404 Chapter 16
LABORATORY
The Digestive System continued
EXERCISE:ventral to the anus. Later in development, the
urogenital opening will separate from the
digestive opening and the single open-ing will
become two. If you have a male, the
urogenital opening will be located posterior to
the umbilical cord. A muscular tube, the
penis, can be felt just under the skin run-ning
forward from between the back legs forward
to the urogenital opening.B.. Internal Features- The oral cavity: open the jaws as much as you
can without cutting. Identify the oral cavity
with the tongue forming the ventral floor. The
hard palate forms the dorsal area or roof of
the mouth. The hard palate sepa-rates the
nasal cavities from the oral cavity. Use
scissors to make a cut from one corner of the
mouth to the bottom of the ear. Use Figure
16 - 17 as your guide and make cut number 1.
You must cut through soft tis-sue and then
through bone (the ramus of the mandible).
Repeat this cut on the other side of the mouth,
being careful not to rip the tissues of the soft
palate in the poste-rior region of the mouth.
Once you have cut through the pig’s jawbone,
you will be able to open the mouth very
widely and you will be able to examine the
internal features of the oral cavity. - Examine the tongue and feel the papillae
scattered over the surface of the tongue. Many
of these contain taste buds. Feel the roof of
the mouth. It is divided into the an-terior hard
palate with its wavelike hard tis-sues and the
posterior soft and delicate soft palate. In
humans, a soft extension of the soft palate
called the uvula hangs down into the throat.
Note that the pig does not have a uvula. The
small opening at the back of the soft palate in
the roof of the mouth is the nasopharynx. This
is the opening from the nasal cavities, which
allows air to enter the pharynx on its way to
the larynx and trachea of the respiratory
system.
3. Now observe the gums and the teeth that have
erupted through the gum tissue. They are
probably canines and incisors. You may cut
into the gums and remove some of the
embryonic teeth. If you have cut back far
enough, you will see at the base of the tongue
a small median flap, the epiglottis. It will pop
out as you pull the jaw down gen-tly. It
partially covers the glottis, which is the
entrance into the trachea, which leads to the
lungs. It prevents food from entering the
respiratory system when swallowing. Poste-
rior and dorsal to the glottis is the esopha-gus,
which leads to the stomach. Try to push your
probe down into the esophagus. We will
observe the esophagus when we dissect the
thoracic and neck region of the pig in Chapter
17. Refer to Figure 16-18 of the fetal pig
dissection for the following.
4. The abdominal cavity: the abdominal cav-ity
is posterior to the ribs where the ventral body
wall is very soft due to the absence of any
bony support. The body wall encloses the
large peritoneal cavity, which contains most
of the digestive, excretory, and repro-ductive
organs. In opening the peritoneal cavity, use
the umbilical cord as a landmark and follow
the dotted lines numbers 3 and 5 of Figure 16-
17. Cut through the soft, thin body wall very
carefully with your scalpel. Once you have
cut through, continue with your scissors. The
quarter moon cut just the diaphragm muscle
that separates the tho-racic cavity (to be
observed in Chapter 17) from the abdominal
cavity. Once you have completed the cut, pin
back the lateral flaps of skin of the abdominal
area. If your cavity is filled with dark brown
clotted blood, take your specimen to the sink
and flush it out. It does not harm or alter your
specimen. It should just be cleaned out to
make your ob-servations clearer.
5. Examine one of the flaps of skin. It is com-
posed of three layers of tissue. The out-ermost
is the skin, followed by a middle