92 Dr. Larwaw’s Ejay onthe Trachea or Windpipes of Birds: 
Tortoife, in the Philofophical Tranfa€tions*. ‘It is'by means of the 
above refources, added to the obfervations I have myfelf made for a 
number of years, that I fhall endeavour to elucidate the fubject as 
far as in my powet; and although I may not be able to determine 
the matter with fo great a degree of precifion as might be wifhed, 
it is more than probable that others, hereafter, will be able to com- 
plete the ftru€ture of which I have endeavoured to lay the ground 
work. 
I fhall begin this effay by obferving, that in moft birds the natu- 
ral fhape of the trachea, afpera arteria, or windpipe, by all which names 
this part is known, is that of a regularly uniform cylinder of equal 
diameter, or nearly fo, throughout, from its rife at the root of the 
tongue, to its entrance into the hollow of the zhorax, frernum, or breafl= 
bone, where it divides into two branches, called bronchie, which ramify 
into air-veffels which compofe the two lobes of the lungs. This, 
I fay, is the general mode of conftruction: but Ornithologifts pretty 
far back} have noticed nature’s deviation from this ufual ftruéture, 
both in refpeét to the various curvatures of the windpipe itfelf, as 
well as the difference of fome from others in refpect to conformas ° 
tion; but their fentiments were penned in too vague a manner to 
determine much thereon, not an{wering the purpofe further than 
to ftimulate our future refearches. As far as the deviation from a 
cylindrical fhape is concerned, it is obfervable that the peculiar dif- 
ference in ftructure is feen only in the male fex, the female not having 
the leaft enlargement, or increafed cavity, as will hereafter be 
mentioned: but to what purpofe nature has intended this, is, I be- 
lieve, at prefent unknown to us. Some authors have given as their 
opinion, that the enlargement of the ¢rachea in males, whenever 
* Vol.-lvi. p. 204. 
+ Aldrovandus, Willughby.—See alfo Birch’s Hift. hey Soc. ii. p. 13 
