Comparative Anatomy
Sensory Organs
Kardong
Chapter 17
Part 16
Sense Organs
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

Monitor external and internal environment
Somatic or visceral receptors
Specific or general
Special Somatic Receptors
Neuromasts



In skin of fish and amphibians
Monitors mechanical, electrical, and
chemical stimuli
Ampullae of Lorenzini in shark snout
Figure 16.1. Ampullae of Lorenzini in shark.
Special Somatic Receptors (cont.’d)
Neuromasts



Pit organs along shark gill
region
Lateral line canal
 Linear series
Derived from ectodermal
placodes
Figure 16.2. External openings of neuromast
organs in Squalus.
Figure 16.3. Neuromast organ and lateral line canal in a fish.
Special Somatic Receptors
Membranous Labyrinth



Vertebrates have pair of fluid filled
membranous labyrinths
Filled with endolymph
Surrounded by perilymph
Figure 16.5. Membranous
labyrinths of human.
Figure 16.4. Left membranous labyrinth of craniates;
semicircular canals (1, 2, & 3), sacculus (s) and
utriculus (u).
Fig. 16.6. Membranous labyrinths of vertebrates (book figure 17.34).
Special Somatic Receptors (cont.’d)
Membranous Labyrinth
The vestibular apparatus


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Semicircular canals,
utriculus, and sacculus
Inside canals:
 Otoliths
 Sensory hairs - perceive
motion (modified
neuromast)
Angular acceleration
detected by the cristae of
semicircular canals
Linear motion and gravity
detected by maculae of
utriculus and sacculus.
Figure 16.7. Vestibular apparatus.
Figure 16.8. Human anatomy of the ear.
Figure 16.9. Anlagen of amniote inner ear (otocyst). Embryonic
head (a) and cross section of head (b).
Special Somatic Receptors (cont.’d)
Membranous Labyrinth

Lagena
Out pocketing of
sacculus wall
 Gives rise to cochlea in
mammals


Organ of Corti
Figure 16.10. Cochlea and organ of
Corti in mammal.
Special Somatic Receptors (cont.’d)
Membranous Labyrinth


Weberian ossicles
 Fish transmit sound waves
 Modified transverse
process
Sinus impar (some fish)
 Assists in transport of
sound
(a)
Figure 16.11. (a) Weberian ossicles (b) Weberian
apparatus for transmitting swim bladder vibrations to ear.
(b)
Special Somatic Receptors (cont.’d)
Membranous Labyrinth
Middle Ear of Tetrapods


Canal from evagination of 1st
pharyngeal pouch
Eustachian tube

Communication between
pharynx and middle ear
Figure 16.12. Position of Eustachian
tube.
Outer, Middle, and Inner Ear of a Bat
Figure 16.13. Bat ear
(book figure 17.44).
Special Somatic Receptors (cont.’d)
Membranous Labyrinth
Middle Ear of Tetrapods

Bones:
Malleus, incus, and
stapes
 Derived from 1st and 2nd
visceral arches
 Stapes is columella in
reptiles and birds

Figure 16.14. Middle ear bones.
Special Somatic Receptors (cont.’d)
Membranous Labyrinth
16.15. Sensory receptors: Cristae (in semicircular canals)and maculae (within sacculus
and utriculus of inner ear (book figure 17.45).
Special Somatic Receptors (cont.’d)
Membranous Labyrinth
Middle Ear of Tetrapods
Figure 16.16. Development of the middle ear bones.
Special Somatic Receptors (cont.’d)
Outer Ear of Tetrapods
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Pinnae
Ear drum set back into skull

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Tympanic membrane on outside
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
Crocs, birds, and mammals
Frogs
External auditory meatus

Canal leading to tympanic membrane
Special Somatic Receptors
Infrared Receptors



Pits that open to surface
 Between epidermal scales
Loreal pits
 Pit vipers
 Between nostril and eye
 thermosensitive
Labial pits
 Pythons
 Other thermosensitive pits
 Appear similar to neuromasts
16.17. Infrared receptors in snakes
(book figure 17.30).
Special Somatic Receptors
Light Receptors
Pineal Complex
Depending upon the species,
the epithalamus may evaginate to
produce up to four discrete organs.
• Paraphysis (most anterior)
• Dorsal sac
• Parietal organ – no retinal image
• Epiphysis
(two or more present = Pineal complex)
Fig. 16.19. Pineal complex (a). Generalized
parietal eye (b) (book figure 17.28)
Special Somatic Receptors
Light Receptors (cont.’d)
Figure 16.20. Pineal complex in lower vertebrates (book figure 17.29).
Pineal Complex
(cont.’d)
Figure 16.21. Parietal eye of iguana (book
figure 17.19).
Special Somatic Receptors (cont.’d)
Light Receptors


Median eye (3rd or pineal eye)
(con’t)
 Part of epiphyseal (pineal)
complex
 Anterior parapineal is often
photosensitive
 Lamprey- both epiphysis
and parietal organ
Both photosensitive
 Lizard- parietal becomes 3rd
eye
Frontal organs
 3rd eye in larval frogs
 Photosensitive
Figure 16.22. Epiphyseal (pineal) complex
of lamprey and embryonic and adult lizard.
Special Somatic Receptors
Light Receptors


Photoreceptors
Lateral eyes
A reflective surface, the
tapetum lucidum,
is found in the choroid
layer in some nocturnal
mammals and produces the
“eye-shine” in car headlights
Figure 16.23. Lateral eyes
(book figure 17.18).
Special Chemoreceptors
Olfactory Organs

Ectodermal placodes
 Sink into head
 Internal naris- opening inside
 Lungfish and tetrapods
 External naris- opening outside
 Fish
 Higher vertebrates possess both
types
Figure 16.24. Internal and external naris
shown and vomeronasal organ.
Special Chemoreceptors (cont’d.)
Olfactory Organs

Vomeronasal organ
(Jacobson’s Organ)
Olfactory mechanisms
isolated form nasal
 Snakes and lizards
 Insert forked tongue into
organ

(a)
(b)
Figure 16.25. Snake collecting scent
molecules (a) that are then delivered to
the vomeronasal organ by the tongue (b).
Snake Vomeronasal Organ (cont.’d)
Figure. 16.26. Tongue flicking (book figure 17.14).
Special Chemoreceptors
Organs of Taste


Taste buds
 Similar to neuromasts
In oral cavity and pharynx
Figure 16.27. Anatomy of the
taste bud.
Special Chemoreceptors
Organs of Taste (cont.’d)
Figure 16.28. Distribution of taste buds on the human tongue (book figure 17.15).