7. THE LABYRINTH
223
about all possible axes. Fundamentally, therefore, it is perfectly feasible
to postulate that the utriculus alone is capable of controlling all postural
responses ( Lowenstein, 1932, 1936). However, the evidence from the
work on elasmobranchs shows that in these animals at least the lagena
has an important graviceptor role. During tilts its responses run counter
to those of the utriculus insofar as the majority of units are found to have
maximum discharge rates in or near the “normal” position of the skull
in space. It is quite likely that further scrutiny might disclose more units
the maximum activity of which occurs in the upside-down position. This
guess is based on the presence in the near vertically extended macula
lagenae of hair cells pointing dorsally interspersed with others pointing
ventrally. It is also likely that the lagena may respond more sensitively
to fore-and-aft than to lateral tilts.
The macula sacculi lies in a near dorsoventral plane on the ventromedial aspect of the recessus sacculi. The hair cell map is simple. Two
populations of hair cells are divided by a longitudinal line. Above it they
point upward, below it downward. There is very little overlap along the
dividing line. A scrutiny of the gravity responses from the posterior part
of the sacculus shows similarities with those obtained from the utriculus.
It might be expected that further electrophysiological mapping might
show a preponderance of responses to lateral tilting since it is difficult to
point to a topographically suitable substrate for a response to pure foreand-aft tilts. A further extrapolation from topography would be to expect
good maxima nearer the normal and upside-down position during fullcircle lateral tilts, in contrast to the lagena in which these maxima may
preponderate in the course of fore-and-aft tilting.
The survey of the situation in the elasmobranch labyrinth based on
published data may now be followed by a resume of results of work on
the cyclostome labyrinth in Myxine and Lampetra carried out during the
past few years by the author and collaborators. The labyrinth of the
lamprey, Lampetra fluviatilis ( Lowenstein et al., 1968), contains an
otolith-covered sensory epithelium clearly divisible into areas which
may or may not be true homologs of the maculae of the gnathostome
labyrinth (Fig. 9 ) . The interesting feature of these maculae is the continuity of the sensory epithelia and also of the overlying otolithic mass.
The epithelium of the vertical macula is connected with that of the
anterior and posterior horizontal maculae by upward twisting regions
in which the hair cell pattern is transitional. In the vertical macula, the
hair cells are arranged in two populations divided by a longitudinal
line above and below which they point upward and downward, respectively, There is little overlap. This hair cell arrangement is identical with
that of the gnathostome sacculus. The arrangement of the hair cells in
223
about all possible axes. Fundamentally, therefore, it is perfectly feasible
to postulate that the utriculus alone is capable of controlling all postural
responses ( Lowenstein, 1932, 1936). However, the evidence from the
work on elasmobranchs shows that in these animals at least the lagena
has an important graviceptor role. During tilts its responses run counter
to those of the utriculus insofar as the majority of units are found to have
maximum discharge rates in or near the “normal” position of the skull
in space. It is quite likely that further scrutiny might disclose more units
the maximum activity of which occurs in the upside-down position. This
guess is based on the presence in the near vertically extended macula
lagenae of hair cells pointing dorsally interspersed with others pointing
ventrally. It is also likely that the lagena may respond more sensitively
to fore-and-aft than to lateral tilts.
The macula sacculi lies in a near dorsoventral plane on the ventromedial aspect of the recessus sacculi. The hair cell map is simple. Two
populations of hair cells are divided by a longitudinal line. Above it they
point upward, below it downward. There is very little overlap along the
dividing line. A scrutiny of the gravity responses from the posterior part
of the sacculus shows similarities with those obtained from the utriculus.
It might be expected that further electrophysiological mapping might
show a preponderance of responses to lateral tilting since it is difficult to
point to a topographically suitable substrate for a response to pure foreand-aft tilts. A further extrapolation from topography would be to expect
good maxima nearer the normal and upside-down position during fullcircle lateral tilts, in contrast to the lagena in which these maxima may
preponderate in the course of fore-and-aft tilting.
The survey of the situation in the elasmobranch labyrinth based on
published data may now be followed by a resume of results of work on
the cyclostome labyrinth in Myxine and Lampetra carried out during the
past few years by the author and collaborators. The labyrinth of the
lamprey, Lampetra fluviatilis ( Lowenstein et al., 1968), contains an
otolith-covered sensory epithelium clearly divisible into areas which
may or may not be true homologs of the maculae of the gnathostome
labyrinth (Fig. 9 ) . The interesting feature of these maculae is the continuity of the sensory epithelia and also of the overlying otolithic mass.
The epithelium of the vertical macula is connected with that of the
anterior and posterior horizontal maculae by upward twisting regions
in which the hair cell pattern is transitional. In the vertical macula, the
hair cells are arranged in two populations divided by a longitudinal
line above and below which they point upward and downward, respectively, There is little overlap. This hair cell arrangement is identical with
that of the gnathostome sacculus. The arrangement of the hair cells in