368 



CHORD ATA. 



by small bony rings ; those of the bronchi, except the first, 

 are of cartilage. At the junction of the trachea and bronchi 

 is the syrinx, the true organ of voice in the birds. The 

 bronchus passes into the lung and there branches. Its 

 branches emerge from the lung to open into the air-sacs 

 already noticed. The lungs themselves are dense, rather 

 small, and closely pressed against the ribs. They lie dorsal 

 to the coelom and their ventral face only is covered by peri- 

 toneum. The air taken into the lungs can pass freely into 

 the air-sacs. The bird respires in a different manner to the 

 frog. The air is drawn through the lungs into the air-sacs 

 and is expelled forcibly again by the movements of the 

 body-muscles. The lungs themselves have only a small 

 respiratory surface, correlated with the free current of air 

 through them. 



Fig. 260. — Ventral View^ of Male 



Urogenital Organs of the 



Pigeon. {Ad nat.) 



Testis. 



Vas Deferens. 

 Ureter. 



Kidney. 



Swollen Base of i ^, ^ 



Va. Deferens. bctweCn 



The general form and 

 position of the kidneys 

 have been already de- 

 scribed. A small ureter 



urogenital. Pf^^^^ ^^"^ 

 the ventral 



face of each kidney 



backwards into the 



cloaca. There is no 



urinary bladder. 



In the male the testes 



are paired and situated 



just in front of, and 



Cloaca. 



the kidneys. 

 They are oval, white 

 bodies, and each gives 

 off a fine, twisted tube, 

 the vas deferens, passing backwards into the cloaca. 



In the female the single left ovary lies between the 

 anterior lobes of the kidneys. It is fastened by a dorsal 

 mesentery and usually contains eggs of various sizes. The 

 left oviduct is a large, coiled tube with an internal funnel 

 near the ovary. It opens posteriorly into the cloaca. 

 There is a vestige of the right oviduct. 



The brain is easily exposed by scraping off the dorsal 

 surface of th- skull. The usual parts are all present and 



