148 
A. LIAUTAKD. 
inous band whose two extremities converge towards each other 
like the rings of the trachse. 
And again, the external auditory bony canal, hollowed through 
the thickness of the tuberous portion of the temporal, is closed at 
its bottom by the membrana tympani, which separates the external 
from the middle ear. 
The auditory canal runs partly into the annular cartilage, as 
well as this one does for the cartilage of the concha. 
A peculiar little muscle, the mastoido aurieularis, laying 
against the internal side of the concha, has for duty to bring these 
three parts close together, a very limited motion. 
The skin, at the annular cartilage, assumes characters which 
make it resemble mucous membrane; it contains a large quantity 
of peculiar glands analogous to sebaceous glands, the ceruminous 
glands, which secrete a peculiar substance, untuous, of a yellow¬ 
ish color when fresh, but ordinarily blackened with dust, the ceru¬ 
men which is always found there varying more or less in quantity. 
It is possible that through an exaggerated secretion, this cerumen 
may accumulate in such quantity as to obliterate partly or in toto 
the external auditory canal. Cleanliness, however, remedies this 
trouble easily. In some special cases, by the itching it gives rise 
to by becoming irritating and ranee, the cerumen gives rise to 
symptoms of vertigo. I am unable yet to say if it is this cerumen 
which is the cause of a peculiar affection, which I have seen in 
rabbits, and whose symptoms resemble those of cerebral lesions of 
the pons varolii, or of the cerebellous peduncles. The animal has 
a tendency to roll upon itself, or to turn round. At the post mor¬ 
tem, and already during life, when examining the ears, the audi¬ 
tory canal may be seen filled with concreted pus, and the mem¬ 
brana tympani perforated. The purulent collection has also pen¬ 
etrated in the semi-circular canals and the trochlse. The irrita¬ 
tion produced upon the extremities of the auditory nerve may be 
the cause of the symptoms exhibited by the animals. 
The membrane of the tympanum is a membranous sheet sepa 
rating the external auditory canal from the middle ear; it is oval, 
very thin and slightly concave; its circumference is attached upon 
the tympanal circle, small frame almost circular, but notched above- 
