THE LUNGS. 1843 



tinum ; the spinous process of any dorsal vertebra, with the exception of the first, 

 eleventh, and twelfth, denotes the situation of the posterior extremity of the rib 

 articulating with the transverse process of the vertebra immediately below ; the tips 

 of the spinous processes of the first, eleventh, and twelfth dorsal, vertebrae are above 

 rather than opposite the transverse processes of the vertebrae immediately below ; 

 the space between the ends of the transverse processes and the angles of the ribs 

 varies from one to two and a half inches, according to the numerical position of the 

 rib ; the incomplete rings of the bronchi render those tubes easily recognizable by 

 touch ; they are found about an inch and a half anterior to the opening in the 

 thoracic wall. 



THE LUNGS. 



The lungs are a pair of conical organs, each enveloped in a serous membrane, — 

 the pleura, — occupying the greater part of the cavity of the thorax, and separated from 

 each other by the contents of the mediastina. Although in general conical, the lung 

 differs in many respects from a true cone. The base is concave, moulded over the con- 

 vexity of the diaphragm, and descends farther at the back and side than at the front 

 and mesially. The apex is not over the middle of the base, but much to the inner 

 and posterior side of it, so that the back and inner side of the lung descend much 

 more directly than the rest. The right lung is the larger on account of the greater 

 encroachment of the heart on the left. 



The surfaces of the lungs are the base, the external surface (which is the 

 mantle of the cone from apex to base, and embraces all the periphery from the front of 

 the mediastinal space around the wall of the thorax to nearly opposite the front of the 

 vertebral column), and the ^nesial or mediastinal surface. 



The borders are the inferior, which surrounds the base, and the anterior and 

 posterior, which bound respectively the back and front of the internal surface. 



The external surface (fades costalis), much' the largest, is closely applied to 

 the portion of the wall of the pleural cavity formed by the ribs and the intercostal 

 muscles. The region of the apex is a part of this surface. It rises slightly — possibly 

 I cm. — above the oblique plane of the first rib, which indents it towards the front. 

 The apex itself is in the internal and posterior part of this region. It rests closely 

 against the firm fibrous structures that roof in this region, and is grooved trans- 

 versely by the subclavian artery, more anteriorly on the right lung than on the left. 

 A slight groove made by the subclavian vein may be found in front of the arterial 

 one. The rest of the external surface is smooth, except where it may be slightly 

 depressed beneath the individual ribs. It should be noted that a part of what is 

 termed the external surface faces inward against the vertebral column and the first 

 part of the ribs as they pass backward. The external surface descends lowest at the 

 back and at the side. 



The mesial surface (fades mediastinalis) is approximately plane, except for 

 the cardiac fossa, which is much deeper on the left than on the right, and extends as 

 far as the lower surface. The left lung presents a shelf-like projection from behind 

 under this fossa. The other chief feature of the internal surface is the hilum for the 

 entrance of the structures composing the root of the lung. It is situated nearer the 

 back than the front and below the middle, being behind and above the cardiac fossa. 

 The outline of the hilum in the left lung is approximately oval, with the lower end 

 sharpened and the long diameter vertical. It is more triangular in the left lung, as 

 the root expands forward near the top. The position of the bronchi and the chief 

 vessels as they enter the lungs differs on the two sides. Right lung : the chief bron- 

 chus enters at the middle or lower oart and its first branch near the top, ,both being 

 at the back of the hilum ; the pulmonary artery, generally in two branches, enters one 

 branch in front of the main bronchus and the other in front of the secondary bronchus, 

 but at a higher level ; the superior pulmonary vein is high and in front of the higher 

 arterial branch ; the inferior, often subdivided, is near the lower end of the hilum ; one 

 branch may be in front of the bronchus and one below it. Left lung : the bronchus 

 enters the back of the hilum rather above the middle ; the pulmonary artery is at the 

 top, sometimes in two divisions ; the superior pulmonary vein is high up in front. 



