reach the posterior lacerated foramina, through which they 'pass
to form the beginning of the internal jugular veins. Most of the
blood from the base of the brain passes into the cavernous sinuses
which lie in the middle cranial fossa, one on each side of the pituitary
fossa. These receive the ophthalmic veins from the orbit in front
and-, after running backward, for about an inch, divide into the
superior and inferior petrosal sinuses, the former of which joins the
ateral sinus within the cranium, but the latter runs to the posterior
lacerated foramen, after passing through which it joins the lateral
sinus, which is now becoming the internal' jugular vein;
The internal 'ugular vein (fig. 5, I.];.) thus formed runs down at
first behind and, then to the outer side: of the internal and common
carotid arteries and at the root of the neck joins the subclavian vein
of its own side to form the in nominate vein. In its course downthe
neck it receives the common facial vein already -mentioned, as well
as tributaries from the ton e, harynx, larynx and thyroid body;
The deep veins of the heaciu audi face tend to form plexuses rather
than venae comites; of these, pleriygoid, deep temporal, pharyngeal
and .rub occipital plexuses are recogn zed.
Veins of the Upper Extremity.—On the dorsumof the hand and in front of the wrist superficial venous plexuses are easily seen through the skin. From these the blood passes up the forearm chiefly on its fiexor surface b the radial, median and anterior and posterior ulna veins. just belbw the bend of the elbow 'the median vein communicates with the deep veins and then divides into two branches like the limbs of a v . Of these the inner is the median basilic and is noticeable as the vein from which patients were usually bled, while the outer is the median cephalic. After a course of an inch or two the median basilic is joine by the anterior and posterior ulnar veins and the median cephalic by the radial. After thlsjunction the median basilic is continued up the inner side of the arm asthe basilu: which pierces the deep fascia about the middle of the arm and in the axilla ]oins the venae comites of the brachial artery to form the axillary vein, which lies on the inner side of its artery. The median cephalic vein after joining the radial runs up the outer side of the arm as the cephalic and a little below the cavicle passes through the custocoracoid membrane toenter the upper part of the axillary vein. At the outer border of the first rib the axillargevein becomes the subclavian (fig. 5, S.), which lies in front of and low its artery and is separated from it by the scalenuslanticus muscle. Thearrangement of the superficial veins, especially in front of the elbow, is liable to great variation and often differs on the right and left sides of the same body.
Veins of the Lower Extremity.-The superficial veins of the lower extremity begin in a venous arch on the dorsum of the foot. From the inner extremity of this the internal saphenous vein runs up, in front of the inner ankle along the inner side of the leg, and, passing behind the inner side of the knee, continues up the thigh, gradually working forward until it reaches the saphenous opening in the deep fascia of the thigh a little below the spine of t pubis. Here it pierces the deep fascia (fascia lata) to enter the common femoral vein. In this long course it has many valves and receives numerous tributaries, one of which, the saphenous collateral, runs up nearly parallel to it and on its outer side and joins it just below the saphenous opening. From the inner end of the dorsal arch of the foot the external saphenous vein runs up behind the outer, ankle along the mid line of the calf to pierce the deep fascia in the popliteal space behind the knee to open into the popliteal vein- Among the deep veins venae comites are found until the popliteal artery is reached, while above this superficial, deep and common femoral vein; accompany their respective arteries. n the groin the ' common femoral vein lies on the inner side of its artery. Veins of the Abdomen.-The common femoral vein, after passing deep to Poupart's ligament, becomes the external iliac (fig. 5, E.I. which runs along the brim of the true 'pelvis and, after a course of some three inches, joins the internal iliac (fig. 5, I.I.) which drains the pelvis and so forms the common iliac vein. In front of the body of the fifth lumbar vertebra the common iliac veins of the two. sides unite .to form the inferior vena cava (fig. 5, I.V.C.), a very large trunk which runs up on the right of the abdominal aorta to an opening in the diaphragm (q.v.). On its way it receives spermatic or ovarian veins from the genital glands, renal vein; (fig.d5, R.V.) from the kidneys, and lumbar veins (fig. 5, L.V.) from the abdominal walls. Before reaching the diaphragm it lies in a groove in the back of the liver (q.v.) and receives, the hepatic veins from that organ. The hepatic portal system which lies in the abdomen will be treated later. Veins of the Thorax.-The inferior vena cava, after piercing the diaphragm, has a very short thoracic course, and opens into the lower and back part of the right auricle of, the heart (q.v.). The right and left in nominate veins lg, R.§ I., and L.I.) are formed behind the sternal end of the clavicle by the union of the subclavian and internal jugulars of their own side. The left vein is much longer than the right and runs nearly horizontally behind the upper bali of the manubrium sterni to join its, fell'ow on therilght side, of that bone just below the, first rib. By the gunction o these the
- uierior venacava. (fig. 5, S.V.C.) is formed, , w ich runs down to the
rig t auricle of the' cart; The chief tributaries of, the in nominate veins are the vertebral, the internal mammary and the ingerior thyroid. The intercostal veins open into the aaygos veins, whic begin in the abdomen sometimes by a 'vertical trunk joining, the, lumbpr veins known as the ascending lumbar, sometimes on the right side by a communication with the inferior vena cava. ' The right azygos vein is known as the vena azygas major (fig. E A.M'.) and passes through theYaortic opening, of the diaphragm. =ntering the thorax, it runs nip in front of the thoracic vertebrae, to the right of the aorta and toracic duct, and receives the intercostal veins pf the right side, At the level of the fourth thoracic vertebra it arches forward to open into the posterior'surface of the superior vena cava. ' On the left side, the up r intercosta veinsjointo form 'the left superior intercostnl vein 5, L, S.I.), .which opens into-the-left in nominate. Lower downpthe intercostal veins from the fourth to the seventh spaces form the superior hemiazygos vein or hemiazygps accessoria (fig. '5, H.A.), which 'runs down on the left of the spinal column and, crossing it about the level of the ei hth or ninth thoracic vertebra, opens into the vena az gos major. gfhe lower intercostal veins on the left side join the in erior hemiazygos vein (fig. 5, H.V.), which runs up and olpens either into the superior hemiazygos or into the' azygos maipr be ow the opening of that vein. " Pulmonary erwns System.-The veins emerging from the lungs bring back the oxygenated blood from those organs to the lleft ventricle of the heart and also the greater art, if not all, of, theblood carried b the bronchial arteries to nourish the lungs. The existence of bronchial veins is asserted, but they are extremely difficult to demonstrate, and if present are quite incapable of returnin all the blood which the bronchial arteries car? to thelungs. There are three, pulmonary veins{ coming out of the right lung, while on the left there, are only two. On the right side(however, two of the three veins usually unite in the root of the lung, so that there are as a rule -two pulmonary veins entering the left auricle of the heart on each side, but it is not uncommon to find three' on the ri ht side or one on the left. The pulmonary veins have no valves ami return the blood carried to the lungs by the ulmonary arteries as well as most, ifnot all, of that carried by the 'bronchial arteriesQ Hepatic Portal System.-The veins which drain the blood from the stomach, intestines, Zpleen and pancreas unite to form-aflarge vein, which beginsbehin, the head of the pancreas:and ends(by dividin into right andleft branches in the transverse fissure of the liver. gfhis is the 'pirtal vein which'lies in front of the inferior vena cava and is a ut-three inches long. Its' formative tributaries are the superior and inferiormesentericand the splenic veins: These accompany the arteries of the same inamepand their most usual method of termination is that the inferior mesenteric runs up and joins 'the splenic to the left of the middle line of the body, and this, after running' horizontally' to a point a little to the right of-the middle -line, § oinsthé'superior mesenteric, and so the portal vein is formed. ° There are two marked characteristics of the portal system; one is that it has no valves and the other that it begins and ends in capillaries, since the two terminal 'branches of' the 'portal', vein branch and rebranch in 'a manner already described 'in'the article LINER; In the lower part of the- rectum the veins run partly into the portal and partly into the general system, and in this de ndent; position they are liable to become varioosex and to form iiiemorrhoids or piles;
The histology of the' veins corresponds very closely to'that of the arteries (q.v.).-; their walls are, however, much thinner and there is less muscular and elastic tissue. At certain places, especially where tributaries come in, the endothelial linin is raised to form semi lunar pocket-like valves. In most cases tgere are two cusps to each valve, but three or one are sometimes found. Theopening of the pocket is of course arranged so that it shall only be hlled when there is a tendency to regurgitation of the blood., g Embryology,
° A The vitelline or omphalo-mesenteric veins, returning the blood from the yolk- sac, are the first to appear, and later on, with the formation oéjtheplacenta, the umbilica veins develop. Both these open into 1; e hinder, (caudal) part of the heart, which is already being con-1
While this is going on the veins from the different body segments are' received into two, longitudinal, »
trunks on each side, the anterior P -l' P
(cephalic) of which is the primitive
s.v. .C Sw .c
stricted off as the sinus venosus (see fig
ju ular or anterior cardinal (fig. 1,
Pi), and the posterior' (caudal), the
posterior cardinal for fsimply cardinal' , L
ve<ing(§ g. 1, P.C.). =As-the, heart is », ,
arf first situated in the region which-, S V
will laterbe 'the neck bf the embryo, V.V. ' "
the “primitive jugular receives very K
few segmental vemsand the cardinal very
many. These twc trunks .join V »U.V, ,
one another on each side and, open . P- -, P¢Cinto the side of the sinus venosus (S.V.) Fig”,
by a transverse communication which ,
is called the duct of Cuvier (D.C.). The condition of the -venous system at this, stage is shown in the accompanying diagram (fig. 15). 5, ~, .
As the vitelline veins run from the yolk 'sac to the heart along
