Download Mudpuppy Dissection

Mudpuppy Dissection
The common mudpuppy, Necturus maculosus, is a member of the Caudata, which
together with Anura (frogs and toads) and Gymnophiona (caecilians or apodans) for the
Lissamphibia. The Caudata, including the salamanders and newts, are the least
specialized amphibians in the body form and locomotion. The body is elongated and
stout, with well-developed axial musculature and tail. Salamanders use their limbs in
combination with the side to side body undulations characteristic of fish, and thus
probably resemble the earliest land vertebrates in locomotion. In contrast, frogs are
characterized by a shortened body and specialized salutatory locomotion, while
gympnophionans are limbless.
Necturus are neotenic (retaining juvenile features) salamanders that retain their larval,
filamentous external gills, two pairs of pharyngeal slits, and caudal fins as adults.
External Anatomy:
Skin
Segmentation
Number of Pharyngeal slits
Symmetry
Regions of Body
Neck
Post-anal tail
Cloaca
Eyelids
External ears
Appendages
Teeth
Internal Anatomy:
Enter the pleuroperitoneal cavity by making a longitudinal incision about 0.5 cm to the
left of the midventral line. Cut anteriorly until you reach the cloacal opening. Gently
spread the abdominal wall. The long elongated dark structure midventrally is the liver.
Examine the posteroventral part of the cavity to observe the thin-walled urinary bladder.
Carefully cut through the falciform ligament, and make two transverse cuts through the
body wall, one on either side, to create four flaps that can be spread apart. The long, light
colored, tubular stomach lies dorsal and slightly to the left of the liver.
The elongated spleen hangs from the posterior left side of the stomach. The stomach
ends abruptly at the pyloric sphincter, a marked constriction beyond which the digestive
tract continues as the long, coiled small intestine, followed by the short, straight large
intestine. The mesentery supports the small intestine. Spread apart the coils of the small
intestine to observe it.
The first loop of the small intestine is the duodenum. Several organs and vessels lie in
this region, but may be difficult to discern. The pancreas lies along the duodenum. To
help identify it, pull the stomach to the left and reflect the liver to the right to expose its
dorsal surface. The pancreas is irregular, but note that part of it extends anteriorly toward
the spleen.
Observe the long, thin transparent lung lying dorsal to the stomach. The right lung is
similar in form. Look between the stomach and liver. You should discern the left and
right lungs. The liver is supported anterodorsally by the hepatocavoplumonary ligament.
The posterior vena cava is the large vessel passing through the posterior end of this
ligament.
Next, reflect the stomach to the right, so it lies on the liver’s dorsal surface. Note the
relationship among the liver, stomach, spleen, and pancreas, as well as their associated
mesenteries. Let the viscera fall back in place, and then reflect the liver to the left.
Examine the posterodorsal part of the liver for the gall bladder, a thin, translucent
greenish sac. Gently lift it and examine the region where it attaches to the liver.
Urinary and reproductive structures should be examined next. Lift the coils of the small
intestine in the posterior part of the peritoneal cavity to locate one of the paired gonads.
In males the testis is an elongated organ posteriorly in the pleuroperitoneal cavity lying
ventral to the kidney. The kidney, longer than the testis, is considerably wider posteriorly
than anteriorly. Its narrow anterior part is genital in function, while the wider posterior
portion is urinary.
In females the elongated ovary may be quite large. The presence of numerous eggs
within follicles gives the ovary a lobulated or granular appearance, in contrast to the more
regular surface of the testes. The follicles and eggs vary in size depending on their stage
of maturity, being quite large in some specimens and smaller in others.
Heart
The pericardial cavity lies just anterior to the liver. It is enclosed by the pericardial sac
and contains the heart. Continue the midventral incision of the abdominal wall
anteriorly, cutting through the coracoid cartilage, to expose the pericardial cavity. In
doing so you will also cut through the transverse septum, the partition separating the
pericardial and pleuroperitoneal cavity. Do not injure the posterior vena cava, which
passes through the septum to reach the pericardial cavity. Carefully remove the
musculature ventral cavity. The largest and most conspicuous part of the heart is the
ventricle, which occupies the posteroventral part of the pericardial cavity. Lift the
posterior end of the ventricle to observe the sinus venosus. The atrium lies anterodorsal
to the ventricle and is partially divided into left and right atria. The conus arteriosus is
the narrow tube extending anteriorly between the atria from the right side to the ventricle.