. The structure and life of birds . astonishing ; andwhen we consider the variety of functions which itssmall body has to perform its musical powers supplyfar greater reason for wonder. The air-sacks, no doubt,are a great assistance. Those great reservoirs of airmust make it easier for the bird to avoid the awkwardcrises that come to the untrained human vocalistwhen he finds, at the moment his grandest notes areexpected of him, that his voice is becoming thin andfeeble for want of breath. The trachea sometimestakes strange forms which might be thought to influ-ence the voice. In the Drake, jus
. The structure and life of birds . astonishing ; andwhen we consider the variety of functions which itssmall body has to perform its musical powers supplyfar greater reason for wonder. The air-sacks, no doubt,are a great assistance. Those great reservoirs of airmust make it easier for the bird to avoid the awkwardcrises that come to the untrained human vocalistwhen he finds, at the moment his grandest notes areexpected of him, that his voice is becoming thin andfeeble for want of breath. The trachea sometimestakes strange forms which might be thought to influ-ence the voice. In the Drake, just in front of the syrinx,it has a big box-like appendage, which looks as if itmight be intended to give the voice greater resonance. 140 THE STRUCTURE AND LIFE OF BIRDS CHAP. This great air-chamber is entirely wanting in the the quack of the Duck is loud and sonorous, thatof the Drake is thin and without any body in it. Insome species of Crane, the trachea winds roundabout within the keel of the breastbone, which is trb cl. Fig. 35, showing convolutions of Trachea of Mantchurian Crane. b, Network of bones ; br, Trachea dividing into two bronchi; cl, Clavicle; co, Cora- coid ; sc, Scapula ; tr, Trachea at entrance into keel. formed of two thin sheets with, in places, a light bonynetwork in between : after all these windings it atlength divides and enters the lungs. Cranes have aloud and striking crow, but it is not nearly so strikingas the crow of the barndoor Cock, whose windpipetakes the shortest course to the lungs. The whistling V1 FORM AND FUNCTION 141 Swan shows convolutions of the trachea very similarto those of the Crane. Whatever other purpose it mayserve, the long coiled windpipe ensures the thoroughwarming of the air before it reaches the lungs. Muscles and Tendons. To muscles all movement in the body is acted on by the motor nerves they contractand become shorter, with the result that the bone orother organ connected with them is moved. Thenerve, i
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