Part 29

The veins of the body may be classified into three main groups: (1) the veins of the heart; (2) the superior vena cava and its branches; (3) the inferior vena cava and its branches. The portal system of veins will be considered with the inferior vena cava.

1. Veins of the Heart.

The veins of the heart consist of one large vein, the =vena cordis magna=, and a number of small veins.

=Vena cordis magna= (Fig. 118, 3).--This arises as a number of scattered branches on the surface of both ventricles. These unite to form two main trunks. One of these, on the ventral side of the heart, marks externally the septum between the two ventricles. It passes beneath the left auricular appendage, then turns to the left and passes along the sulcus coronarius to the dorsal side of the heart. Here it unites with the second main trunk which ramifies over the surface of the left ventricle. Arriving at the base of the right auricle it enters this by the coronary sinus, which lies just beneath the opening of the inferior vena cava.

In addition to the vena cordis magna and its branches there are a number of small veins, especially in the wall of the right ventricle. These enter the right auricle by a number of small separate openings along the sulcus coronarius.

2. =Vena cava superior= (Fig. 129, _b_).

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.

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.

=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.

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.

3. =Vena cava inferior= (Fig. 129, _c_; Fig. 126, _a_).

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.

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.