THE TRACHEA. 461 



Form. The bronchial tubes are not flattened like the trachea; a 

 transverse section shows them to be regularly cylindrical. 



Volume. The left bronchus is always smaller than the right, and both 

 are much inferior in volume to the aggregate of their respective branches. 



Relations. Each bronchus enters the pulmonary lobe along with the 

 blood-vessels, which with it forms what is called the root of the lung. The 

 divisions of this arborescent trunk are accompanied by the bronchial artery, 

 vein, and nerves, which ramify in the same manner. 



Near their origin, the bronchi are related to the bronchial glands, above 

 which, and to the left side, passes the oesophagus. 



STRUCTURE. The structure of the bronchial tubes resembles that of the 

 trachea ; their walls being formed by a cartilaginous framework, a muscular 

 layer, mucous membrane, and vessels and nerves. 



Cartilages of the bronchi. These only exist in tubes of a certain calibre, 

 the minute passages being deprived of them, and having only membranous 

 walls. As in the trachea, this framework includes, for each tube, a series 

 of transverse rings joined border to border ; though these are no longer 

 formed of a single arciform piece, but each results from the union of several 

 lozenge-shaped pieces whose extremities overlap, and which are united to 

 each other, like the cartilaginous segments of the neighbouring rings, by 

 means of cellular layers, and also by the membranes spread over their 

 internal surface. 



Muscular layer. Extended in a very thin continuous layer over the 

 entire inner surface of the cartilaginous rings, this layer disappears in the 

 smallest bronchial tubes. 



Mucous membrane. This membrane is dis- Fi gt 233. 



tinguished from that of the trachea by its great 

 sensibility; it alone constitutes the walls of 

 the terminal bronchial divisions. (When the 

 cartilages terminate, the tubes are wholly mem- 

 branous, and the fibrous coat and longitudinal 

 elastic fibres are continued into the ultimate 

 ramifications of the bronchiaB. The muscular 

 coat is disposed in the form of a continuous 

 layer of annular fibres, and may be traced upon 

 the smallest tubes ; it is composed of the un- 

 striped variety of muscular fibre.) 



Vessels and nerves. The vascular and ner- 

 vous branches distributed in the tissue of the " 



TUBE H HE 



, 1 i . r /? ,i i-iTi i CHI AL TUBE, WITH THE 



bronchial tubes come from the satellite vessels LARIES INJECTED. 



and nerves of these tubes the bronchial arteries, 



veins, and nerves. The lymphatics pass to the bronchial glands. 



DIFFERENTIAL CHARACTERS IN THE AIR-TUBE SUCCEEDING THE NASAL CAVITIES IN OTHER 



THAN SOLIPED ANIMALS. 



RUMINANTS. In the Ox, SJieep, and Goit, the interior of the larynx is simpler than in 

 the Horse, and the lateral ventricles and vocal cords are almost effaced. The most 

 important differences in its various pieces are as follows : 1, The thyroid cartilage has 

 no anterior appendices, but is provided, posteriorly, with two considerable prolongations 

 that articulate with the cricoid cartilage (it has no excavation between the two wings, 

 and is formed by a single piece ; its inner face, in the middle, near the lower border, has a 

 small fossette to which a round and very salient tuberosity on the external face corres- 

 ponds) ; 2, The upper border of the cricoid is not notched in front (neither is the bezel on 

 its lower border) ; 3, The epiglottis is wider, but less acute, than iu Solipeds (Leyh says it 



