Dr. Latuam’s Effay on the Tracheee or Windpipes of Birds. 95 
tending to the above circumftances, be moft times got at the know- 
ledge of; but we cannot thereby difcriminate the /pecies. And it is alfo 
more difappointing, that, at fome feafons of the year, in particular 
fubjeéts, thefe internal marks are fo nearly obliterated as to deceive 
a very good comparative anatomift, and much lefs likely to be afcer- 
tained by any one who may be but flightly verfed in fuch matters. 
But the particular circumftance of the trachea, as will hereafter be 
pointed out, never alters; except in being more or lefs complete in 
its period of offification during the life of the bird. I ought not 
however toomit, that in a very careful comparifon many traits of 
difference between one fpecies and another may be detected by the 
fkilful anatomift (although fuch may not have either labyrinth, or 
any enlargement of the trachea to diftinguifh them by), arifing 
from the ftructure of the rings themfelves, aided by the mufcles ap- 
propriated to their motion ; and it may be with confidence afferted, 
that one mean at leaft, if not the principal, of producing a loud 
noife, and on the contrary, may arife from the peculiar conftruction 
of thefe tracheal rings, which in many birds are found to be more or 
lefs complete in themfelves; fome of them wanting even a large 
portion of the circle, whilft others are not only perfect, but of a 
ftrong and elaftic ligamentous nature, and fome few fo greatly indu- 
rated asto approach almoft to the texture of bone*.—Added to which 
is the great difference of mufcular appendages; for,in the birds which 
have a weak voice, the mufcles are fo likewife: on the contrary, very 
{trong mufcles are obfervable in thofe whofe cry is loud, by which 
ftructurethe rings, the ftrength of which is ever proportional, are 
put into violent aétion, and the bird thereby enabled to throw out 
the air with great forcef. It is certain, alfo, that, in birds which 
* Asin the Peacock, Goofanders, Smew, and fome others. 
+ See acurious and elaborate differtation on this fubje&in ALegazin Encyclopédigue; 
tom. ii. p. 334 et feq. 5 
I ling. 
