ORGANS OP RESPIRATION. 



241 



enclosed in a periosteum. The cartilage rings are held 

 together by a strong elastic fibrous tissue, which not 

 only occupies the space between them but is pro- 

 longed over their surfaces, so that each ring appears 

 imbedded in this tissue. Each cartilage terminates 

 abruptly behind by rounded ends, between which 



Fig. 186. Transverse section through human bronchus (Bohm and 

 Davidoff). 



stretches a thin layer of smooth muscle tissue. This 

 muscle not only unites the ends but is also found in 

 the intervening space between the cartilage rings, 

 along the posterior wall of the trachea. Outside of 

 the transverse fibers are a few fasciculi having a lon- 

 gitudinal direction. 



The cartilage rings of the bronchi resemble those 



16 



