. The elasmobranch fishes . (hr.) and anterior oblique semicircular (aus.) canals. The posterior utriculus is the posterior connective of the posterior oblique semicircular canal. This frequently, as in Heterodontus francisci {pos., fig. 236d), may be well devel- oped, the two parts of the utriculus being widely separated by the sacculus and endolymphatic duct. The posterior part of the utriculus has its connection with the sacculus by an elliptical aperture () in Squalus, but this connec- tion is much longer in a type like Heterodontus. In Laemargus borealis the posterior part of the utri
. The elasmobranch fishes . (hr.) and anterior oblique semicircular (aus.) canals. The posterior utriculus is the posterior connective of the posterior oblique semicircular canal. This frequently, as in Heterodontus francisci {pos., fig. 236d), may be well devel- oped, the two parts of the utriculus being widely separated by the sacculus and endolymphatic duct. The posterior part of the utriculus has its connection with the sacculus by an elliptical aperture () in Squalus, but this connec- tion is much longer in a type like Heterodontus. In Laemargus borealis the posterior part of the utriculus is connected with the sacculus by a long tube as it is also in Raja clavata (, fig. 237d). The semicircular canals, although assuming dif- ferent degrees of compression, as is shown by a comparison of the compact ear of Heptanchus with the elongate ear of Squalus, are similarly ar- ranged in three planes. One of these planes is an- terior and oblique, another posterior and oblique, and the third horizontal in position. The anterior and horizontal canals join the utriculus proper, pass forward and backward respectively and then downward to their ampullae, which are in close proximity. The posterior canal is similarly a con- tinuation of the posterior part of the utriculus up- ward and backward and downward to its ampulla (figs. 236 and 237b and d). The ampullae (, , and , figs. 236 and 237) are interesting from their terminal relations as end organs of the nerve. A section through such an otic ampulla (fig. 238a) by Retzius (1881) shows the crista acustica {cr.) which is the terminal mass of sense cells capped by the cupula terminalis {cii.). A more detailed view cutting through the am- pulla demonstrates two kinds of cells in the crista. One of these is the support- ing or thread cell {, fig. 238b) and the other is the sense or hair cell (). The latter of these projects into the endolymph of the ampullary cavity and is capable of receiving sensations.
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