LUNGS OF MAMMALIA. 



573 



443 



- 



ffife 



of which, in most mammals, do not coalesce, but either overlap, 



meet, or, more commonly, fail to meet by about one- fourth, or less, 



of their circumference, fig. 453 5 b. The slit or interval, which is 



usually at the back, or gular surface, of the windpipe, is completed 



by a musculo-membranous sheet. The hoops themselves are 



connected together by a 



strong elastic membrane 



occupying their intervals 



and also extended over 



both their outer and inner 



surfaces. The entire tube 



is invested by loose areolar 



tissue, and is lined by a 



mucous membrane with a 



ciliated free surface. 



The tracheal cartilage, 

 fig. 443, e, consists of a 

 fibrous basis, charged with 

 nucleate cells. Unstriped 

 muscular fibres extend be- 

 tween the ends of the hoop, 



haVlll* their attachment tO Transverse section of trachea through a cartilaginous 

 P hoop, e. CCLXVIII. 



the inner surtace, some 



short way from the end itself, as at k, fig. 443, others pass ob- 

 liquely between contiguous hoops. On the inner surface of the 

 tracheal cartilages and muscles is a stratum of elastic, chiefly 

 longitudinal, fibres, ib. i : their 

 fasciculi are most conspicu- 

 ous, extending in a serpentine 

 course along the back part of 

 the tube. The mucous mem- 

 brane consists of a basilemma, 

 fig. 444, , and of finer areolar 

 tissue, b 9 forming a bed of 



numerous nucleate cells, c, d, 

 the innermost, e, or those next 

 the inner surface of the air- 



tube, being Clavate, and SUp- Section of tracheal ciliate 



porting on their base, each 

 from about twenty to fifty vibratile cilia, so acting as to direct 

 throat-ward the matters with which they are in contact. The 

 mucus lubricating the ciliate surface and entangling any foreign 

 particles admitted with the air, is the secretion of small, for the 



l 



u 



' ' ^-~ ^=^s^ ^ 



mucous membrane, magn 



