the ventricle occurs, the
increased, tension of the blood only closes the aperture the tighter,
and the current passes on into the aorta, where we find three
watch-pocket valves, with the pocket turned away from the heart,
which are also closed and tightened by any attempt at regurgitation
(back-flow). A similar process occurs on the right side of the heart,
but here, instead of a mitral valve of two flaps between auricle and
ventricle, we have a tricuspid valve with three. The thickness of the
muscular walls, in view of the lesser distance through which it has to
force the blood, -are- [is] less for the right ventricle than the left.

Section 45. The following are the chief branches of the aorta. The
student should be able to follow them with certainty in dissection;
they are all displayed in the Figure; but it must not be imagined for a
moment that familiarity with this diagram will obviate the necessity
for the practical work; (in.) is the innominate artery; it forks into
(s.cl.a.) the right subclavian, and (r.c.c.) the right common carotid.
Each carotid splits at the angle of the jaw into an internal and an
external branch. The left common carotid, (l.c.c.) arises from the
base of the innominate,* (l.s.cl.a.) the left subclavian, directly from
the aorta. The aorta now curves round to the dorsal middle line, and
runs down as seen in Figure 1, Sheet 1 (d.ao.) and Figure 1, Sheet
2 (d.ao.). Small branches are given off to the ribs, and then comes
the median coeliac (coe.a.) to the stomach and spleen, the median
superior mesenteric (s.mes.a.) to the main portion of the intestine,
and the inferior mesenteric (p.m.a.) to the rectum. Note that no veins
to the inferior vena cava correspond to these arteries-- the blood they
supply going back by the portal vein (p.v.). The paired renal arteries
(r.a.) supply the kidneys, and the common iliacs (c.il.a.) the hind
legs, splitting into the internal iliacs (i.il.a.) and the femoral (f.).

{Lines from Second Edition only.}
[The student should note that the only arteries in the middle line
are those supplying the alimentary canal.]

{Lines from First Edition only.}
* -The figure is inaccurate, and represents the left common carotid
as arising from the aortic arch.-

Section 46. The distribution of the veins of the rabbit has only a
superficial parallelism with arteries. The chief factors of vena cava
inferior are the hepatic vein (h.v.), which receives the