26 ANATOMICAL CONSIDERATIONS. 



Such a condition of parts imagines the windpipe also able to alter its 

 dimensions, so that it may be in accord with other structures; and 

 anatomy discloses facts which amply support such a supposition. The 

 larynx or opening to the windpipe is composed of several pieces of car- 

 tilage and of numerous muscles. The presence of the first plastic and 

 highly elastic structure is a proof that the larynx is of no fixed shape, 

 while the division of the organ into distinct parts, together with the 

 internal and external presence of many muscles of motion, is absolute 

 confirmation that the larynx was created not only to assume various 

 forms, but also to exhibit different capacities, according to the require- 

 ments of the animal economy. 



So also with the windpipe itself, and the tubes which proceed from 

 it; these are formed of distinct rings, or of separate pieces of elastic 

 cartilage so curved as to form rings, but having free overlapping ends, 

 which are operated upon by muscular fiber. 



The diagram inserted below accurately represents such a ring; it 

 also shows that the springy cartilage is not made of one thickness 

 throughout, but is of that form which the mechanic of the present 

 time recognizes as that best adapted for the preservation of continued 

 elasticity. The shape and the free ends convinces that such a ring 

 must always have a tendency to expand, and by this perception we 

 recognize the purpose of the muscle, which draws the extremities over 

 each other ; thus two opposing forces regulate the capacity of the circle. 



ONB OP THE OAEHLAOIKOUS BINOS, NUMBERS OF WHICH JOINED TOOBTHEE 70RM THE TEAOHEA OE THE 

 WINDPIPE OP THE HOESE. 



a One of the cartilages from the trachea of a horse, having free and overlapping extremities. 

 6 The muscular fiber situated within the ring, which regulates the diameter of the circlft 



The presence of muscular fiber is always absolute proof of motion. 

 Where muscle exists and morbid circumstances render motion an impos- 

 sibility, the function being destroyed, the motor organ becomes paDid, 



