174 
his excellent Essay on the Trachea', or 
Wind-pipes of Birds, has done more to-, 
wards the elucidation of this subject than 
any other writer, or than the productions of 
all his predecessors. Willoughby and 
other early writers upon Ornithology, had 
observed Nature's deviations from the usual 
structure in the formation of the Trachea y 
in different species of birds, some, gave it 
as their opinion that it served to increase 
the tone of voice. Others have supposed 
that the peculiarity of structure might be 
of use in diving. As far as the deviation 
from a cylindrical shape is concerned, it is 
observable that the peculiar difference in 
structure is to be found only in the male 
sex, the female never having the least en- 
largement in that part ; for although many 
birds may be found having the female 
plumage, in which the labyrinth is equally 
conspicuous with the other sex, yet we 
may venture to assert, that this part does 
not in the least differ from that in the adult 
male, except that the ossification is less 
complete, and we have no doubt that in 
every specimen where such enlargement of 
