ORGANS OF THE BODY. 451 



passages has been given by Sclmlze (fig 431, It; 432, c). They are sub- 

 divided again at acute angles, and end finally in peculiar dilatations (431, 

 b; 432, a). These are the so-called primary pulmonary lobules. They 

 are of short conical figure, and have received from Rossiynol the name of 

 infundibula. 



These primary lobuli correspond, to a certain extent, with the primary 

 lobules of the racemose glands, and are like them made up of terminal 

 vesicles, as a rule roundish, but polyhedral when strongly distended. 

 They are always met with on the surface of the organ in this form. 



There is, however, a difference between the two. While the saccules, 

 namely, of every genuine racemose gland remain more or less distinct 

 from one another, the analogous parts of the respiratory organs, to which 

 the names air cells, pulmonary vesicles, alveoli, or Malpighian cells, have 

 been given, are far less isolated. They appear to be rather saccular 

 dilatations in the walls of the primary lobules, in which no further 

 canals are to be discovered, all the alveoli, on the contrary, opening 



Fig. 433. Transverse section through the substance of the ]ung of a child of nine months 

 (after Ecker). 6, a number of air vesicles enveloped in elastic fibrous networks winch, 

 together with a thin structureless membrane, form the walls of the same; d, a portion 

 of the capillary network of the part, with its tendril-like tubes projecting into the 

 cavities of the alveoli; c, remains of epithelium. 



directly into a common cavity. In the adult body, moreover, absorption 

 of the walls between the several air cells of an infundibulum may take 

 place (Adriani). 



The side walls of the alveolar passages are also thickly covered with 

 numbers of similar pulmonary vesicles (fig. 431, c, c). 



In sections of pulmonary tissue (fig. 433) the more or less round or 

 oval form of the vesicles may be recognised in the open spaces of varying 

 size brought into view (b}, agreeable to the description just given. 



The diameter of the alveoli is generally stated as ranging between 

 0-1128 and 0'3760 mm. Their great elasticity admits, of course, during 

 life, of their dilatation to a great degree, so that, as we would expect, the 

 vesicles are, at the end of inspiration, much larger than during expiration. 



