Examine the photographs of the shark's olfactory sac and
eye by clicking the blue lettered links in the column to the right.
The olfactory sacs are spherical structures that contain
a series of radial folds called olfactory lamellae. Their surfaces are covered
with olfactory epithelium. Sea water taken into the nares is passed over
these sensory areas. Here the odors stimulate the cilia-like endings of
neuro-sensory cells.
The olfactory bulbs are a paired anterior extension of
the brain leading into the posterior end of the olfactory sacs. Their fibers
continue into the olfactory tract and the olfactory lobe of the cerebral
hemisphere.
The sclera is the tough white fibrous outer coat of the
eye. At places it is made even more firm by cartilage embedded in the sclera.
The iris is the pigmented anterior extension of the choroid
layer. In its center is the pupil. The iris regulates the size of the pupil.
In the living shark the lens is a clear and flexible structure
located behind the iris. It helps to focus the light upon the light sensitive
retina.
The retina is the multi-layered sensory gray-white colored
membrane. The rods and cones which receive light stimuli are located here.
The optic nerve leaving the eye is a continuation of the light receptor
cells in this membrane. |