RESPIRATORY SYSTEM. 449 



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. 



C«i across the trachea about an inch in front of its bifur- 

 cation. Make two lateral incisions, luith 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 forwards 

 into the tympanum from the angle of bifurca- 

 tion 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. 



Pfiss a seeker along one cf the bronchi, and slit it open 

 loith scissors. Follow the branches of the bronchus through 

 the lungs, and note tJie openings of the various air-sacs de- 

 scribed above (pp. 431-432). 



VII. DISSECTION OP THE RENA.L AND EEPEODUCTIVE 

 SYSTEMS. 



These may conveniently be considered together, because, as 

 in the rabbit, the genital ducts are in both sexes formed from 

 what were originally parts of the excretory system. 



In the male the vas deferens is formed from the meso- 



GG 



