88 VETBEINARY STATE BOARD 



in which the heart is lodged, and behind this is the root of the lung, 

 formed by the bronchi, blood-vessels and nerves entering the struc- 

 ture, also a fold of the pleura, ligamentum latum pulmonalis, which 

 is attached to the mediastinum and posterior face of the diaphragm ; 

 a base or diaphragmatic face, concave and in contact with the dia- 

 phragm, showing a notch for the posterior vena cava; an apex or 

 summit, situated behind the first rib, forms the anterior lobe; a 

 superior border, thick and convex, rests in the vertebracostal chan- 

 nel or concavity ; an inferior, shorter and thinner, is notched deeply 

 for the heart. 



The right lung has three lobes, an anterior, middle and posterior ; 

 the left, two, an anterior and posterior. 



The lung substance is pink-colored, soft, spongy and elastic tis- 

 sue; it is divided into lobules which are further subdivided into 

 alveoli and air-cells that communicate with bronchioles, the sub- 

 divisions of bronchii. 



Blood supply: nutrient, bronchial arteries; functional, pul- 

 monary arteries. Nerve supply: pneumogastric and sympathetic. 



Describe the different reflections of the pleura and state the different 

 structures to which they are respectively applied. 



1. Costal pleura is applied to the internal face of the ribs and 

 internal intercostal muscles. 



2. Diaphragmatic pleura, a continuation of the costal, is adher- 

 ent to the diaphragm. 



3. Mediastinal pleura separates the two lateral halves of the 

 lungs. It is applied against the internal face of each half and com- 

 prises between its two layers the heart. The portion in front of the 

 heart is called the anterior mediastinum, and that behind, the pos- 

 terior mediastinum. 



The anterior mediastinum contains the trachea, oesophagus, an- 

 terior aorta and its divisions, anterior vena cava, thoracic duct, and 

 the cardiac, pneumogastric, recurrent and phrenic nerves. In the 

 foetus and very young animals, it also contains the thsmius glands. 



The posterior mediastinum is traversed by the posterior aorta, 

 vena azygos, thoracic duct, oesophagus and nerves. 



4. Pulmonary or visceral pleura, a continuation of the medias- 

 tinal, completely envelops the lung-tissue proper. 



Give the relative thickness of the mediastinum in horses and in cattle, 

 and state how this affects conditions in unilateral pleurisy. 

 In its inferior part, the posterior mediastinum of the horse is 

 very thin and perforated by small openings ; whereas, in cattle, it is 



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