. A system of anatomy for the use of students of medicine (Volume 1). and are so arranged in the membrane, that theykeep the tube completely open. These portions of cartilage donot continue throughout the whole extent of the ramifications;for they become smaller, and finally disappear, while the mem-branous tube continues without them, ramifying minutely, and Fig. 41* probably forming the air-cells ofthe lungs. This membrane is very elastic:the lungs are very elastic also; andit is probable that their elasticityis derived from this membrane. On the inside of this coat ofthe trachea is an arran
. A system of anatomy for the use of students of medicine (Volume 1). and are so arranged in the membrane, that theykeep the tube completely open. These portions of cartilage donot continue throughout the whole extent of the ramifications;for they become smaller, and finally disappear, while the mem-branous tube continues without them, ramifying minutely, and Fig. 41* probably forming the air-cells ofthe lungs. This membrane is very elastic:the lungs are very elastic also; andit is probable that their elasticityis derived from this membrane. On the inside of this coat ofthe trachea is an arrangement ofmuscular fibres, which may becalled a muscular coal. It is bestseen by peeling off orremovingtheinternal coat, to be next described. g__ On the membranous part ofthe trachea, where the cartilagi-nous rings are deficient, thesemuscular fibres run evidently ina transverse direction: in the * ;r. 41, represents the larynx, trachea,and bronchia; on the right side is seenthe lung; on the left, the lung has been destroyed to show the ramification of the 40*. 474 0F THE TRACHEA. spaces between the cartilages their direction is is some reason to doubt whether these longitudinal fibresare confined altogether to the spaces between the cartilaginousrings, and attached only to their edges, because there is a fleshysubstance on the internal surface of the rings, which appears tobe continued from the spaces between them. The internal coat of the trachea is a thin and delicate mem-brane, perforated with an immense number of small foramina,which are the orifices of mucous ducts. On the surface of this membrane there is an appearance oflongitudinal fibres which are not distributed uniformly over it,but run in fasciculi in some places, and appear to be deficient inothers. These fasciculi are particularly conspicuous in the rami-fications of the bronchia in the lungs. —Many of the German anatomists have described these aslongitudinal muscular fibres, the object
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