454 DISSECTION OF THE PIGEON. 



pleura, an anterior continuation of the peritoneum. 

 Their inner edges he close together, separated from 

 each other in the median plane by the projecting 

 centra of the thoracic vertebrae, and by the dorsal 

 aorta. 



Remove the pleura from the ventral surface of one lung ; 

 and separate the lung from the thoracic wall, noting its close 

 attachment to this wall, and the grooves in its surface which 

 lodge the ribs. 



3. The syrinx, or ' lower larynx,' is the organ of voice of 



the , pigeon, and is formed by the dilated hinder 

 end of the trachea, and the commencement of the 

 bronchi. 



Cut across the trachea about an inch in front of its bifur- 

 cation. Make two lateral incisions, with scissors, along the 

 sides of the trachea and bronchi, and turn down the ventral 

 wall. 



i. The tympanum is the cavity of the lower end 

 of the trachea and commencement of the 

 bronchi. 



ii. The membrana tympaniformis interna is the 

 mucous membrane lining the inner wall of 

 the commencement of each bronchus. 



iii. The membrana semilunaris is a delicate vertical 

 fold of mucous membrane extending for- 

 wards into the tympanum from the angle of 

 bifurcation of the trachea : by its vibration 

 the voice is produced. 



iv. The pessulus is a slender bar of cartilage run- 

 ning across the tympanum, in the substance 

 of the membrana semilunaris, from the dorsal 

 to the ventral surface. 



4. The structure of the lungs. 



Pass a seeker along one of the bronchi, and slit it open 

 with scissors. Follow the branches of the bronchus through 



