458 THE RESPIRATORY AI'I'AltATfs f\ MAMMALIA. 



loft, tho arch of tho aorta and tho thoracic duct. Tho latter is sometimes 

 carried to the opposite side. 



STRUCTURE. Tho trachea comprises in its structure : the cni-iiliujlm.im 

 rings which form its base ; tho ligaments whicli xinito theso rings ; tho 

 mucous membrane spread over its inner face ; a nmxrnlur /<////, which only 

 linos that membrane superiorly ; and vessels and nerves. 



Fig. 230. 



THE RESPIRATORY ORGANS; INFERIOR, OR FltONT VIEW. 



1, Trachea; 2, Jugular vein; 3, Great rectus anticus muscle; 4, Carotid artery; 

 5, Longus colli muscle; 6, Origin of the common carotids; 7, V.-rt. l.ral :irtrry ; 

 8, Section of first rib; 9, Cephalic trunk of right axillary artery; 10, Anterior 

 lobe of right lung; 11, Middle, or supplementary lobe of ditto ; 12, Posterior 

 portion or lobe of ditto ; 1:5, Heart; 14, Cardiac artery ; 15, Ventricular branch 

 of cardiac vein ; 16, (Esophagus. 



Cartilaginous rings of the trachea. Those are about fifty in number, 

 and do not form perfect rings, being incomplete on the upper side of tho 

 trachea. Each is a kind of arc, composed of a cartilaginous plate flatt< IK .1 

 and curved on itself, whoso extremities are turned towards each other, and 



