Agriculture Reference
In-Depth Information
accessory lacrimal gland. The lacrimal apparatus consists
of the lacrimal gland, the lacrimal caruncle, the lacrimal
canals, the lacrimal sac, and the nasolacrimal duct. The
lacrimal gland is located dorsolateral to the eyeball, the
tears run toward the medial angle of the eye, where a little
elevation, the lacrimal caruncle, is located. Through two
lacrimal canaliculi, the tears are accumulated into the lac-
rimal sac; and from there through the nasolacrimal duct,
they exit on the fl oor of the nasal vestibule.
macrosmatic animal with an abnormally keen olfactory
sense). The olfactory organ has a chemical sense starting
from chemoreceptors located within the olfactory mucosa
of the dorso-caudal part of the nasal cavity. Neurosensory
olfactory cells (the chemoreceptors), sustentacular cells,
and basal cells are included in the olfactory epithelium.
For detailed information, please consult histology topics
(for example, Eurell and Frappier, 2008).
The Gustatory Organ
The gustatory organ consists of taste buds located on the
surface of the tongue and pharynx. These buds send the
information to the brain where it is processed in sensations
of taste or gustation. The taste buds consist of taste cells,
which are the receptors. It is mandatory that in order to be
tasted, a substance must be dissoluble. The fungiform and
vallate papillae are gustatory. The taste buds on the surface
of fungiform papillae in the goat are abundant in compari-
son with the other ruminants. The taste buds of the vallate
papillae are located in the epithelium surrounding the
papillae. All taste buds have the role of perception. It is
known that the goat is able to discriminate bitter, sweet,
salty, and sour tastes (Smith and Sherman, 1994). Three
cranial nerves send the information to the brain, where it
is processed as the sense of taste. For details please consult
histology topics as previously advised.
The Ear
The ear is the organ of hearing and equilibrium and consists
of three parts: the external, the middle, and the internal ear.
The external ear is represented by several structures, but
the only one that is externally visible is the auricle. The
position of the auricle in the goat is vertical. The auricles
are big (see Figure 6.40) and located under the horns. The
internal surface of the auricle is concave, called scapha,
and is provided with several irregularities.
The middle ear consists of the tympanic cavity, the
tympanic membrane, the auditory ossicles, and the audi-
tory tube. The tympanic cavity is sculpted within the tem-
poral bone. The tympanic membrane (the drum) separates
the external ear from the middle ear. It vibrates under the
various intensities and qualities of sounds, which are trans-
mitted to the internal ear via the auditory ossicles (malleus,
incus, stapes, and the little lenticular bone). The stapes
transmits the sound vibrations to the internal ear, whereas
the malleus is in contact with the drum. The middle ear is
connected with the nasopharynx by the pharyngotympanic
(auditory, eustachian) tube.
The internal ear is located in the temporal bone, in the
so-called osseous labyrinth. It converts the mechanical
stimuli of sounds, and the gravity and positional changes
of the body into nerve impulses. The impulses are trans-
mitted to the brain by means of the CN VIII (the vestibu-
locochlear nerve). Within the osseous labyrinth, the
membranous labyrinth is represented by ducts and cavities
fi lled with a fl uid called endolymph. The space between
the osseous and the membranous labyrinth is fi lled by a
shock - absorbing fl uid called perilymph. The saccule, the
utricle, the three semicircular ducts, and the cochlear duct
complete the membranous labyrinth.
The Touch Organ (Common Integument)
The common integument including the skin and cutaneous
organs is very complex. It consists of epidermis, dermis,
hair, horns, pads, hooves, cutaneous glands, and mammary
glands. Some of these were already described. The cutane-
ous sense will be briefl y described along with particular
hairs, cutaneous appendages, and cutaneous glands.
The sensory organs of the skin are receptors for tem-
perature, pressure, tension and pain, and they allow the
central nervous system to keep contact with the environ-
ment. The skin, therefore, is the organ of touch (Nickel
et al., 1981), but primarily, it functions as a protective
barrier against the environment.
The skin consists of three major layers: epidermis,
dermis (corium), and hypodermis. The epidermis is the
external layer of the skin, which becomes keratinized in
the horn of the hoof (see The Digital Organ), and the
external layer of the horn. The corium is thicker than the
epidermis. Skin glands (sweat and sebaceous) are located
in, and hairs originate from, the corium. The hypodermis
is the connective tissue layer connecting the skin to the
underlying structures.
The Olfactory Organ
The olfactory organ or the sense of smell is not very well
developed in the goat, a reason that this species is among
the large group of microsmatic animals (versus the dog, a
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