RESPIRATORY SPACES OF THE LUNGS SHAD, 
of the ducts, as in the mole. Also in the bat the alveolar wall 
fibers are a little coarser than in the mole (fig. 27). 
Epimys (rat). There are_a great many more elastic fibers 
throughout the rat than in either the mole or bat. The fiber 
rings around the mouths of the alveolar ducts are very marked 
and consist of loose bundles composed of coarse and fine fibers. 
The fiber rings around the alveolar mouths also consist of many 
coarse fibers, which, when they cross each other, spread and 
interlace, forming a confused net (fig. 28). 
This same picture was seen in the bat, although it was not 
evident enough to deserve description. 
Cavia (guinea pig). No remarkable difference from the rat 
ean be confirmed. 
Lepus (rabbit). The fibers are remarkably rich and present 
the same arrangement around the mouths of the alveolar ducts 
and alveoli as in the preceding mammals, but the fibers in the 
alveolar walls differ slightly. Here we have often one or two 
thick fibers in addition to the fine fibers. These thick fibers 
pursue a course through the alveolar wall so that they unite with 
either the fiber ring where they started or an adjoining one. 
During this course the fibers have different appearances, namely, 
sometimes it divides itself in several less thick fibers, sometimes 
not, in either case it gives off finer fibers to the alveolar walls. 
The thick fibers show no wavy winding. At departure from the 
fiber ring the thick fiber is made by the union of many fine fibers, 
although seldom it begins at the ring in a single fiber. 
Felis (cat). The arrangement and thickness of the fibers are 
about the same as in the rabbit. The elastic fibers in the alveo- 
lar walls often cross one another and sometimes there is a mutual 
exchange of fibers. In the above-mentioned mammals the elas- 
tic fibers of the blood-vessels give some fibers to the alveolar 
walls, but this process is especially evident in the lung of the 
eat, with the result that both coarse and fine fibers branch from 
the walls of the blood-vessels into the mouths of the alveolar 
ducts, as well as the alveoli, and into the adjacent alveolar walls. 
Capra (goat). The difference from the cat seems to be that in 
this mammal the elastic fibers are a little richer. 
