The superior vena cava is the great vein returning the blood from the
head, fore-limb, and cranial part of the trunk. It extends from the
level of the first rib on the right side of the vertebral column to the
right auricle. Its caudal end lies dorsad of the aortic arch. Opposite
the right rib it is formed by the junction of the two innominate veins
(_m_).
Branches of the superior vena cava:
1. =V. azygos= (_d_).--The first branch of the superior vena cava is the
azygos vein, which enters the vena cava on the right side a centimeter
or less craniad of the root of the right lung. It is formed in the
abdominal cavity by the confluence of two or three small veins, which
collect the blood from the muscles of the dorsal wall of the abdomen.
The small median trunk thus formed enters the thoracic cavity between
the crura of the diaphragm and lies on the ventral surface of the centra
of the thoracic vertebræ, slightly to the right of the middle line. The
azygos receives the =intercostal= veins (_n_), which correspond to the
intercostal arteries and have the same course and distribution. In the
caudal part of the thoracic cavity the intercostals enter the azygos
separately, but the intercostals of the cranial intercostal spaces
usually unite two or three together and enter the azygos by one or more
common trunks. The azygos also receives =bronchial= and =œsophageal=
veins, corresponding to the similarly named arteries.
[Illustration: FIG. 129.--THORACIC BLOOD-VESSELS, FROM THE RIGHT SIDE.
_a_, aorta; _b_, vena cava superior; _c_, vena cava inferior; _d_, V.
azygos; _e_, A. subclavia dextra; _f_, A. mammaria interna; _g_, V.
mammaria interna; _h_, costocervical axis; _i_, united trunk of
vertebral and costocervical veins; _j_, A. and V. axillaris; _k_, V.
jugularis externa; _l_, V. jugularis interna; _m_, the two innominate
veins; _n_, intercostal arteries and veins; _o_, thyrocervical axis.
1, heart; 2, trachea; 3, œsophagus; _I_-_XI_, cut ends of the first
eleven ribs.]
2. =V. mammaria interna= (_g_).--The internal mammary veins follow the
corresponding arteries. The two veins unite to form a common trunk
which, after receiving a branch from the cranial part of the sternum,
enters the vena cava opposite the third rib.
3. =Vv. anonymæ= (Fig. 129, _m_; Fig. 115, _p_).--The innominate veins
unite opposite the first intercostal space to form the vena cava
superior. Each extends from the cranial end of the vena cava superior
craniolaterad to a point a short distance craniad of the first rib and
is there formed by the union of the =external jugular= (Fig. 129, _k_)
and =subclavian= (_j_) veins. The innominate vein has the following
branches:
A and B. =Vv. vertebralis= and =costocervicalis= (_i_).--The vertebral
and costocervical veins unite to form a single trunk which enters the
innominate about opposite the first rib. These two veins follow the
corresponding arteries. (Sometimes the vertebral and costocervical veins
enter the innominate separately, and in other cases one or more of the
components of the costocervical veins (e.g., the transversa colli) may
enter the axillary vein. In other cases the entire common trunk of the
vertebralis and costocervicalis may enter the superior vena cava
directly.)
C. =V. subclavia.=--The subclavian vein enters the innominate at about
the level of the first rib. Outside of the thorax it is called the
axillary vein (_j_); this comes from the arm.
[Illustration: FIG. 130.
SUPERFICIAL ARTERIES, VEINS, AND NERVES ON THE EXTENSOR SIDE OF THE
ARM AND DORSUM OF THE HAND.
_a_, V. cephalica; _b_, V. mediana cubiti; _c_, V. cephalica
antibrachii; _d_, A. collateralis radialis superior; _e_, Aa. and Vv.
digitales dorsales; _f_, A. radialis; _g_, superficial radial nerve;
_h_, N. musculocutaneus; _i_, N. cutaneus medialis.]
=Veins of the Arm.=--The blood is returned from the arm by two systems
of veins,--a deep and a superficial system.
The deep system is composed of veins which correspond to the branches of
the axillary artery, follow in general the same course, and receive the
same names (Fig. 122). They unite to form the axillary vein. The
brachial vein does not pass with the brachial artery through the
supracondyloid foramen.
The superficial system comprises the vena cephalica and its branches.
=V. cephalica= (Fig. 130).--Several superficial branches lying in the
palm of the hand unite to form a common trunk which curves about the
radial side of the wrist and here unites with a similarly formed trunk
from the dorsum of the hand. The vein formed by this union, vena
cephalica (antibrachii) (_c_), passes to the elbow accompanying the
radial nerve (_g_) and the collateral radial artery (_d_), and lying on
the extensor carpi radialis longus muscle just beneath the integument.
It receives small lateral superficial branches. At the elbow it divides
into two: these are the vena cephalica (humeri) (_a_) and the =vena
mediana cubiti= (_b_). The latter passes beneath the pectoantibrachialis
muscle, across the biceps, and unites with the brachial vein in the
concavity of the elbow.
The vena cephalica (humeri) passes at the elbow onto the upper arm,
following the lateral border of the clavobrachial muscle. It thus
reaches the acromiodeltoid muscle, where it divides into two branches.
One passes inward beneath the acromiodeltoid, and joins the vena
circumflexa posterior (a branch of the axillary). The second continues
over the outer surface of the shoulder, and finally joins the vena
transversa scapulæ (a branch of the external jugular).
D. =V. jugularis externa= (Fig. 131; Fig. 65, 5, page 109).--The
external jugular vein comes from the head and face. It is formed by the
junction of the anterior (Fig. 131, _c_) and posterior (_b_) facial
veins near the ventral border of the sternomastoid muscle. It passes
thence obliquely across the sternomastoid to the triangular interval
between it and the clavotrapezius. In the interval it receives a small
branch which accompanies the branch of the transversa scapulæ artery to
the clavobrachialis muscle, receives next the common trunk of the vena
cephalica and transversa scapulæ, and opposite the cranial end of the
manubrium receives the internal jugular vein (Fig. 129, _l_). It then
unites with the subclavian to form the innominate vein. Near the point
where it receives the internal jugular the external jugular vein
receives the =thoracic duct= (Fig. 118, 5).
Branches of the external jugular:
_a._ =V. transversa scapulæ.=--This follows the course of the artery of
the same name. One of its branches receives one of the two terminal
divisions of the vena cephalica (q. v.). In many cases veins which
correspond to branches of the transversa scapulæ artery enter the
external jugular separately (as shown in Fig. 118, _x_ and _y_).
_b._ =V. cervicalis ascendens.=--A small branch which follows the
corresponding branch of the thyrocervical axis.
_c._ =V. jugularis interna= (Fig. 118, 2; Fig. 119, page 284).--The
internal jugular vein varies much in size and in the place where it
joins the external jugular. The point of junction is usually at about
the level of the first rib, but may be much farther craniad. It arises
on the ventral side of the basal portion of the occipital by the
junction of a number of veins which are described below. The internal
jugular passes caudad in the neck region at the side of the trachea, in
company with the common carotid artery and the vagus and sympathetic
nerves. In this region it receives branches which accompany the branches
of the common carotid artery.
The veins which by their union form the internal jugular vein are the
following:
(1) One or two veins from the venous sinuses of the brain, leaving the
cranial cavity by the jugular foramen. These are described in the
account of the veins of the brain.
(2) A large communicating branch from the posterior facial.
(3) The =vena occipitalis=, a large branch coming from the vertebral
column (which it leaves by the atlantal foramen) and from the back of
the head.
_d._ =V. facialis anterior= (Fig. 131, _c_).--The anterior facial vein
collects the blood from the face, the tongue, and adjacent parts; it
joins the =posterior facial= (_b_) caudad of the angle of the jaw to
form the external jugular vein.
The anterior facial begins over the frontal bone caudad of the orbit,
where it is known as the =frontal= vein (_c″_). This runs along the
dorsal border of the orbit, into which it dips. It sends a communicating
branch into the orbit, and receives small veins (=superior palpebral=)
from the upper eyelid. It then turns ventrad, passing along the cranial
angle of the eye between the levator labii superioris proprius (5) and
the orbicularis oculi (8) muscles, being called in this region the
=angular vein= (_c′_). This receives branches (=external nasal veins=,
_k_) from the side of the nose. The vein crosses the malar bone
obliquely (now receiving the name =anterior facial=, _c_) and follows
the cranioventral border of the masseter muscle (9). As it passes the
infraorbital foramen it receives through the foramen a small vein from
within the orbit. It receives also the =inferior palpebral= (_j_) from
the lower eyelid, and the =superior labial= vein (_i_) from the upper
lip. Just caudad of the angle of the mouth it receives from beneath the
cranioventral margin of the masseter the =V. facialis profunda= (_h_)
described below. Still farther caudad it receives the =inferior labial=
vein (_g_) from the lower lip, and a small branch from the masseter
muscle. Caudad of the middle of the cranioventral border of the masseter
it receives from beneath the lymphatic gland of this region the large
=submental= vein (_f_). Next the anterior facial vein receives a large
communicating branch (=V. transversa=, _d_) which passes transversely
across the ventral surface of the throat and connects the two anterior
facial veins of the opposite sides. From the middle of this
communicating branch an unpaired trunk passes caudad in the middle line
and divides into the two =laryngeal= veins, which pass to the larynx; a
small branch is continued from the unpaired trunk craniad into the
tongue. The communicating branch receives also near its junction with
the anterior facial a rather large superficial branch (_e_) which comes
from the sides of the lower jaw and passes across the lymphatic gland
(12) to join the communicating branch.
[Illustration: FIG. 131.--SUPERFICIAL VEINS AND ARTERIES OF THE FACE.
_a_, external jugular vein; _b_, posterior facial vein; _c_, anterior
facial vein (_c′_, angular vein; _c″_, frontal vein); _d_,
communicating branch with opposite anterior facial; _e_, superficial
branch from lower jaw; _f_, submental vein; _g_, inferior labial vein;
_h_, deep facial vein; _i_, superior labial vein; _j_, inferior
palpebral vein; _k_, external nasal veins; _l_, posterior auricular
vein; _m_, superficial temporal vein; _n_, anterior auricular vein;
_o_, external maxillary artery; _p_, inferior labial artery; _q_,
superior labial artery; _r_, infraorbital arteries; _s_, superficial
temporal artery; _u_, anterior auricular branch of posterior auricular
artery. 1, M. adductor auris superior; 2, M. corrugator supercilii
medialis; 3, M. corrugator supercilii lateralis; 4, M. levator labii
superioris alæque nasi; 5, M. levator labii superioris proprius; 6, M.
myrtiformis; 7, M. orbicularis oris; 8, M. orbicularis oculi; 9, M.
masseter; 10, parotid gland; 11, submaxillary gland; 12, lymphatic
glands.]
The following larger branches of the anterior facial are not described
above:
=V. facialis profunda= (Fig. 131, _h_).--The deep facial vein enters the
anterior facial from beneath the masseter, just caudad of the angle of
the mouth. It collects branches from the soft and hard palates and the
teeth, these branches passing along with the corresponding arteries for
a distance, then uniting and passing ventrolaterad beneath the zygomatic
arch to join the anterior facial. The deep facial vein also receives
branches which come from the venous plexus that lies in the same region
as the arterial carotid plexus.
=V. submentalis= (Fig. 131, _f_).--This enters the anterior facial vein
at the ventral border of the masseter muscle and near the cranial end of
the two superficial lymph-glands (12) in this region. The submental vein
is formed at the dorsal border of the digastric muscle by two branches
emerging from between the digastric and the mandible. The more cranial
of these, =V. lingualis=, collects branches from the tongue, from its
middle to the tip; it passes through the middle of the lateral border of
the mylohyoid muscle to join the other branch. The second branch emerges
from between the mandible and the pterygoid muscles. It comes from near
the caudal end of the mandible, where it becomes continuous with a
communicating branch from the posterior facial vein, and receives a
branch which comes from the mandibular canal; also small branches from
the adjacent parts.
_e._ =V. facialis posterior= (Fig. 131, _b_).--The posterior facial vein
arises from the region of the internal maxillary artery, its terminal
branches following the branches of the artery. It collects blood from
the pterygoid, masseter (9), and temporal muscles, and forms a plexus
which is interwoven with the carotid (arterial) plexus in the region of
the orbital fissure. It is connected with the submental vein by a
communicating branch. From the posterior facial a branch extends ventrad
close against the outer surface of the tympanic bulla and then turns
caudad, receives a branch from the pharynx, then continues to join the
internal jugular. The posterior facial itself passes laterad along the
caudal border of the masseter (9) and the ventral border of the parotid
gland (10), then becomes superficial and turns ventrad over the outer
surface of the submaxillary gland (11) to join the anterior facial (_c_)
caudad of the angle of the jaw.
As it passes ventrad of the parotid gland (10), just before becoming
superficial, the posterior facial receives the =superficial temporal=
(_m_). This at first follows the superficial temporal artery (_s_), then
enters the substance of the parotid gland, joining the posterior facial
near the ventral border of the latter. The superficial temporal receives
the =anterior auricular= (_n_), a large vein passing along the cranial
border of the auricular opening and arising dorsad of the eye.
The posterior facial receives also, at the point where it passes from
beneath the parotid gland, the =posterior auricular= or =great
auricular= vein (_l_). This collects blood from the back of the head and
the external ear, its branches following those of the artery of the same
name. It passes along the caudal border of the parotid gland to join the
posterior facial.
VEINS OF THE BRAIN AND SPINAL CORD.--The veins of the brain form a large
number of small vessels which pour their blood into larger veins lying
in folds of the dura mater; these are known as the =venous sinuses= of
the dura mater. These sinuses communicate with the venous plexus about
the orbital fissure, coming from the posterior facial vein; with the
internal jugular through the jugular foramen, and with the vertebral
veins, in the vertebral canal. The chief sinuses of the dura mater on
the dorsal side of the brain are as follows:
1. =Sinus sagittalis superior.=--This lies in the dorsal part of the
falx cerebri, between the two hemispheres of the cerebrum. It receives
veins from the dorsal and middle parts of the cerebrum, and passes
caudad to the tentorium. Here it enters the sinus transversus. It
receives the =vena cerebri magna=, a large vein coming from the interior
of the brain and passing directly dorsad at the caudal end of the corpus
callosum to enter the sinus sagittalis.
2. =Sinus transversus.=--This lies in a canal in the dorsal border of
the tentorium. It receives numerous small veins from the cerebellum,
roof of the skull, etc. One or two centimeters on each side of the
middle line the sinus transversus passes out of the canal onto the
caudal surface of the tentorium, thence proceeds caudoventrad obliquely
over the surface of the cerebellum, unites with veins from the ventral
side of the brain, leaves the skull by the jugular foramen, forming thus
the =inferior cerebral= vein, and joins the internal jugular vein.
On the ventral side of the brain are the following sinuses of the dura
mater:
3. =Sinus cavernosus.=--A short broad venous sinus, one on each side of
the hypophysis, on the body of the sphenoid. It receives veins from the
side and ventral surface of the brain. The two sinuses are connected by
communicating branches craniad and caudad of the hypophysis. From them
branches pass out through the orbital fissure to join the plexus formed
by the branches of the posterior facial vein.
4. =Sinus petrosus inferior.=--This arises from the sinus cavernosus and
passes caudolaterad in the groove between the edge of the petrous bone
and the basilar portion of the occipital. Reaching the jugular foramen
it divides; part joins the termination of the sinus transversus to form
the =inferior cerebral vein=, which passes through the jugular foramen
to join the internal jugular vein. The other portion of the sinus
petrosus inferior passes through the condyloid canal of the occipital
bone, communicates by a strong transverse branch across the surface of
the basioccipital with the vein of the opposite side, and enters the
spinal canal through the foramen magnum. Here it joins the sinus of the
vertebral column.
5. =Sinus columnæ vertebralis.=--On the ventral surface of the vertebral
canal, beneath the periosteum, are two wide venous sinuses, one on each
side of the middle line. These sinuses extend the entire length of the
spinal cord. At the atlantal foramen each sends a strong branch to the
internal jugular vein. Farther caudad they send branches to the
vertebral, intercostal, and lumbar veins, and communicate with each
other by numerous transverse branches. They receive many small veins
from the spinal cord.