THE RESPIRATORY SYSTEM 139 
which an anteroposterior slit-like opening forms the 
glottis ; there is no epiglottis. This is only an air passage, 
the voice being made in the syrinx or lower box which lies 
at the bifurcation of the trachea. The structure of the 
upper box is quite simple with its lateral plates controlled 
by the glossal muscles and two external retractors but 
the syrinx is very complicated and variable in the dif- 
ferent orders and even in the same family. It possesses 
an internal and external set of muscles and in some birds 
can be opened at one point to permit air to pass to the 
cervical or thoracic air sacs. Detailed discussion of its 
anatomy is hardly profitable since there is nothing 
peculiar about its diseases. On one occasion only have 
we seen distinct pathological change — what was probably 
an extension of mould disease from it to the cervical air 
sac. It is involved in true tracheitis and bronchitis but 
even these are rare in birds. 
The larynx on the other hand is constantly reddened 
in cases of pharyngitis and may be the seat of mould 
colonies. Edema of this structure is, however, not very 
common, it being recorded but tmce in birds in associa- 
tion with nearby inflammation and five times in mammals ; 
in the latter cases three were of acute infectious nature, 
one was a tumor and the other osteomalacia. It is 
common to find the laryngeal and tracheal mucosa swollen 
and wet in chronic bone degenerations without the con- 
dition being severe enough to call it edema. 
Laeyngitis. 
Acute laryngitis of active catarrhal or purulent nature 
has been met five times in mammals and twice in birds 
while more chronic lesions have occurred only in the 
former, four times. Tuberculous laryngitis has been 
observed in a cockatoo and a lemur ; they are interesting 
enough to cite. There are no cases recorded among 
monkeys despite the large number dying from the disease ; 
this implies of course that no suspicion of its existence 
