities. A 

 serous membrane (pleura) lines each cavity and is prolonged 

 onto the lung at its root, investing it completely. The part 

 (visceral pleura) investing the lung is very thin and firmly ad- 

 herent. The part (parietal pleura) lining the chest wall is 

 arbitrarily divided according to its location (though all parts 

 are continuous) as follows: The cervical pleura is the dome- 

 shaped roof of the cavity, rising one-half to one and a half inches 

 above the clavicle and grooved on top by the subclavian artery; 

 an expansion holds it to the first rib. The costal pleura lines 

 the chest walls, from the sternum to the bodies of the verte- 

 brae. The diaphragmatic pleura lines the diaphragm external 

 to the pericardium. The mediastinal pleura extends on the 

 side of the mediastinum from front to back, except where it 

 passes on to the intervening root of the lung; a doubled fold 

 (ligamentum latum pulmonaris) is prolonged downward from 

 the root of the lung, stretching between the lung and pericar- 

 dium, and ends below in a free border. [977] 



Lines of Pleural Reflection. The costal and mediastinal 

 pleurae are continuous behind (posterior or vertebral line) 

 along the front of the spine; the lines on the two sides are well 

 apart above, and equidistant from the mesial plane, but grad- 

 ually approach below, and also deviate to the left. These two 

 pleurce are continuous in front (anterior line) along the back 

 of the sternum ; the lines of the two sides begin at the sterno- 

 clavicular joints, come together just above the gladiolus, and 



[137] 



