Part 66

(3) The =perineal artery= (A. perinei) is relatively small in the male. It passes upward at the side of the anus, which it supplies, and gives twigs to the bulbo-cavernosus muscle and the skin of the perineum. In the female it is large and is distributed to the anus and vulva, and gives a large branch to the vestibular bulb.

(4) The =artery of the bulb= (A. bulbi urethræ) may be regarded as the direct continuation of the internal pudic in the male. It lies at the side of the urethra above the ischial arch, dips under the bulbo-cavernosus muscle, and ramifies in the corpus spongiosum. Before doing so it gives off a small branch which turns around the ischial arch to reach the dorsum penis, and anastomoses with the deep branch of the obturator.

(4_a_) The =artery of the clitoris= (A. clitoridis) is the homologue in the female of the preceding vessel, but is much smaller. It passes to the ventral surface of the vulva with the internal pudic nerve, supplies the clitoris, and gives twigs to the vulva.

3. The =lateral sacral artery= (A. sacralis lateralis) arises at the lumbo-sacral articulation (Fig. 451). It passes backward under the wing of the sacrum, then along the pelvic surface of the bone below the inferior sacral foramina and the nerves emerging from them, and is continued by the lateral coccygeal artery. The branches are as follows:

(1) =Spinal branches= (Rami spinales) enter the vertebral canal through the foramen between the last lumbar vertebra and the sacrum and through the ventral sacral foramina. They give off branches to the spinal cord and its membranes which reinforce the ventral spinal artery, and others which emerge through the dorsal sacral foramina and supply the muscles and skin of the croup.

(2) The =middle coccygeal artery= (A. coccygea) is an unpaired vessel which arises from the right or left lateral sacral or from a lateral coccygeal artery. It passes backward on the pelvic surface of the sacrum to the median line and continues in that position along the tail between the depressor muscles, supplying these and the skin.

(3) The =posterior gluteal= or =ischiatic artery= (A. glutea caudalis) emerges through the upper part of the sacro-sciatic ligament and runs backward and downward on the latter under cover of the biceps femoris (Fig. 455). It gives branches to that muscle and to the semitendinosus and semimembranosus, and anastomoses with the obturator, deep femoral, and posterior femoral arteries.

(4) The =lateral coccygeal artery= (A. caudalis lateralis ventralis) continues the direction of the lateral sacral, but is much smaller than the preceding vessel. It passes back between the depressor and intertransversales muscles of the tail and divides into two branches which supply twigs to the muscles and skin.

4. The =ilio-lumbar artery= (A. iliolumbalis) arises at a right angle from the internal iliac and runs outward behind the sacro-iliac joint, crossing the ventral surface of the ilium under cover of the iliacus muscle. It gives branches to the ilio-psoas and longissimus, and terminates by turning around the external border of the ilium a little behind the external angle, giving branches to the gluteus medius and tensor fasciæ latæ (Fig. 455).

5. The =anterior gluteal artery= (A. glutea cranialis) is the largest branch of the internal iliac. It arises usually opposite to the preceding vessel and passes outward through the great sacro-sciatic foramen, dividing into several branches as it emerges; these enter the gluteal muscles (Fig. 455).

6. The =iliaco-femoral= or =external circumflex artery= (A. cireumflexa femoris lateralis) passes downward and outward across and beneath the shaft of the ilium, under cover of the iliacus muscle, and dips in between the rectus femoris and vastus externus. It is accompanied by two satellite veins. It gives collateral branches to the ilio-psoas, the glutei, and the tensor fasciæ latæ, supplies the nutrient artery of the ilium, and terminates in the quadriceps femoris (Fig. 455).

7. The =obturator artery= (A. obturatoria), the inner terminal branch of the internal iliac, passes downward and backward on the pelvic surface of the shaft of the ilium along the ventral border of the iliac head of the obturator internus, accompanied by the satellite vein and nerve, which lie in front of the artery (Fig. 451). On reaching the anterior border of the obturator foramen it dips under the obturator internus and passes obliquely through the foramen. In this part of its course it gives off a vesical branch and twigs to the obturator internus and the hip joint. After its emergence from the pelvic cavity it runs backward on the ventral face of the ischium, passes through the semimembranosus and, in the male, enters the crus penis, forming the arteria profunda penis. It anastomoses with the internal pudic, and usually with the external pudic by a branch which runs forward on the dorsum penis. Large collateral branches are detached to the adductors of the thigh, the biceps femoris and semitendinosus, forming anastomoses with the deep femoral and posterior femoral arteries. In the female the terminal part is small and enters the root of the clitoris.

ARTERIES OF THE PELVIC LIMB

The main arterial trunk of each pelvic limb descends as far as the lower border of the popliteus muscle, where it divides into the anterior and posterior tibial arteries. The different parts of the trunk receive special names which correspond to the several regions through which it passes. In the abdomen it is termed the =external iliac artery=, in the proximal two-thirds of the thigh it is called the =femoral artery=, while below this it is termed the =popliteal artery=.

THE EXTERNAL ILIAC ARTERY (Figs. 450, 451)

The =external iliac artery= (A. iliaca externa) arises from the aorta under the fifth lumbar vertebra, usually just in front of the origin of the internal iliac. It descends at the side of the pelvic inlet along the tendon of the psoas minor, crosses the insertion of that muscle, and reaches the level of the anterior border of the pubis, where it becomes the femoral artery. It is covered by the peritoneum and fascia, and is related behind to the corresponding vein. Its branches are as follows:

1. The =circumflex iliac artery= (A. circumflexa ilium profunda) arises from the external iliac at its origin or from the aorta directly. It passes across the iliac fascia toward the external angle of the ilium, near which it divides into two branches. The artery lies between the fascia and the peritoneum and is accompanied by two veins and the external cutaneous nerve of the thigh. The =anterior branch= gives twigs to the iliacus and psoas muscles, and passes downward and forward in the flank between the obliquus internus and transversus abdominis, in which it ramifies. The =posterior branch= perforates the abdominal wall and runs downward on the inner face of the tensor fasciæ latæ to the fold of the flank, supplying branches to that muscle, the panniculus, the precrural lymph glands, and the skin.

2. The =cremasteric artery= (A. spermatica externa) is a very small vessel which arises in a variable manner. It springs most often from the external iliac near its origin, but may come from the circumflex iliac, the aorta between the external and internal iliac, or the latter vessel. It accompanies the cremaster muscle to the inguinal canal, supplies twigs to that muscle, the tunica vaginalis, and other constituents of the spermatic cord (Fig. 450).

2_a_. The =middle uterine artery= (A. uterina media) of the female is regarded as the homologue of the preceding vessel. It has a similar origin, but is a much larger artery, which passes between the layers of the broad ligament and reaches the horn of the uterus close to its junction with the body. It is distributed to both, and anastomoses with the anterior and posterior uterine arteries.

THE FEMORAL ARTERY (Figs. 450, 451)

The =femoral artery= is the main arterial trunk of the thigh. It begins at the level of the anterior border of the pubis, from which it is separated by the femoral vein. It descends almost vertically in the femoral canal behind the sartorius muscle, covered at first by the internal femoral fascia and lower down by the gracilis. After passing over the insertion of the pectineus, it perforates the adductor muscle, crosses in the vascular groove of the posterior surface of the femur, and is continued between the two heads of the gastrocnemius as the popliteal artery. It is related at its origin to the sartorius in front, the femoral vein behind (which separates it from the pectineus), and the iliacus externally. Lower down it is related superficially to the deep inguinal lymph glands, and deeply to the vastus internus, while the saphenous nerve is in front of it, and the vein passes to its external face. The chief branches are as follows:

1. The =prepubic artery= (Truncus pudendo-epigastricus) arises from the femoral artery at its origin, usually by a common trunk with the deep femoral. It passes forward and a little inward and downward across the edge of the inguinal ligament, and then runs on the abdominal surface of the ligament to the inner part of the internal inguinal ring, where it divides over the upper border of the internal oblique muscle into the posterior abdominal and external pudic arteries.

(1) The =posterior abdominal artery= (A. epigastrica caudalis) passes along the external border of the rectus abdominis and anastomoses in the umbilical region with the anterior abdominal artery (Figs. 272). It supplies branches to the rectus and obliquus internus muscles.

(2) The =external pudic artery= (A. pudenda externa) descends on the inguinal ligament through the inner part of the inguinal canal and emerges at the inner angle of the external ring. In the male it divides into the =subcutaneous abdominal artery= and the =dorsal artery of the penis=. The former runs forward a short distance from the linea alba, and gives branches to the superficial inguinal lymph glands, the sheath, and the scrotum. The latter passes to the dorsum penis and ends at the glans as the arteria glandis. It gives off collateral branches (Rami profundi penis) to the corpus cavernosum, one of which usually passes backward and anastomoses with a branch of the obturator artery. Branches are also supplied to the superficial inguinal lymph glands, the prepuce, and the scrotum. In the female the =mammary artery= takes the place of the dorsal artery of the penis; it plunges into the base of the mammary gland.

2. The =deep femoral artery= (A. profunda femoris) arises either by a common trunk with the prepubic or a little distal to it (Fig. 451). It passes backward and downward across the inner face of the femoral vein, then below the pubis in the space between the hip joint and the pectineus muscle. On reaching the obturator externus it inclines more ventrally and outward, passes out between the internal border of the femur and the quadratus femoris, and ramifies in the biceps femoris and semitendinosus. It supplies large collateral branches to the adductor muscles and twigs to the deep inguinal lymph glands and the hip joint.

3. The =anterior femoral artery= (A. femoralis cranialis) arises a little distal to the preceding vessel from the opposite side of the femoral trunk. It passes forward, outward, and a little downward across the deep face of the sartorius, and dips in between the rectus femoris and vastus internus (Fig. 451). It is related externally to the ilio-psoas and the femoral nerve.

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.

ANTERIOR TIBIAL ARTERY

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.