338 



TEXT-BOOK OF PHYSIOLOGY. 



Bronchiole 



Alveolar 



chus. From the sides of the terminal bronchus and from its final 



termination there is 

 given off a series of 

 short branches which 

 soon expand to .form 

 lobules or alveoji (Fig. 

 15*97! Thfe cavity of I 

 the alveolus is termed 

 the infundibulum. From] 

 the inner surface of the 

 alveolus and of the pas- 

 sageway leading into it, 

 there project thin parti- 

 tions which subdivide 

 the outer portion of the 

 general cavity or infundi- 

 bulum into small spaces 

 or sacs, the so-called 

 air- sacs (Fig. 160). The 

 wall of the alveolus is 

 extremely thin and con- 

 sists of fibre-elastic tis- 



Infundibulum. 



FIG. 159. SCHEME OF A BRONCHIOLE TERMINAT- 

 ING IN ALVEOLAR PASSAGES, THOSE LEADING 

 INTO INFUNDIBULA BESET WITH AIR-CELLS. 

 (Landois and Stirling.) 



sue, supporting a very 



elaborate capillary network of blood-vessels. The bronchial system 

 as far as the alveolar passages is lined bv 



ciliated epithelium. The aij^sacs are lined 

 by flat epithelial plates of irregular shape, 

 termed ihevespimtory epithelium (Fig. 161). 

 The alveoli are united one to another by 

 fibre-elastic tissue. 



The lungs in the physiologic condition 

 occupy the greater part of the cavity of the 

 thorax. They are separated from each 

 other by the contents of the mediastinal 

 space: viz., the heart, the large blood-vessels, 

 the esophagus, etc. Each lung is somewhat 

 pyramidal in shape with the apex directed 

 upward. The outer surface is convex and 

 corresponds to the general conformation of 

 the thorax. The inner surface is concave 

 and accommodates the contents of the medi- 

 astinal space. At about the middle of the 

 inner surface there enter the lung, the bron- 

 chi, and blood-vessels. The under surface 

 of the lung is concave and rests "on^he diaphragm. The posterior 



FIG. 1 60. SINGLE LOBULE 

 OF HUMAN LUNG. a. 

 Alveolar passage, b. 

 Cavity of lobule or in- 

 fundibulum. c. Pul- 

 monary sacs. (Dai- 

 ton.) 



