The inferior vena cava (Fig. 126, _a_) is formed at about the level of
the last lumbar vertebra by the union of the two =common iliac= veins
(Fig. 126, _w_). It passes craniad near the dorsal median line, lying at
first dorsad of the aorta (_b_), then to the right, then ventrad. It
enters the substance of the liver in the dorsal part of the caudate lobe
of the latter, passes through the liver, and then through the diaphragm
near the ventrolateral edge of the central tendon. It passes then
craniad in the thoracic cavity (Fig. 129, _c_) ventrad of the caudal
lobe of the right lung, and enters the right auricle.
It receives the following branches (Fig. 126): =lumbar=, =iliolumbalis=
(_v_), =spermatica interna= (_u_), =renal= (_t_), =adrenolumbalis=
(_s_), =phrenic=, and =hepatic= veins. All but the last two named
accompany the arteries of the same name.
=V. phrenica.=--The phrenic veins gather the blood from the diaphragm
and empty into the vena cava as it penetrates the diaphragm.
=V. hepatica.=--The hepatic veins vary in number. They gather the blood
from the liver (sent in by the portal vein and hepatic arteries) and
enter the vena cava just caudad of the diaphragm.
VENA PORTÆ. THE PORTAL VEIN (Fig. 131).--The =portal= vein is the large
vein carrying the blood from the abdominal viscera to the liver. Within
the liver the portal vein breaks up into capillaries; these collect to
form the =hepatic= veins, which enter the vena cava inferior. The portal
vein (_a_) is formed near the pyloric end of the stomach (1) by the
union of the =superior mesenteric= (_b_) and =gastrosplenic= (_c_) veins
and passes thence along the ventral border of the foramen epiploicum
(foramen of Winslow) to the liver (2), where it divides, going to the
lobes of the liver. On its way to the liver it may receive the
=pancreaticoduodenalis= (_d_), =gastroepiploica= (_e_), and =coronaria
ventriculi= (_f_). These may unite with the portal separately, or any
two or all three may unite to form a single trunk before entering the
portal vein.
1. =V. coronaria ventriculi= (_f_) gathers the blood from the lesser
curvature of the stomach and anastomoses with the gastrosplenic veins.
It usually empties into the portal vein near the pylorus.
2. =V. pancreaticoduodenalis= (_d_) receives the blood from the pancreas
and first part of the duodenum, and empties into the vena portæ near to
or with the preceding.
[Illustration: FIG. 132.--PORTAL VEIN.
_a_, portal vein; _b_, superior mesenteric; _c_, gastrosplenic; _d_,
pancreaticoduodenalis; _e_, gastroepiploica; _f_, coronaria
ventriculi; _g_, _h_, _i_, branches of gastrosplenic; _j_, inferior
mesenteric. 1, stomach; 2, liver; 3, duodenum; 4, spleen.]
3. =V. gastroepiploica= (_e_) comes from the greater curvature of the
stomach and ascending limb of the great omentum. It empties into the
vena portæ ventrodextrad of the opening of the coronaria ventriculi, or
sometimes in common with it.
4. =V. gastrolienalis= (_c_).--The gastrosplenic is one of the veins
which unite to make up the portal vein. It is formed by three branches:
one (_g_) from the horizontal or gastric portion of the pancreas, one
(_h_) from the stomach and gastric end of the spleen, the third and
largest (_i_) from the caudal end of the spleen and descending limb of
the great omentum. The three branches unite and the common trunk joins
the superior mesenteric vein (_b_) to form the portal vein as above
described.
5. =V. mesenterica superior= (_b_).--The superior mesenteric vein
receives the blood from the small and large intestines. It is formed by
numerous branches which follow and have the same name as the
corresponding arteries. It receives also the =inferior mesenteric= (_j_)
from the large intestine. The numerous branches unite, and the main
trunk thus formed joins the gastrosplenic (_c_), and the two united
become the portal vein (_a_).
VENA ILIACA COMMUNIS. COMMON ILIAC VEIN (Fig. 126, _w_; Fig. 127, page
310).
The common iliac veins (Fig. 126, _w_) are the two large vessels which
unite in the sacral region to form the inferior vena cava (_a_). Each is
a large vessel, usually four or five centimeters in length, which is
formed by the junction of the large =external iliac= vein with the
smaller =hypogastric= vein (_z_). The left common iliac usually receives
the =V. sacralis media= (_o_); other lateral branches are as a rule not
received by the common iliac veins.
There is much variation as to the formation of the common iliac veins
and their union to form the vena cava. On this subject the paper by
McClure, in the _American Naturalist_, vol. XXXIV. pp. 135-198 (March,
1900), may be consulted with profit. The more typical variations may be
classified as follows: (1) The two common iliac veins may be longer than
usual, so that the vena cava is formed farther craniad than usual. (2)
There may be in the abdominal region two separate veins (=venæ
cardinales=) representing the inferior vena cava, these uniting in the
region of the kidneys. (3) The vena sacralis media may enter into the
left common iliac (the usual condition); or the right common iliac (as
in Fig. 126); or it may fork, one branch passing to the left, the other
to the right common iliac.
Branches of the common iliac veins:
1. =V. sacralis media= (Fig. 126, _o_).--This follows the course of the
corresponding artery and usually enters the left common iliac.
2. =V. hypogastrica= (or =iliaca interna=) (_z_).--The hypogastric or
internal iliac vein joins the medial side of the external iliac to form
the common iliac (_w_). Its branches follow the branches of the
corresponding artery except that the vein from the bladder (umbilical
vein) joins the =V. hemorrhoidalis media=. Also the =vena glutea
inferior= receives a large superficial communicating branch (Fig. 163,
_k_′) from the =vena saphena parva=. This branch leaves the saphena
parva (Fig. 163, _k_) at the popliteal space, and passes over the
lateral surface of the biceps muscle to its proximal end. Here it passes
between the biceps and caudofemoralis to join the vena glutea inferior.
3. =V. iliaca externa= (Fig. 127, page 310).--This vein follows the
corresponding artery, collecting the blood from the posterior extremity.
Its branches are the same and have in general the same distribution as
those of the artery. The vein has, however, certain branches in addition
to those of the artery, resulting in a somewhat different general
arrangement of vessels; it will be necessary therefore to give an
account of the system of veins from the foot and lower leg.
The blood is collected from the foot into two sets of veins which may be
distinguished as the _deep_ and the _superficial_ sets. The veins of the
deep set are those which accompany the branches of the popliteal and
anterior tibial arteries. Those of the superficial set are larger and
carry most of the blood. On the dorsum of the foot blood is collected
from the third, fourth, and fifth digits by two or three superficial
metatarsal veins, which unite opposite the proximal end of the
metatarsus into a single vein. This receives a similar branch coming
from the dorsum of the second digit, and has numerous branches in the
ankle region which form here a network, communicating with the vena
saphena parva (Fig. 163, _k_), and with branches from the plantar side
of the foot. From this network two or three main veins pass proximad on
the medial side of the leg, along with the branches of the arteria
saphena, and unite with a similar vein from the plantar side of the foot
to form the vena =saphena magna= (Fig. 127, _k_, page 310), which
accompanies the arteria saphena to join the femoral vein (_a_).
On the plantar side of the foot small veins pass from the digits to a
superficial =venous plantar arch=, which lies just proximad of the
fibrous pad on the sole of the foot. At its medial side this arch
extends proximad and dorsad to join that branch of the vena saphena
magna which comes from the dorsum of the second digit. On the lateral
side it extends proximad along the lateral margin of the foot, sends a
communicating branch dorsad to the branches of the V. saphena magna, and
continues along the lateral border of the foot to the ankle. It forms
the beginning of the =V. saphena parva= (Fig. 163, _k_, page 401). This
receives branches from the lateral surface of the ankle, which
anastomose with those of the saphena magna. The saphena parva then
passes proximad along the lateral surface of the leg, close to its
ventral border, to the popliteal space. At the distal end of the
popliteal space it divides into two branches. One passes inward through
the fat of the popliteal space, receiving branches from the lymphatic
gland situated here, and joins the popliteal vein. The other (_k_′)
remains superficial and continues proximad over the lateral surface of
the biceps to the proximal end of that muscle. Here it passes between
the biceps and caudofemoralis to join the inferior gluteal vein.