THE LUNGS. 



129 



nular in its structure, has no excretory tube, but very large lym- 

 phatic vessels. It. is supplied by the superior and inferior thyroid 

 arteries. It is sometimes much enlarged, constituting bronchocele 

 or goitre. 



THE LUNGS. 



The lungs are the organs of respiration properly ; they are two 

 in number, and situated in the thorax, placed side by side, being 

 separated from the abdomen by the diaphragm. The size varies 

 with the capacity and condition of the thorax, age, inspiration, ex- 



Fig. 113. 



piration, and disease. They are conical in shape, are longer pos- 

 teriorly than anteriorly, and have concave bases. The colour of the 

 lungs is of a pinkish-gray, mottled with black ; these black spots are 

 more numerous in adult life than in infancy. 



The right lung is shorter but larger than the left, whose transverse 

 diameter is somewhat diminished by the position of the heart. It 

 has three lobes, the left having but two. 



The structure of the lungs is spongy, and its compression between 

 the fingers produces a crackling called crepitation. .It consists of a 

 number of air-vesicles held together by cellular tissue, called pa- 

 renckynia ; through which blood-vessels and air-vessels are rami- 

 fied, A certain number of air-cells communicate with each other, 

 and with a single branch of the bronchial tube ; these are separated 



