156 
ZOOLOGY, 
not connected with the gills proper, and receiving their blood-supply 
from distinct arteries. 
The oesophagus dilates almost immediately to form the stomach 
(partly concealed in the figure by the liver, Li), which is hardly 
thicker than the intestine {In). This last is of nearly uniform size 
throughout, and after making three or four coils terminates at the 
anus, immediately in front of the urinary and genital apertures. 
The liver {Li) forms an elongated light-brown mass resting upon the 
stomach. The elongated gall-bladder lies between the liver and 
stomach, somewhat imbedded in the substance of the former. There 
is no pancreas, though it is present in some fishes. The spleen {Sp) 
lies between the stomach and intestine, in the mesentery; it is dark 
reddish-brown in color. 
The air-bladder {S) is a single large glistening sac, placed in the 
dorsal part of the body-cavity. The air-bladder normally contains 
only gases. It conceals most of the kidneys, which extend the 
whole length of the body-cavity on either 
side of the middle line, as two long strips 
of a deep though dull red. They i)roject 
beyond the air-bladder in front {Ki) and 
behind {Ki'). 
The ovary is single, and varies greatly in 
size according to the season. In the male 
the sexual glands (testes) are double. 
The heart {Lit) lies in the triangular peri- 
cardial cavity; it consists of two portions, 
the dark colored venous chamber, or auri- 
cle, above, and the lighter-colored arterial 
chamber, or ventricle, below. The auri- 
cle receives from above two large veins, 
one from either side; these veins are called 
the Cuvierian ducts. Furthermore, a large 
vein, the sole representative of the xena 
Drawn cam of higher vertebrates, passes from 
the liver, near its anterior end, through 
the pericardium, and empties into the Cuvierian ducts near their 
common auricular orifice. 
The brain should be exposed from above by carefully removing by 
a knife the skin and thin bones covering the brain-cavity. Begin- 
ning in front, we notice the minute olfactory lobes and the olfactory 
nerves proceeding to the nasal cavities. Behind the olfactory lobes 
lie in succession the cerebral hemispheres {II), optic lobes (§), the sin- 
gle cerebellum {Gb), and, lastly, the medulla oblongata {M). 
A general idea of the two body-cavities, the nervous and vis'^eral, 
Fig. 200.— Transverse section 
through the middle of the 
body of a Gunner. 
by C. S. Minot. 
