140 EQUINE ANATOMY. 



LungSi — General disposition: Essential organs of 

 respiration, divided in two lateral moieties, described 

 as the right and left lung, tlie former being the larger. 

 Form : Together they have the form of the thoracic 

 cavity, each representing half of a cone with two faces, 

 three borders, a base and an apex. 



Faces. — External is convex; internal offers an ante- 

 rior part resting on the anterior mediastinum, an exca- 

 vation for the reception of tlie heart, the root of the 

 lungs ; a posterior part resting on the posterior medias- 

 tinum, the thoracic groove and oesophageal fissure. The 

 right lung has also a small lobule on that face. Base : 

 Concave and moulded on the anterior face of the 

 diaphragm ; on the right lung it has a deep notch for 

 the posterior vena cava. Apex : Forms tlie anterior 

 lobule of the lung. Borders : Superior is convex 

 and rests in the vertebro-costal groove ; the inferior 

 is thin, with a large notch on the left lung for the 

 heart ; tlie posterior bounds the base or diaphragmatic 

 face. Structure : Serous envelope, the pleura. Tissue 

 proper, of a rose color, soft but resisting, elastic, very 

 light, divided in small lobules by conjunctive partitions, 

 each lobule being formed of pulmonary vesicles col- 

 lected and comnmnicating together witli a bronchial 

 tube ; each vesicle has a membrane proper lined by 

 pavimentous epithelium and is covered with capillajy 



