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D. J. RANDALL
is directed toward the left side of the atrium, whereas blood from the
systemic circulation is directed into the right side. The partial separation of right and left atrium and ventricle aids the selective passage of
blood from the lung into the left side of the ventricle. There are no
conal valves but there are two folds or ridges, one large the other small,
arising from opposite sides of the internal surface of the conus arteriosus
(bulbus cordis), The free edges of the folds almost touch and act as a
barrier which partially divides the conus into two outflow channels. The
conus twists and turns, and in the anterior region the two ridges fuse to
form a horizontal septum that completely divides the lumen into a dorsal
and ventral channel. Blood from the left side of the ventricle is preferentially directed into the ventral channel and subsequently into the
systemic circulation, whereas blood from the right side of the ventricle
preferentially enters the dorsal channel which directs blood into the two
posterior pairs of branchial arches, one pair of which directs blood to
the pulmonary arteries (Johansen and Hanson, 1968).
The heart in all fishes, with the exception of that of the hagfish, has a
coronary blood supply. The origin of the coronary supply is variable in
lungfish; Neoceratodus, as in teleosts and elasmobranchs, has a coronary
vessel derived from the anterior hypobranchial system. In Lepidosiren
the coronaries arise from the second afferent artery ( Foxon, 1955)- This
transition from an efferent to an afferent origin for the coronary supply
is associated with the absence of a capillary network in the second gill
arch. In addition, this gill arch presumably contains oxygenated blood
returning via the left side of the heart from the pulmonary circulation.
The hagfish branchial heart has no coronary supply, and blood perfusing the heart is almost totally deoxygenated (Chapman et aZ., 1963).
The hagfish heart is only sporadically active and the pressures developed
are small; hence, the work done by the branchial heart is also small compared with that done by other vertebrate hearts. It is possible that heart
work in the hagfish is limited by the absence of a coronary supply. The
extensive development of accessory hearts in hagfish may represent an
attempt to spread the load of circulating the blood in the absence of a
heart capable of prolongcd activity at high work rates. However, the
hagfish branchial h e a t is capable of producing systolic pressures of the
order of 20-30 mm Hg. The heart obeys Starling’s law and when venous
pressures are increased peak intraventricular pressures rise to 30 mm Hg,
and the work done by the heart increases. Such increases in heart work,
if large, may be anaerobic. The hagfish “usually lies virtually immobile
in lightless, frigid marine canyons for very long periods of time” (Chapman et al., 1963, p. 430). When food appears it swings into violent and
effective action. Nothing is known of the changes in blood flow that
may occur during these periods of activity.
D. J. RANDALL
is directed toward the left side of the atrium, whereas blood from the
systemic circulation is directed into the right side. The partial separation of right and left atrium and ventricle aids the selective passage of
blood from the lung into the left side of the ventricle. There are no
conal valves but there are two folds or ridges, one large the other small,
arising from opposite sides of the internal surface of the conus arteriosus
(bulbus cordis), The free edges of the folds almost touch and act as a
barrier which partially divides the conus into two outflow channels. The
conus twists and turns, and in the anterior region the two ridges fuse to
form a horizontal septum that completely divides the lumen into a dorsal
and ventral channel. Blood from the left side of the ventricle is preferentially directed into the ventral channel and subsequently into the
systemic circulation, whereas blood from the right side of the ventricle
preferentially enters the dorsal channel which directs blood into the two
posterior pairs of branchial arches, one pair of which directs blood to
the pulmonary arteries (Johansen and Hanson, 1968).
The heart in all fishes, with the exception of that of the hagfish, has a
coronary blood supply. The origin of the coronary supply is variable in
lungfish; Neoceratodus, as in teleosts and elasmobranchs, has a coronary
vessel derived from the anterior hypobranchial system. In Lepidosiren
the coronaries arise from the second afferent artery ( Foxon, 1955)- This
transition from an efferent to an afferent origin for the coronary supply
is associated with the absence of a capillary network in the second gill
arch. In addition, this gill arch presumably contains oxygenated blood
returning via the left side of the heart from the pulmonary circulation.
The hagfish branchial heart has no coronary supply, and blood perfusing the heart is almost totally deoxygenated (Chapman et aZ., 1963).
The hagfish heart is only sporadically active and the pressures developed
are small; hence, the work done by the branchial heart is also small compared with that done by other vertebrate hearts. It is possible that heart
work in the hagfish is limited by the absence of a coronary supply. The
extensive development of accessory hearts in hagfish may represent an
attempt to spread the load of circulating the blood in the absence of a
heart capable of prolongcd activity at high work rates. However, the
hagfish branchial h e a t is capable of producing systolic pressures of the
order of 20-30 mm Hg. The heart obeys Starling’s law and when venous
pressures are increased peak intraventricular pressures rise to 30 mm Hg,
and the work done by the heart increases. Such increases in heart work,
if large, may be anaerobic. The hagfish “usually lies virtually immobile
in lightless, frigid marine canyons for very long periods of time” (Chapman et al., 1963, p. 430). When food appears it swings into violent and
effective action. Nothing is known of the changes in blood flow that
may occur during these periods of activity.