THE VISCERA. 



231 



front and at the sides cylindrical, it is formed of from seventeen 

 to twenty cartilages placed one above the other, and of the shape 

 of the letter O ; behind, flat and membranous. 



Cervical portion. 1. Before and above, covered by isthmus 

 gl. thyreoid., mm. sterno-thyreoidei and fasc. cervicalis, below 

 by much uniting tissue (Art. thyreoidea), and a little by Art. 

 anonyma. 2. At the sides: Gl. thyreoidea, A. carotis comm., 

 n. vagus, lymphatic glands. 3. On the posterior surface : ceso- 

 phagus (which projects rather to the left), n. recurrens dexter 

 and sinister (which passes towards the left side). 



Dorsal portion, in the mediastinum posticum. Before it lie, 

 from above downwards: Sternum and m. sterno-thyreoid, V. 

 subclavia sinist. and truncus anonymus, the posterior portion of 

 Arcus Aortse, and Art. pulmonalis (bifurcation) ; behind it: (Eso- 

 phagus; on the sides : Pleura, Nn. vagus and recurrens (superior 

 part); a quantity of uniting tissue and lymphatic glands. 



The Bronchi are the two branches of the trachea, into which it divides 

 before the third dorsal vertebra. The obtuse angle of division (bifurcation) 

 is filled up by a triangular ligament and the blackish bronchial glands. The 

 bronchus dexter, one inch long, about eight lines thick, consists of five to six 

 O shaped cartilaginous rings, divides into three branches with which it enters 

 into the right lung, and lies close under the bend of V. azygos, behind V. cava 

 superior and Art. pulmonalis dextra. Bronchus sinister, two inches long, about 

 five lines thick, consists of from ten to twelve O shaped cartilages, divides 

 into two branches for the two lobes of the left lung, lies under the arcus 

 Aorta and obliquely before the (esophagus, behind Art. pulmonal. sinistra and 

 before aorta descendens. Between each bronchus and Artt. pulmonales we find 

 the Vv. pulmonales. The branches of the bronchi again ramify and always 

 dichotomously (bronchia) until at last they terminate in the pulmonary vesi- 

 cles. Vessels : Artt. bronchus come from the Aorta ; Vv. bronch. enter the V. 

 azygos (upon the right side), the v. intercost. (upon the left). 



Structure. 1. The cartilaginous rings are placed at tolerably equal inter- 

 vals, horizontally above one another, the interspaces filled up with fibrous 

 rings. Flexible and elastic in the young, they frequently ossify as age ad- 

 vances. Of unequal vertical diameter (1^ to 2^ lines), several of them fre- 

 quently unite together. The vertical diameter of the first is the greatest. 

 The last, the longest, is turned downwards, has behind an acute angle where 

 the first Bronchial rings pp.ss off. 2. The fibrous membrane (perichondrium) 

 commences at the inferior border of the cartilages to which it passes as lig. 

 crico-tracheale, covers both surfaces of the cartilages, fills the interspaces, and 

 assists (with the other membranes) to form the posterior flat wall of the 

 trachea and bronchi, which is attached by uniting tissue to the oesophagus. 3. 

 Transverse, smooth muscular fasciculi, between the posterior extremities of 

 the cartilages approximate these to one another. 4. Yellow, elastic bundles 

 of fibres, pass parallel to the long axis on the internal surface of the muscular 

 coat. 5. The mucous membrane is thin, paler man in the larynx, firmly 

 attached (without folds), and perforated by numerous openings, which are the 

 openings of small, flat, oval glandul. tracheales, which are situated between the 

 mucous and muscular coats. 



