1086 



SPLANCHNOLOGY 



The further subdivisions of the bronchi will be considered with the anatomy of 

 the lung. 



If a transverse section be made across the trachea a short distance above its 

 point of bifurcation, and a bird's-eye view taken of its interior (Fig. 963), the septum 



FIG. 962. Bronchi and bronchioles. The lungs have been widely separated and tissue cut away to expose the air-tubes. 



(Testut.) 



placed at the bottom of the trachea and separating the two bronchi will be seen 

 to occupy the left of the median line, and the right bronchus appears to be a more 

 direct continuation of the trachea than the left, so that any solid body dropping 

 into the trachea would naturally be directed toward the right bronchus. This 



tendency is aided by the larger diameter 

 of the right tube as compared with its 

 fellow. This fact serves to explain why 

 a foreign body in the trachea more fre- 

 quently falls into the right bronchus. 1 



Structure (Fig. 964) The trachea and extra- 

 pulmonary bronchi are composed of imperfect 

 rings of hyaline cartilage, fibrous tissue, mus- 

 cular fibers, mucous membrane, and glands. 

 ,, Qft o T, The cartilages of the trachea vary from sixteen 



Fia. 963. Transverse section of the trachea, just . , , J 



above its bifurcation, with a bird's-eye view of the to twenty in number: each torms an imperfect 

 interior. ring, which occupies the anterior two-thirds or 



so of the circumference of the trachea, being 



deficient behind, where the tube is completed by fibrous tissue and unstriped muscular fibers. 

 The cartilages are placed horizontally above each other, separated by narrow intervals. They 

 measure about 4 mm. in depth and 1 mm. in thickness. Their outer surfaces are flattened in 

 a vertical direction, but the internal are convex, the cartilages being thicker in the middle than 



1 Ileigel asserts that the entry of a foreign body into the left bronchus is by no means so infrequent as is generally 

 supposed. See also Med.-Chi. Trans., Ixxi, 121. 



