368 CHIKANOSUKE OGAWA 
the outer lung wall, accordingly in them the muscle fibers take 
the course parallel to the outer wall. In the outer lung wall I 
noticed weak muscle bundles similar to those in Gecko. 
3. Muscle fibers in Aves 
It is already known that muscle tissue is not foundin the 
respiratory canaliculi, but they form circularly arranged muscle 
fibers in flute-holes. My investigations have not revealed any 
further differences. According to Piso-Borme’s statement, birds 
capable of long flights have large numbers of muscle fibers around 
the flute-holes, but this statement seems to me rather unfounded. 
4. Muscle fibers in Mammalia 
Whether the muscle tissues are present in the alveolar system 
of mammalian lungs has been a much-debated question. But no 
conclusion has yet been drawn from a large literature. One 
reason for the lack of agreement in the reports of various observers 
is the difficulty in distinguishing the muscle tissue from the other 
tissue of the lung, especially from the other connective tissue. 
Where a number of muscle fibers constituting a bundle and 
having a regular arrangement are present, they are distinguished 
from the other tissues, but in instances where they are distributed 
singly in other tissues it is difficult to distinguish them by dif- 
ference in staining. The form of nucleus of the muscle cell alone 
may be used as a criterion. Hirschmann says that the muscle 
cells can be distinguished by the form of the nucleus with certainty. 
Eberth holds that the form of the nucleus of the muscle cell can- 
not be used as a mark of distinction. I think both statements 
go to the extreme. If the form of the nucleus and the condition 
of its presence are taken into consideration, then it is not impos- 
sible to judge the existence of the muscle cells in other tissues. 
With the present microscopic technique we have no better way 
of determining their presence. 
The thick sections are necessary for study of the alveolar 
system, but on the other hand the use of them makes it difficult 
to discover the muscle cells. Another reason for the disagree- 
