2. A. femoralis (Fig. 127).—This is the continuation of the external iliac onto the medial surface of the thigh. The artery lies in a triangular depression between the borders of the sartorius (1) and gracilis (9) muscles. The floor of the depression is formed by the adductor longus (6), pectineus (5), vastus internus, and rectus femoris (3) muscles. This triangular depression is known as the iliopectineal fossa, or Scarpa’s triangle; it contains also the femoral vein (a) and saphenous nerve (g), which pass along with the artery. The artery extends distad, and at about the middle of the length of the thigh it passes, along with the vein and nerve, into a groove between the vastus medialis and the adductor femoris. This groove is converted into a canal by the overlying aponeurosis; it is known as Hunter’s canal or the canalis adductorius. At the distal end of the adductor femoris the femoral artery ceases to be superficial and passes between the vastus medialis and the semimembranosus to the popliteal space; it now receives the name A. poplitea.

Branches of the femoral artery:

a. A. circumflexa femoris lateralis (Fig. 127, d).—The lateral circumflex arises from the femoral about one centimeter from its emergence from the abdominal cavity. It passes craniad and laterad and divides into two main portions. One part passes between the rectus femoris and vastus medialis, gives branches to these muscles, and sends an ascending branch to the structures about the hip-joint, and a descending branch into the vastus medialis muscle. The remainder of the lateral circumflex passes along the inner (lateral) surface of the sartorius (1) to the cranial border of the leg, giving branches to the sartorius (1) and tensor fasciæ latæ (2).

b. A large muscular branch (e) passes caudad (or ventrad) and distad across the distal end of the adductor femoris (7) and between the gracilis (9) and semimembranosus, supplying these muscles. Other small muscular branches may be given off from both sides of the femoral.

c. A. articularis genu suprema (h).—The superior articular artery arises from the femoral, either in common with the saphenous artery or separately, a little proximad of the point where the femoral ceases to be superficial. It passes toward the knee, between the vastus medialis and semimembranosus, and covered by the sartorius (1), and ramifies over the medial surface of the knee-joint and in the structures just proximad of the joint.

d. A. saphena (f).—The saphenous artery frequently takes origin in common with the superior articular (h), but may arise separately at about the same level. It passes distad across the gracilis (9), accompanied by the saphenous nerve (g) and vein, sends several branches dorsad (toward the knee), and at about the middle of the lower leg it divides into two main branches, a dorsal branch (k), passing to the dorsum of the foot, and a plantar branch (j), to the sole of the foot. The dorsal branch is accompanied by the main saphenous nerve (g) and vein. It sends one or two branches to the medial side of the ankle-joint, passes then onto the dorsum of the foot, and divides into four main branches. The medial one passes along the medial side of the medial digit; the other three pass to the intervals between the digits. Each divides into two branches which supply the contiguous sides of the two digits between which the interval lies. The dorsal branch thus supplies arteries to the sides of all the digits except to the lateral side of the lateral digit. This is supplied by A. suralis.

The plantar branch (j) is larger than the dorsal. It passes distad on the medial surface of the flexor longus hallucis, accompanied by the tibial nerve, and across the space between the tendon of Achilles and the flexor. It gives superficial and deep branches to the structures about the ankle-joint, and sends inward a branch from the lateral side (Fig. 128, d) which joins the termination of A. tibialis anterior to form the plantar arch. It then passes distad along the plantar surface of the foot, nearer its medial border. Beneath the pad in the sole of the foot it divides into three branches which supply the interosseous spaces between the three digits.

e. A. poplitea.—The main trunk of the femoral artery passes between the vastus medialis and the semimembranosus and then through the distal portion of the adductor femoris to reach the popliteal space. This is the space ventrad (or caudad) of the knee, between the biceps femoris on one side and the semimembranosus on the other. Here the artery receives the name A. poplitea, or popliteal artery. The popliteal artery gives off a number of large branches as it passes through the popliteal space, passes between the condyles of the femur and underneath the popliteal muscle, and finally turns dorsolaterad between the tibia and fibula, just distad of the head of the fibula. It now receives the name A. tibialis anterior and passes distad along the dorsal (anterior) border of the fibula.

Branches of the popliteal artery:

1. A. suralis.—This is a large branch which passes distad from the caudal side of the popliteal artery. It sends branches to the biceps and to the fat in the popliteal space, and passes onto the ventral border of the lateral head of the gastrocnemius. It sends branches to both heads of the gastrocnemius and to the popliteus, passes distad onto the lateral surface of the tendon of Achilles, and may be traced to the proximal portion of the dorsolateral side of the foot, where it sends many branches to the integument about the ankle-joint. It then passes along the lateral side of the foot and supplies the artery on the lateral side of the fifth digit.

2. Aa. genu posteriores.—Several small arteries which pass to the knee-joint.

3. Rami musculares.—Numerous small branches to the muscles about the popliteal space.

4. A. tibialis posterior.—This is the largest branch of the popliteal artery, which it leaves just before the latter passes beneath the popliteal muscle. The tibialis posterior passes at first mediad, then turns distad, passes across the popliteus muscle onto the surface of the flexor longus hallucis, and ramifies in the substance of this muscle and its tendon. It gives branches also to the gastrocnemius and soleus. (It does not pass into the foot as does the corresponding artery in man.)

5. A. tibialis anterior.—The anterior tibial artery is the continuation of the popliteal after its passage through the interosseous membrane between tibia and fibula to the dorsal side of the lower leg. Here it passes distad, lying against the interosseous membrane, between the extensor longus digitorum and the tibialis anterior muscle, or partly imbedded in the substance of the latter. It passes, lying beneath the tendons of these muscles, through the transverse ligament proximad of the malleoli, thus reaching the dorsum of the foot. It extends distad across the tarsus to the space between the second and third metatarsals, and through this space to the plantar side of the foot (Fig. 128). Here it receives one or two small branches (a and d) from the plantar branch of A. saphena (forming with them the plantar arch (c)), and passing distad and slightly laterad, divides into three main portions (e). These (Aa. digitales plantares) pass to the three intervals between the digits. The medial one passes along the lateral side of the second digit; the next divides, sending a branch to the lateral side of the third digit and the medial side of the fourth; the lateral one passes along the medial border of the fifth digit. The Aa. digitales plantares send numerous branches to the interosseous muscles.

Branches of the tibialis anterior:

a. A. tibialis recurrens.—Immediately after passing through the interosseous membrane the anterior tibial sends a small artery proximad to the knee-joint.

b. Rami musculares.—Numerous short branches throughout the course of the artery, to the muscles about it.

c. Ramus superficialis.—A larger branch leaves the lateral surface of the artery about one-third the distance from the knee to the ankle and passes along with the superficial peroneal nerve, at first beneath M. peroneus longus, then superficially. It passes onto the dorsal surface of the foot and becomes connected with terminal branches of A. saphena.

d. A. tarsea medialis.—This arises from the tibialis anterior just distad of the transverse ligament through which it passes at the ankle, passes over the medial surface of the astragalus, and is distributed to the ligaments about the ankle-joint. It anastomoses with the plantar branch of A. saphena.

e. A. metatarsea.—The metatarsal artery passes laterad from the tibialis anterior at the distal boundary of the tarsus, on the dorsal surface of the foot. It sends branches distad in the intervals between the third and fourth and the fourth and fifth metatarsals.

The distal branches (Fig. 128) of the tibialis anterior have been described in the general description of the artery.

THE VEINS. VENÆ.

Venæ pulmonales. The Pulmonary Veins.

The pulmonary veins follow in the lungs the course of the bronchi. They enter the left auricle in three groups (Fig. 116, page 276). The first of these (i) comes from the anterior and middle lobes of the right side, the second (h) from the corresponding lobes of the left side, and the third (g) from the terminal lobes of both sides. Each group is composed of two or three veins and opens into a sinus or extension of the auricle. The sinuses are from their position dextral (i), sinistral (h), and dorsal (g).

The Veins of the Body.

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.

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.

IV. THE LYMPHATIC SYSTEM. SYSTEMA LYMPHATICUM.

The lymphatic system of the cat has not been worked out in detail, so that only the main features of the system are given in the following account.

The lymphatic system consists of a number of vessels, the lymphatics, containing a colorless fluid called lymph, and of lymphatic glands, connected with the lymphatic vessels. The lymphatic vessels are found throughout the body as slender tubes, frequently united into networks, and containing many valves. They take origin from the spaces in the connective tissue, so that they are at first without definite walls. The fluid in the connective-tissue spaces gradually flows together into tubes with definite walls, and these tubes, the lymphatic vessels, finally join the venous system. In their passage through the lymphatic glands the vessels break up into fine channels which again unite on leaving the gland. In the gland lymph-cells are added to the fluid, and probably other changes are produced.

Most or all of the lymphatic vessels of the body finally unite into two trunks before entering the veins. The largest trunk is the thoracic duct (Fig. 118, 5, page 282), which collects the lymph from the entire caudal half of the body, and from the left forelimb and the left side of the thorax, head, and neck. It passes along the dorsosinistral side of the thoracic aorta, lying against its surface, and enters the left external jugular vein at its junction with the subclavian. The second main trunk is the right lymphatic duct; this collects the lymph from the right side of the thorax, the right forelimb, and the right side of the neck and head; it enters the right external jugular.

1. Lymphatics of the Head.

—A number of lymphatic vessels arise on the sides of the face, especially in the upper and lower lips. They form a superficial network of vessels, lying over the ventral half of the masseter muscle and an area ventrad of it. These lymphatic vessels all enter two large lymphatic glands (Fig. 131, 12, page 322) lying at the ventrocaudal angle of the masseter muscle, covering the union of the anterior and posterior facial veins. Into these glands pass also a number of lymph vessels from the back of the head. From these two lymphatic glands two or three small lymphatic vessels pass caudad, lying on the surface of the external jugular vein. Near the point of the shoulder, some distance craniad of the junction of the external and internal jugular veins, these vessels enter another small lymphatic gland lying on the dorsal surface of the external jugular vein. Thence one or two vessels continue caudad, still on the surface of the external jugular, and finally unite with the deep lymphatics of the head and neck and those of the arm to enter the caudal end of the external jugular vein, usually (on the left side) after junction with the thoracic duct, from the thorax.

The deep lymphatics of the head come from the internal parts of the head,—tongue, pharynx, etc., and enter a large lymphatic gland situated close to the caudoventral surface of the tympanic bulla, at the side of the pharynx. Thence a large lymphatic trunk passes caudad at the side of the trachea, along with the common carotid artery and internal jugular vein, unites with the superficial vessels from the head, above described, joins (on the left side) the thoracic duct, and enters the external jugular vein.

2. Lymphatics of the Neck.

—Two or three lymph-glands are found in the fatty mass in the neck beneath the clavotrapezius and levator scapulæ ventralis muscles. These receive lymphatics from the neck and side of the thorax. The vessels which arise from them join those from the head and arm to enter the external jugular vein.

3. Lymphatics of the Thoracic Limbs.

—The lymphatics of the forelimbs begin as a number of vessels on the dorsum and palm of the hand. These all pass toward the radial side, and at about the base of the first metacarpal the vessels from both sides of the hand unite to form two or three main trunks. These pass towards the elbow, accompanying the vena cephalica (Fig. 130). There are usually two of these main trunks, one lying on each side of the vena cephalica. They accompany this vein over the shoulder, following that portion which finally joins the external jugular. In the hollow of the shoulder they enter the cervical lymph-glands, one or two lymph-glands imbedded in the fat lying beneath the clavotrapezius and levator scapulæ ventralis in this region. From the cervical lymph-glands a single trunk passes mediocaudad, unites with the lymphatics from the head, and usually (on the left side) with the cranial end of the thoracic duct, and enters the external jugular vein at its junction with the subclavian. The common trunk from the head and arm may enter the jugular separately, but close to the termination of the thoracic duct. On the right side the common trunk is joined by one or more small vessels coming from the lymphatic glands of the thorax and forming the right lymphatic duct.

There is said to be also a deep system of lymphatics in the arm, in addition to the superficial system above described; this is said to accompany the branches of the brachial vein. If this system is present in the cat, it is much less easily demonstrated than the superficial system.

4. Lymphatics of the Thorax and Abdomen.

—In the thorax are a number of lymphatic glands which are apparently not constant in number and position. One is commonly found dorsad of the bifurcation of the superior vena cava, one ventrad of the mammary vein, several small ones about the bifurcation of the trachea, one or more in the region of the aortic arch, and a number of small ones scattered in the mediastinum. The vessels from these glands finally join either the right lymphatic duct or the thoracic duct; the details have not been worked out and are probably variable.

In the abdominal cavity a number of mesenteric glands, of considerable size, are found in the mesentery and in the mesocolon. In the mesocolon these are usually separate, forming a chain of glands following the colon about one and a half centimeters from it. In the mesentery the glands are mostly united into a very large one, formerly known as the pancreas aselli; this is the largest lymph-gland in the body. It is a curved structure, four or five centimeters in length, lying in the central region of the mesentery.

Into the mesenteric glands pass lymphatic vessels from the viscera of the abdomen. From the mesenteric glands one or two large lymphatic vessels pass craniodorsad, at first with the portal vein, then dorsad of it. This vessel reaches the dorsal side of the aorta near the cranial end of the kidney, where it enters a large fusiform vessel, the receptaculum chyli, which stretches from the cranial end of the kidney craniad between the crura of the diaphragm into the thorax. The receptaculum receives other lymphatics from the various organs of the abdominal cavity as well as vessels coming from the pelvic region, and from the iliac glands. These lie beside the iliac artery, receive lymphatics from the hind limbs, and send lymphatics craniad to the receptaculum chyli. The latter forms the beginning of the thoracic duct.

The thoracic duct (Fig. 118, 5, page 282) enters the thoracic cavity between the crura of the diaphragm as a continuation of the receptaculum chyli. It lies on the dorsal side of the aorta (a), somewhat to the left. It passes along the aorta, gradually coming to lie more on its left side, and finally leaves that vessel near the aortic arch. The duct continues thence straight craniad along the left side of the œsophagus till it reaches the external jugular vein at its junction with the subclavian. In this region the thoracic duct usually unites with the lymphatics coming from the head and arm, then enters the external jugular vein, or the innominate at the point of union of external jugular and subclavian.

In its passage through the thorax the duct frequently divides into two or three divisions which pass along parallel to each other for a distance, then reunite. Such division into two or three parts is especially frequent just before the union with the jugular vein. The numerous valves in the thoracic duct give it a beaded appearance.

5. Lymphatics of the Pelvic Limbs.

—A number of lymphatic vessels are formed on the dorsum and the sole of the foot. These pass to the lateral side, forming a network on the lateral and dorsal surface of the ankle-joint, and finally unite into two main trunks which accompany the vena saphena parva. In the popliteal space these enter the popliteal gland which lies imbedded in the fat of that region. From the popliteal gland one or two trunks accompany the superficial division of the vena saphena parva across the lateral surface of the biceps muscle, and finally thus reach the pelvic cavity. Here they join the lymphatics of the pelvic region, which all pour their lymph at last into the thoracic duct. Inguinal glands are either very small or not present in the cat.

The pelvic limbs have perhaps a deep system of lymphatics, accompanying the deep veins; if so, they are not easily demonstrable.