RESPIRATORY SPACES OF THE LUNGS 391 
- these fiber rings a few fibers are sent off to the alveolar walls. 
In the bat the fiber rings around the alveolar mouths are supple- 
mented also by the fibers which branch off from the mouths of 
the alveolar ducts and run along the alveolar ducts. In the lung 
of the bat and guinea-pig the elastic fiber rings consist of loose 
bundles of several fibers and the fibers in the alveolar walls be- 
come rich. ‘The elastic fibers in the rabbit lung are richer 
and the thick main fibers appear in the alveolar walls. In the 
goat, cat, dog, and man the fibers increase in closeness. Findings 
by Linser and Orsos concerning the elastic fibers 1 in the human 
lung are sometimes contrary to mine. 
11. Reticular fibers in the lung of Gecko and Elaphe are 
divided into two systems, the fine circular fibers around the blood- 
capillaries and flatly spreading fibers in the subepithelial con- 
nective tissue. In the respiratory canaliculi of the domestic fowl 
and duck the reticular fibers twine themselves around the 
capillaries. 
12. In the lung of the mole and bat a majority of the reticular 
fiber rings around the alveolar ducts and alveoli are composed of 
a single fiber. From the fiber rings of the alveolar mouths several 
fine fibers are given off to the alveolar walls. In the rat and 
guinea-pig the fibers are coarser and closer; the fiber rings consist 
of several fibers. In the guinea-pig the thick main fibers appear 
in the alveolar walls. In the rabbit, cat, dog, and man the 
fibers are very close. Circular fibers around the blood-capillaries 
cannot be confirmed. Reticular fibers of the embryo (ripe 
rabbit embryo) are a little finer, less tortuous, and form looser 
nets. 
13. The elastic fibers of the mouths of the alveolar ducts 
and alveoli are always located superficially to the reticular fibers 
and muscle fibers. 
14. Membrana propria of the alveolar walls is not elastic 
membrane. 
15. The alveolar pores are normally found in many mammals 
and only seldom cannot be seen. 
