138 EQUINE ANATOMY. 



Structure. 



The cartilaginous rings are incomplete above, where the space 

 is filled in by transverse muscular and fibrous bands. The rings 

 are united by fibrous tissue which fills the intervening space. The 

 last ring is often divided into two segments for the bronchi by a 

 median spur. 



Mucous Membrane. 



Is covered by ciliated epithelium, and its glands are very num- 

 erous posteriorly. 



Vessels. 



From carotid and axillary. 



Nerves. 



From recurrent laryngeal. 



BRONCHI. 



The right and left primary bronchi are the continuation of the 

 trachea, enter the root of each lung with the bronchial artery, veins 

 and nerves. They then subdivide into a large number of branches 

 which go on subdividing further. They are round, composed of 

 cartilaginous circles joined to each other by muscular fibre. The 

 cartilages and muscles disappear when the tubes become small. 

 The mucous membrane is much more sensitive than that of the 

 trachea, otherwise like it. 



Vessels. 



Bronchial. 



Nerves. 



From sympathetic and tenth. 



THE LUNGS 



Are the essential organs of respiration, situated in the thorax on 

 either side of the heart and enveloped by a serous membrane — 

 the pleurae. They are described as two lungs, the right and left. 

 Each lung is cone-shaped and has an external face lying against 

 the ribs ; an internal, forming the side of the mediastinum, which 

 shows notches for the oesophagus and aorta ; the root of the lung, 

 where the bronchi, vessels and nerves enter its structure, and the 

 attachment of the ligamentum latu7n pulmonis, a process of the 

 pleura passing backward to the diaphragm ; a base, concave and 

 in contact with the diaphragm ; it shows a small lobule on the right 



