232 The Wmdfye. [Book IX. 



complete circles, but are imperfect behind, where the 

 circle is completed by a foft but ftrong glandular and 

 mufcular membrane. The cartilaginous rings are thin 

 and elaftic, but thicker and broader before than at their 

 fides. They are largeft at the upper part of the wind- 

 pipe, and are found to be fmaller as we advance lower. 

 Of the mufcular fibres fituated between the cartilagi- 

 nous rings, fome are circular, which render the wind- 

 pipe narrower, and others longitudinal, which render it 

 fhorter. 



The windpipe in the upper part of the cavity of the 

 thorax is divided as was before ftated into two great 

 branches, the larger and fhorter of which goes to the 

 right lobe of the lungs, the fmaller and longer to the 

 left. 



The ftru&ure of the branches of the windpipe, till 

 they enter the fubftance of the lungs, is the fame as that 

 of the windpipe j after they enter'the lungs, however, 

 the cartilaginous rings foon difappear, and nothing but 

 a thin elaftic coat remains. The ultimate divifions of 

 the windpipe terminate in the air-vcffels of the lungs. 



