138
D. J. RANDALL
portal hearts contract while the branchial heart is inactive. Johansen
(1960) recorded large oscillations in the dorsal aortic blood pressure in
Myxine glutinosa that were associated with contractions of the gill musculature and suggested that the gills take an active part in the propulsion
of blood. Chapman e t al. (1963) did not observe any effect of gill contractions on blood flow in the Pacific hagfish.
The velocity of the pressure pulse through different parts of the circulatory systcm has not been measured in fish. Nothing is known about
the reflection of pressure waves from arborizations in the circulation
or the contribution of reflected waves to the pulse pressure at any point
in the circulation.
111. THE HEART
A. Anatomy
The systemic or branchial heart of fishes is the main propulsive organ
for circulating the blood. It consists of four chambers in series (Fig. 1 ) .
Venous blood enters the sinus venosus from the liver and the ducts of
Cuvier, passes into the atrium, and is then pumped into the ventricle
and finally into the ventral aorta, via either a conus (Chondrichthyes
and Dipnoi) or bulbus (teleosts) arteriosus. All chambers with the
exception of the bulbus are contractile, and a unidirectional flow through
the heart is maintained by valves at the sinoatrial and atrioventricular
jun'ctions and at the junction of the ventricle and bulbus or conus. The
contractile conus wall consists of a thin layer of cardiac muscle covering a fibrous elastic sheath, and it may have up to seven transverse
rows of valves along its length. The bulbus, elastic and noncontractile,
has only a single pair of valves guarding the exit of the ventricle.
The heart of the cyclostome is similar to that of other fish except that
there is only a single duct of Cuvier in the adult (paired in other fish),
and the conus is poorly developed. The exit of the ventricle is guarded
by a pair of pocket valves, but there are no other valves in the conus.
In Petromyzon, however, there are two longitudinal ridges similar to
those found in the embryonic conus of other forms.
The heart of the lungfish (Johansen and Hanson, 1968) is somewhat
diff ercnt from the typical fish pattern described above. The heart lies
behind the pectoral girdle; the sinus and atrium dorsal to the ventricle.
The atrioventricular valves are absent and are replaced by an atrioventricular plug. There is a partial subdivision of the heart by the
D. J. RANDALL
portal hearts contract while the branchial heart is inactive. Johansen
(1960) recorded large oscillations in the dorsal aortic blood pressure in
Myxine glutinosa that were associated with contractions of the gill musculature and suggested that the gills take an active part in the propulsion
of blood. Chapman e t al. (1963) did not observe any effect of gill contractions on blood flow in the Pacific hagfish.
The velocity of the pressure pulse through different parts of the circulatory systcm has not been measured in fish. Nothing is known about
the reflection of pressure waves from arborizations in the circulation
or the contribution of reflected waves to the pulse pressure at any point
in the circulation.
111. THE HEART
A. Anatomy
The systemic or branchial heart of fishes is the main propulsive organ
for circulating the blood. It consists of four chambers in series (Fig. 1 ) .
Venous blood enters the sinus venosus from the liver and the ducts of
Cuvier, passes into the atrium, and is then pumped into the ventricle
and finally into the ventral aorta, via either a conus (Chondrichthyes
and Dipnoi) or bulbus (teleosts) arteriosus. All chambers with the
exception of the bulbus are contractile, and a unidirectional flow through
the heart is maintained by valves at the sinoatrial and atrioventricular
jun'ctions and at the junction of the ventricle and bulbus or conus. The
contractile conus wall consists of a thin layer of cardiac muscle covering a fibrous elastic sheath, and it may have up to seven transverse
rows of valves along its length. The bulbus, elastic and noncontractile,
has only a single pair of valves guarding the exit of the ventricle.
The heart of the cyclostome is similar to that of other fish except that
there is only a single duct of Cuvier in the adult (paired in other fish),
and the conus is poorly developed. The exit of the ventricle is guarded
by a pair of pocket valves, but there are no other valves in the conus.
In Petromyzon, however, there are two longitudinal ridges similar to
those found in the embryonic conus of other forms.
The heart of the lungfish (Johansen and Hanson, 1968) is somewhat
diff ercnt from the typical fish pattern described above. The heart lies
behind the pectoral girdle; the sinus and atrium dorsal to the ventricle.
The atrioventricular valves are absent and are replaced by an atrioventricular plug. There is a partial subdivision of the heart by the