THOKAX. 139 



SPLAXCHIVOLOGV. 



Pleura. — Serous membriine lining tlie thoracic cavity, 

 forming two sacs resting on each otlier and the medi- 

 astinum. The anterior mediastinum is that portion sit- 

 uated in front of the heart ; tlie posterior is the one 

 posterior to tliat organ. The costal pleura lines the 

 internal face of the ribs; the diaphragmatic pleura lines 

 the anterior face of the diaphragm muscle. With the 

 mediastine pleura, they form the parietal layer of tliat 

 serous membrane. The pulmonary pleura covers the 

 external face of the lungs and forms the viceral layer. 

 This membrane receives blood vessels, and also nerves 

 from the sympathetic, pneumogastric, diaphragmatic 

 and intercostals. 



Bronchia. — Terminal branches for the trachea, one 

 for each luug, they divide in this tissue, aifecting the 

 dichotomic division. The right bronchia is the largest. 

 They are perfectly cylindrical to their end, and'^Fe 

 composed of cartilaginous rings formed by elongated 

 small pieces of cartilages resting upon each other by 

 their extremities, (tliese disappear in the smallest tube,) 

 and of a muscular layer lining the whole extent of the 

 tube, which is covered by a mucous membrane. They 

 receive divisions of the bronchial arteries, veins and 

 nerves. Lymphatics pass to the bronchial glands. 



