THE STRUCTURE AND ACTIVITIES OF A FISH . 171 
enlargement near the heart is called the arterial bulb. 
The blood-vessels 
bringing blood to the 
heart are called veins. 
Do you find the ventral 
aorta, the arterial bulb, 
and a large vein ? Make 
a sketch to show their 
position. 
Sketch a single gill 
from a cod, or other 
large fish. Indicate the 
parts observed. Trace 
the course of the blood¬ 
vessels in an injected 
specimen. 
Internal Structure. 
With a sharp knife 
make a cross-section 
of the body of a fish a 
little in front of the 
anal opening. Sketch 
the appearance of the 
section, showing the 
location of the vertebral 
column or back-bone, 
the spinal nerve within 
the neural cavity, the 
visceral cavity, and the 
muscles surrounding 
all. Do you find any 
large blood-vessels ? 
Place the fish on 
its side in the bottom 
of a pan containing 
water enough to cover 
it. With scissors re¬ 
move the portion covering one side of the digestive 
Fig. 132.— The Circulation of Blood in 
a Fish. A , aortic bulb; Z/, heart; B , 
arteries supplying gills; V\ veins; b, 
veins conveying aerated blood from 
the gills to the dorsal aorta; Z, vessels 
of liver; A\ kidney. 
