VOL. LVI.] PHILOSOPHICAL TRANSACTIONS. 331 



and then rises in that round direction, till it enters the cavity of the thorax, and 

 is divided into two branchiae, which terminate in the lungs. 



When one views this structure, it is impossible to avoid being surprized at the 

 wonderful formation of this part, especially too if we attend to the noble contri- 

 vance for securing these circular volutions of the pipe, from compressing one 

 another, or from bending into angles ; for, if this was the case, their long and 

 free respiration could not be maintained, and the end, for which the pipe is so 

 formed, would not be answered. An explanation of this contrivance will be 

 necessary in this place : there is a strong membrane, which arises from all the 

 clavicle, and is inserted all along the jugal bone on each side, very stiff like a 

 drum ; and as the aspera arteria makes its anterior volutions between the latter, 

 (for the posterior turning is that loop within the keel of the sternum described,) 

 it was necessary that the pipe should be supported by a stay in each circular sweep, 

 to prevent the impediments just mentioned. Accordingly there are three strong 

 transverse ligamentous membranes, running from one jugal drum to the other; 

 over the outer of which, the pipe goes into the keel of the sternum through the 

 under hole, and, in its return, rides over two others in a circular direction, in 

 its way to the thorax. These are the stays, which prevent its doubling back in 

 an angle, in these two volutions ; and in that within the theca there was no need 

 of such a fulcrum, being secured in its bed from any external pressure. 



This wild swan was brought alive from Philadelphia, but died soon after its 

 arrival ; and Dr. P. assisted in the dissection, and made these drawings from the 

 prepared parts. He found no mention of this structure of the aspera arteria in 

 the wild swan*, but originally in Bartholin, who took delight in comparative 

 anatomy, from whom Blasius has taken it. 



It is difficult to say what may be the real use of this kind of wind-pipe, in 

 the several birds that have it, if it be not to procure them a longer retention of 

 inspired air, (while they seek their food where they are obliged to remain some 

 time immersed in water,) than if the pipe was straight, as in geese, ducks, and such 

 like; for these and the river swan often dive down to feed, yet it is always in 

 shallow places, and their continuance under water is very short; whereas the 

 wild swan dwells upon and seeks his food in great lakes, and arms of the sea, 

 and dives into deeper waters, and consequently requires a power of continuing 

 longer without respiration than the others. 



Poets and natural historians in great numbers have asserted that these birds 

 sing very harmoniously; and this gave occasion to a friend of Dr. Ps., to whom 

 he showed these drawings, to surmise that this structure might be of use to 

 them in singing; but Dr. P. never found any one who would say they ever 



* Mr. Edwards found it in the swan he describes. See his History of Birds. — Orig. 



