368 CHORDATA. 
by small bony rings; those of the bronchi, except the first, 
are of cartilage. At the junction of the trachea and bronchi 
is the syzinx, 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 ccelom and their ventral face only is covered by peri- 
torieum. 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. 
The general form and 
Fig. 260.—VENTRAL VIEW OF MALE position of the Azdneys 
UROGENITAL ORGANS OF THE 
PIGEON. (Ad nat.) 
have been already de- 
scribed. A small ureter 
«4.7 passes from 
testis, Tem the ventral 
face of each kidney 
backwards into the 
cloaca. There is no 
urinary bladder. 
In the male the zestes 
are paired and situated 
just in front of, and 
Swollen Beret ‘between, 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 vight oviduct. 
The brain is easily exposed by scraping off the dorsal 
surface of the skull. The usual parts are all present and 
Vas Deferens. 
Ureter.. 
Cloaca. 
