Part 63

In some cases this artery is replaced by a large branch of the external circumflex, which passes between the ilio-psoas and rectus femoris and enters the interstice between the latter muscle and the vastus internus.

4. Innominate =muscular branches= (Rami musculares) of variable size and arrangement are given off to the muscles of this vicinity.

5. The =saphenous artery= (A. saphena) is a small vessel which arises from the femoral about its middle or from a muscular branch, and emerges between the sartorius and gracilis or through the latter to the inner surface of the thigh (Fig. 457). It is joined by the large saphenous vein and the saphenous nerve and passes down superficially on the fore part of the gracilis, continues on the deep fascia of the leg, and divides above the hock into two branches, which accompany the radicles of the vein. It gives off cutaneous twigs and anastomoses with the recurrent tibial artery.

In some cases this anastomosis does not occur. The artery may be larger and directly continuous with the internal tarsal artery.

6. The =articular branch= (A. genu suprema) is a slender artery which arises from the femoral just before it passes through the adductor. It descends along the posterior border of the vastus internus to the inner surface of the stifle joint, where it ramifies.

7. The =nutrient artery of the femur= (A. nutritia femoris) is given off at the middle of the femur and enters the nutrient foramen.

8. The =posterior femoral= or =femoro-popliteal artery= (A. femoris caudalis) is a large vessel which arises from the posterior face of the femoral just before the trunk passes between the two heads of the gastrocnemius (Fig. 455). It is very short and divides into two branches. The ascending branch passes upward and outward between the adductor (in front) and the semimembranosus (behind), and enters the biceps femoris, in which it ramifies. The descending branch passes downward and backward on the external head of the gastrocnemius, then curves upward between the biceps femoris and semitendinosus (crossed externally by the tibial nerve) and divides into branches to these muscles. A branch is detached from the convexity of the curve which passes down between the heads of the gastrocnemius, gives branches to that muscle and the flexor perforans, and is continued by a slender artery which accompanies the tibial nerve and unites with the recurrent tibial artery. A branch ascends alongside of the sciatic nerve between the biceps and semitendinosus and anastomoses with a descending branch of the obturator.

THE POPLITEAL ARTERY

This artery (A. poplitea) is the direct continuation of the femoral. It lies between the two heads of the gastrocnemius, at first on the posterior face of the femur, then on the femoro-tibial joint capsule. It then passes down through the popliteal notch under cover of the popliteus, inclines outward, and divides near the upper part of the interosseous space into anterior and posterior tibial arteries. The satellite vein lies along its inner side. Collateral branches are supplied to the stifle joint and the gastrocnemius and popliteus.

POSTERIOR TIBIAL ARTERY

The =posterior tibial artery= (A. tibialis posterior) is much the smaller of the two terminals of the popliteal. It lies at first between the tibia and the popliteus, then between that muscle and the deep and inner heads of the deep flexor. Lower down it descends along the tendon of the inner head, becomes superficial in the distal third of the leg, and passes behind the tendon. At the level of the tuber calcis it forms an ᔕ-shaped curve, runs downward along the deep flexor tendon accompanied by the plantar nerves, and divides at the lower part of the hock into internal and external plantar arteries. The collateral branches are as follows:

1. The =nutrient artery of the tibia= (A. nutritia tibiæ).

2. =Muscular branches= (Rami musculares) to the popliteus and deep flexor.

3. The =external tarsal artery= (A. tarsea lateralis) arises at the distal end of the leg and is distributed to the outer surface of the hock. It gives off a small recurrent branch which ascends along the external border of the gastrocnemius tendon and anastomoses with a branch of the posterior femoral artery.

4. The =recurrent tibial artery= (A. tibialis recurrens) is given off from the second part of the curve, ascends in relation to the tibial nerve, and anastomoses with the descending branch of the posterior femoral and with the saphenous artery.

5. Small branches (internal calcaneal) to the inner aspect of the hock.

6. The =plantar arteries=, internal and external (A. plantaris medialis, lateralis), are the small terminals of the posterior tibial. They descend along the sides of the tarsal sheath of the deep flexor with the plantar nerves to the proximal part of the metatarsus, where they unite with the perforating tarsal artery to form the =plantar arch= (Arcus plantaris). Four =plantar metatarsal arteries= proceed from this arch. The two slender =superficial plantar metatarsal arteries= (A. metatarsea plantaris superficialis medialis, lateralis) descend on either side of the deep flexor tendon with the plantar nerves and unite with the great metatarsal or with the corresponding digital artery. The two =deep= or =interosseous plantar metatarsal arteries= (A. metatarsea plantaris profundus medialis, lateralis) descend between the suspensory ligament and the corresponding small metatarsal bone and unite near the fetlock with the great metatarsal. The inner artery is the larger of the two and usually appears to be the continuation of the perforating tarsal. It supplies the nutrient artery of the large metatarsal bone. In other cases it is the direct continuation of the internal plantar artery, the external artery only uniting with the perforating tarsal.

[Illustration:

FIG. 458.—DISSECTION OF LEG AND HOCK OF HORSE, INNER VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

ANTERIOR TIBIAL ARTERY

[Illustration:

FIG. 459.—DEEP DISSECTION OF RIGHT STIFLE, LEG, AND HOCK OF HORSE, POSTERIOR VIEW.

The hock is flexed at a right angle, and the tuber calcis is sawn off. The tibial nerve is drawn inward to show its muscular branches. Branches of tibial nerve: _1_, _2_, to gastrocnemius; _3_, _4_, to superficial flexor; _5_, to popliteus; _6_, to flexor longus or accessorius; _7_, to deep flexor. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

[Illustration:

FIG. 460.—SUPERFICIAL DISSECTION OF RIGHT STIFLE, LEG, AND HOCK OF HORSE, FRONT VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

The =anterior tibial artery= (A. tibialis anterior) is much the larger of the two terminal branches of the popliteal. It passes forward through the upper part of the interosseous space and descends with two satellite veins on the outer part, of the front of the tibia, under cover of the tibialis anterior. At the lower part of the leg it deviates to the outer border of the tendon of this muscle, passes on to the capsule of the hock joint, gives off the perforating tarsal artery, and is continued asthe great metatarsal artery. It gives off =muscular branches= to the dorso-lateral group of muscles of the leg and =articular branches= to the hock. The =peroneal= branch (A. peronea) is a variable vessel which descends along the fibula under the lateral extensor; it gives off muscular branches and one which perforates the fascia and divides into ascending and descending cutaneous twigs.

The =perforating tarsal artery= (A. tarsea perforans) is given off under cover of the outer tendon of the peroneus tertius. It passes backward through the vascular canal of the tarsus with a satellite vein and unites on the upper part of the suspensory ligament with the plantar arteries (or only with the external plantar) to form the plantar arch.

In well-injected specimens it is seen that there is a fine arterial network (Rete tarsi dorsale) on the flexor surface of the hock, which is formed by twigs from the anterior tibial and lateral tarsal arteries. From it proceed two very slender =dorsal metatarsal arteries=. The inner one descends in the furrow between the inner small and large metatarsal bones, and anastomoses usually in the proximal part of the metatarsus with the internal superficial plantar metatarsal, uniting sometimes with the deep plantar metatarsal. The external vessel passes down under the periosteum on the anterior face of the large metatarsal bone and becomes lost or joins the large metatarsal artery.

Sometimes the anterior tibial artery passes undivided through the tarsus, gives off the internal deep plantar metatarsal, and is continued as a very large internal superficial plantar metatarsal along the deep flexor tendon, thus resembling the arrangement in the fore limb.

In a few cases the perforating tarsal is a large vessel, directly continuing the anterior tibial, and is continued by a large internal deep plantar metatarsal. The great metatarsal is then small. Other variations are common.

THE GREAT METATARSAL ARTERY

This artery (A. metatarsea dorsalis lateralis) is the direct continuation of the anterior tibial. It passes downward and outward under the extensor brevis and the tendon of the lateral extensor, at first on the joint capsule and then in the oblique vascular groove on the upper part of the large metatarsal bone. It then descends in the groove formed by the apposition of the large and external small metatarsals, inclines inward between the two, and divides on the lower part of the posterior face of the large metatarsal bone into the internal and external digital arteries. It is not usually accompanied by a vein. Beyond this the arterial arrangement is the same as in the thoracic limb.

THE VEINS[168]

PULMONARY VEINS

The terminal =pulmonary veins= (Vv. pulmonales), usually seven or eight in number, return the aërated blood from the lungs and open into the left atrium of the heart. They are destitute of valves. Their tributaries arise in the capillary plexuses in the lobules of the lungs, and unite to form larger and larger trunks which accompany the branches of the bronchi and pulmonary arteries. A very large vein is formed by the union at an acute angle of a trunk from each lung, where the latter are adherent to each other.

SYSTEMIC VEINS

THE VEINS OF THE HEART (Figs. 426, 427)

The =coronary sinus= (Sinus coronarius) is a very short bulbous trunk which receives most of the blood from the wall of the heart. It is situated just below the termination of the posterior vena cava and is covered in part by a thin layer of ventricular muscle-fibers. It opens into the right atrium just below the posterior vena cava. It is formed by the union of two tributaries. The =great cardiac= or =left coronary vein= (V. cordis magna) begins at the left side of the apex of the heart, ascends in the left longitudinal groove and turns backward in the coronary groove, in which it winds around the posterior border of the heart to the right side and joins the coronary sinus. The =middle cardiac= or =right coronary vein= (V. cordis media) begins on the right side of the apex, ascends in the right longitudinal groove and joins the coronary sinus, or opens separately into the atrium just in front of the orifice of the left vein, so that a common trunk (coronary sinus) does not then exist.

The =small cardiac veins= (Vv. cordis minores), three to five in number, are small vessels which return some blood from the right ventricle and atrium; they open into the latter near the coronary groove in spaces between the musculi pectinati.

THE ANTERIOR VENA CAVA (Fig. 429)

The =anterior vena cava= (V. cava cranialis) returns to the heart the blood from the head, neck, thoracic limbs, and the greater part of the thoracic wall. It is formed at the ventral part of the thoracic inlet by the confluence of the two jugular and two brachial veins. Its origin is attached to the first pair of ribs. It passes backward in the anterior mediastinum, at first median and ventral to the common carotid trunk, then deviates to the right of the anterior aorta, and opens into the right atrium opposite to the third rib. The demarcation between vein and atrium is not very distinct. It contains no valves except at the mouths of its radicles. Its length is about five to six inches (ca. 12 to 15 cm.) and its caliber about two inches (ca. 5 cm.) in a subject of medium size. Its right face is crossed by the right phrenic nerve, and on the left it is related to the anterior aorta and brachiocephalic artery. It receives, in addition to small pericardial and mediastinal veins, the following tributaries:

1. The =internal thoracic vein= (V. thoracica interna) is a satellite of the artery of that name. It opens into the anterior vena cava at the first rib.

2. The =vertebral vein= (V. vertebralis) corresponds to the homonymous artery. On the right side it terminates either in front of the deep cervical vein or by a short common trunk with it. On the left side it almost always unites with the deep cervical and vertebral vein to form a common trunk.

3. The =deep= or =superior cervical vein= (V. cervicalis profunda) corresponds to the artery. On the right side it leaves the artery at the first intercostal space, crosses the right face of the trachea and opens into the vena cava; it may form a common trunk with the dorsal or vertebral. On the left side there is nearly always a common trunk for all three.

4. The =dorsal vein= (V. costo-cervicalis) corresponds to the artery. On the right side it leaves the artery on entering the thorax, crosses the right face of the trachea, and opens into the vena cava in front of the deep cervical or by a common trunk with it. On the left side it almost always joins the deep cervical and vertebral to form a short common trunk which crosses the left face of the intrathoracic part of the brachial artery opposite the second rib and opens into the anterior vena cava.

THE VENA AZYGOS

The =vena azygos= (Fig. 429) is an unpaired vessel which arises at the level of the first lumbar vertebra by radicles coming from the psoas and the crura of the diaphragm; it is connected with the first lumbar vein. It passes forward along the right side of the bodies of the thoracic vertebræ, in contact usually with the thoracic duct, which separates the vein from the aorta. At the seventh vertebra it leaves the spine, curves downward and forward over the right side of the thoracic duct, trachea, and œsophagus, and opens into the right atrium opposite the third intercostal space. Its tributaries are:

1. The last fourteen =intercostal veins= (Vv. intercostales) of the right side. On the left side the last four to seven intercostal veins usually empty into the =vena hemiazygos=. This vessel runs on the left side of the aorta from the fourteenth to the eleventh thoracic vertebra, passes between the aorta and the spine, and joins the vena azygos. In its absence its tributaries join the vena azygos.

2. The =œsophageal vein= (V. œsophagea), satellite of the œsophageal artery, joins the vena azygos as it inclines downward.

3. The =bronchial vein= (Vena bronchialis) unites with the preceding to form a short common trunk (Ellenberger-Baum), or empties into the great coronary vein (Chauveau).[169]

VEINS OF THE HEAD AND NECK

JUGULAR VEINS

The =jugular veins= (Vv. jugulares), right and left (Fig. 431), arise behind the posterior border of the lower jaw about two and a half inches (ca. 6 to 7 cm.) below the temporo-maxillary articulation by the union of the superficial temporal and internal maxillary veins. Each passes downward and backward, at first embedded more or less in the parotid gland, and continues in the jugular furrow to the thoracic inlet, where it unites with its fellow and the two brachial veins to form the anterior vena cava. In the neck it is covered by the skin, fascia, and panniculus, and is superficial to the carotid artery, from which it is separated in the anterior two-thirds of the region by the omo-hyoideus muscle.[170] It contains valves at the mouths of its tributaries and has several pairs of semilunar valves variably disposed along its course. Its tributaries are as follows:

1. The =internal maxillary vein= (V. maxillaris interna) is larger than the external maxillary. It may be considered to begin as the continuation backward of the buccinator vein where the vessel crosses the alveolar border of the mandible (about two inches (ca. 5 cm.) behind the last molar tooth). It runs backward on the inner surface of the ramus below the external pterygoid and covered by the internal pterygoid muscle for a distance of about three inches (ca. 7 to 8 cm.), then inclines a little downward and runs ventral to the artery for about an inch (ca. 2 to 3 cm.). It crosses the external face of the artery at the posterior border of the jaw, and is joined by the superficial temporal vein to form the jugular. Its principal radicles are:

(1) The =dorsal lingual vein= (V. dorsalis linguæ), which is a satellite of the lingual nerve.

(2) The =inferior alveolar= or =dental vein= (V. alveolaris mandibulæ), a satellite of the corresponding artery. It often unites with the preceding.

(3) =Pterygoid veins= (Rami pterygoidei).

(4) The =deep temporal vein= (V. temporalis profunda) is a large vessel which receives tributaries from the temporalis muscle and emissaries from the parieto-temporal canal. It is connected with the anterior cerebral vein and usually with the meningeal veins by its frontal branch. The latter drains chiefly the lacrimal gland and passes behind the supraorbital process.

2. The =superficial temporal vein= (V. temporalis superficialis) is a satellite of the corresponding artery. It is formed by the confluence of the =anterior auricular= and =transverse facial veins=. The former receives the =superior cerebral vein= (V. cerebralis dorsalis), which is the emissary of the transverse sinus of the dura mater; it emerges from the parieto-temporal canal behind the postglenoid process. The =transverse facial vein= (V. transversa faciei) runs at first above the artery of like name, then plunges deeply into the masseter and unites in front with the facial vein. It is connected with the vena reflexa.

3. The =inferior masseteric= or =maxillo-muscular vein= (V. masseterica) joins the jugular at the upper border of the sterno-cephalicus tendon. It is a short trunk formed by the confluence at the posterior border of the jaw of masseteric and pterygoid veins. The former is usually connected by a large branch with the buccinator vein.

[Illustration:

FIG. 461.—SUPERFICIAL VESSELS AND NERVES OF HEAD AND ANTERIOR PART OF NECK OF HORSE.

_a_, Masseter; _b_, parotid gland; _c_, parotido-auricularis; _1_, masseteric artery; _2_, parotid branch; _3_, transverse facial artery; _4_, facial artery; _5_, _6_, inferior labial artery; _7_, superior labial artery; _8_, lateral nasal artery; _9_, infraorbital artery; _10_, dorsal nasal artery; _11_, angular artery of eye; _12_, _13_, jugular vein; _14_, great auricular vein; _15_, masseteric vein; _16_, superficial temporal vein; _17_, transverse facial vein; _17′_, deep temporal vein; _18_, external maxillary vein; _19_, facial vein; _20_, labial vein; _21_, dorsal nasal vein; _22_, lateral nasal vein; _23_, angular vein of eye; _24_, _25_, facial nerve; _25′_, _25″_, superior and inferior buccal nerves; _26_, transverse facial nerve; _27_, auriculo-palpebral nerve; _28_, anterior auricular nerve; _29_, cervical branch of facial nerve; _30_, ventral branch of second cervical nerve; _30′_, _30″_, _30‴_, auricular and cutaneous branches of _30_; _31_, branches of dorsal division of first and second cervical nerves; _32_, dorsal branch of spinal accessory nerve. (After Leisering’s Atlas.) ]

4. The =great auricular vein= (V. auricularis magna) is a satellite of the posterior auricular artery above, but joins the jugular a variable distance below and behind the point of origin of the artery.

5. The =inferior cerebral vein= (V. cerebralis ventralis) is an emissary of the cavernous sinus of the dura. It is a satellite of the internal carotid artery, receives the =condyloid vein=, and joins the jugular near the occipital vein or by a common trunk with it.

6. The =occipital vein= (V. occipitalis) arises in the fossa atlantis by the union of muscular and cerebrospinal branches. The former comes from the muscles of the poll and passes through the foramen transversarium. The latter is connected with the occipital sinus of the dura mater and emerges from the spinal canal by the intervertebral foramen.

7. The =external maxillary= or =facial vein= (V. maxillaris externa) arises by radicles which correspond in general to the branches of the artery of like name. It passes down over the cheek along the anterior border of the masseter muscle behind the artery, crossing over the parotid duct, which lies behind the vein lower down. Thus on the ramus and as they turn around its lower border the artery is in front, the vein in the middle, and the duct posterior. In the submaxillary space the vein is ventral to the artery for some distance, then parts company with the artery, runs straight backward along the lower border of the parotid gland, and opens into the jugular vein at the posterior angle of the gland.[171] The chief differences in the tributaries of the vein as compared with the branches of the corresponding artery are as follows:

The =labial veins= (Vv. labiales) form a plexus in the submucous tissue of the cheek from which two veins emerge. The upper one passes back and joins the buccinator vein. The lower one (V. labialis communis) joins the external maxillary vein.

Three veins connect with the external maxillary at the anterior border of the masseter.

The upper one is the =transverse facial=, which unites close to the end of the facial crest.

A little lower is the large valveless =vena reflexa= or =alveolar vein=. This passes back under the upper part of the masseter on the maxilla, turns around the tuber maxillare, perforates the periorbita, and joins the ophthalmic vein. It is relatively small at each end, but presents one or two large fusiform dilatations. It receives the following tributaries: (_a_) The =palatine vein= (V. palatina major), which separates from the palatine artery at the anterior palatine foramen and passes in the groove between the tuber maxillare and the palate bone. The palatine veins form a very rich plexus of valveless vessels in the submucosa of the hard palate, which consists of several layers anteriorly. (_b_) The =sphenopalatine vein= (V. sphenopalatina) forms a rich plexus of valveless vessels on the turbinal bones and the septum nasi. It is usually joined by the =infraorbital vein= (V. infraorbitalis) to form a short common trunk.

[Illustration:

FIG. 462.—DISSECTION OF SUBMAXILLARY SPACE AND ADJACENT PART OF NECK OF HORSE.

_a_, Ramus of mandible; _b_, sterno-cephalicus muscle; _c_, _c′_, omo-hyoidei and sterno-hyoidei (portion removed on right side); _d_, hyoid bone; _e_, anterior belly of digastricus; _f_, _g_, mylo-hyoideus; _h_, submaxillary lymph glands (portion removed on right side); _i_, parotid gland; _k_, submaxillary gland; _l_, chin; _m_, stylo-maxillaris; _1_, parotid duct; _2_, facial vein; _3_, facial artery; _4_, external maxillary vein; _5_, sublingual vein; _6_, sublingual artery; _7_, ventral branch of first cervical nerve; _8_, mylo-hyoid nerve. (After Ellenberger, in Leisering’s Atlas.) ]

The venous plexuses are remarkably developed in certain parts of the nasal mucosa. On the septum a little below its middle and on the turbinals the veins are in several layers. The olfactory region does not share in this arrangement and the veins here are small and join the ethmoidal vein.

(_c_) The =ophthalmic vein= (V. ophthalmica) is a short trunk, connected in front with the vena reflexa and behind with the cavernous sinus through the foramen lacerum orbitale. It receives veins which correspond to the arterial branches.