(_a_) The heart lying in the thin pericardium, the two auricles, the
single ventricle, the truncus arteriosus which divides into two
branches.
Remove the pericardium from the heart, and tilt the apex of the
heart forwards, noting the sinus venosus into which the right and
the left superior venæ cavæ (or precavals) and the single inferior
vena cava (or postcaval) open.
(_b_) The veins passing from each side of the sinus venosus. Each
superior vena cava is joined by the following branches:--
(i) The external jugular vein from the region of the tongue and
the mandible.
(ii) The internal jugular vein from the head and a thick
subscapular vein from the shoulder. These veins join the
superior vena cava independently of each other so that there is
no innominate vein as in the Frog.
(iii) The subclavian vein, made up of a brachial vein from the
arm, a cutaneous vein from the skin, and a muscular vein from
the abdominal muscles. The cutaneous and the muscular veins are
separate veins so that there is no single musculo-cutaneous
vein.
[_In the Frog the superior vena cava is joined by the following
branches_:--
(_i_) _The external jugular vein, formed by the union of a
lingual vein from the tongue and a mandibular vein from the
margin of the lower jaw._
(_ii_) _The internal jugular vein from the head and the
subscapular vein from the back of the arm and shoulder, both
joining the superior vena cava by a common vein, the innominate._
(_iii_) _The subclavian vein, formed by the brachial vein from
the fore-limb and a musculo-cutaneous vein from the muscles of
the body and from the skin._]
(_c_) The hypoglossal and the glossopharyngeal nerves, both running
alongside of the lingual artery.
Make an enlarged drawing showing the above parts (_a_) and (_b_).
2. Note the inferior vena cava, receiving the renal veins from the
kidneys, the hepatic veins from the liver, and opening into the sinus
venosus.
3. Trace back the abdominal vein, and note that it is formed by the
union of the two pelvic veins, which pass along the bases of the
legs. The pelvic veins occur deep down in the body under the
posterior part of the pelvic girdle, which should be cut through in
order to see them. At the union of the pelvic veins to form the
abdominal vein a small rectal vein, passing along the ventral surface
of the rectum, joins the abdominal vein.
In order to make out the femoral and the sciatic veins, turn the
Platana over and remove the skin from the back of the leg. The
femoral vein may then be seen lying on the surface of the leg,
between two of the muscles. By carefully separating these muscles the
whole of the femoral vein may be exposed. Deeper down in the muscles
of the leg lies the sciatic vein, and, between the sciatic and the
femoral veins, the internal iliac artery may be seen running
alongside of the sciatic nerve.
Trace the femoral and the sciatic veins forward, and note that they
join together at the point where they meet the pelvic veins and then
run forward to the kidney as the renal portal vein on each side.
Turn the Platana over again on to its back and note the renal portal
vein from the ventral side. Joining the renal portal vein is a large
vein formed of two branches. The one branch arises in the abdominal
wall, while the other passes along the base of the leg and joins the
abdominal vein. On each side three dorso-lumbar veins join the renal
portal vein.
[Illustration: FIG. 6.--Venous System of Xenopus and Rana.]
[_In the Frog the abdominal vein is also formed by the union of the
two pelvic veins. The pelvic veins, however, lie more superficially
than in the Platana. The femoral vein which passes along the front of
the thigh divides into two branches, the one branch forming the
pelvic vein, the other, joined by the sciatic vein from the muscles
and skin of the back of the thigh, forming the renal portal vein
extending along the outer side of the kidney. The dorso-lumbar vein
from the dorsal wall of the body joins the renal portal vein._]
Make a drawing showing the above parts.
B. Arterial System.
Distend the œsophagus with a piece of cotton wool or paper to show
the blood vessels more clearly. Trace out the anterior part of the
arterial system, made up of two branches of the truncus arteriosus
each of which divides into:--
(_a_) The carotid arch passing to the head region.
(_b_) The systemic arch curving round the œsophagus.
(_c_) The pulmo-cutaneous arch to the lungs and the skin.
_Fourth day._
=Arterial System= (_continued_).