Part 62

3. The =anterior branch= divides after a very short course into the dorsal and middle colic arteries.

(1) The =dorsal=, =left=, or =retrograde colic artery= (A. colica dorsalis) is a large vessel which passes along the dorsal (fourth and third) parts of the great colon to the pelvic flexure, where it joins the ventral colic artery.

(2) The =middle colic artery= or =first artery of the small colon= (A. colica media) is a much smaller vessel which passes to the origin of the small colon, enters the colic mesentery, and forms an arch by joining the first branch of the posterior mesenteric artery close to the lesser curvature of the bowel. It sends an anastomotic branch to the dorsal colic artery.

III. The =renal arteries= (Aa. renales), right and left, are relatively large vessels which arise from the aorta near the anterior mesenteric. The =right artery= is the longer of the two. It crosses over the dorsal surface of the vena cava to the right and somewhat forward. At the hilus it divides into several (five to eight) branches; some of these enter the gland at the hilus, while others pass to the ventral surface and enter there. The =left artery= is short and usually arises a little further back; it passes directly outward to the kidney and is then disposed like the right one. Small collateral branches are supplied to the ureters and the adrenals. The latter also receive small vessels directly from the aorta. The distribution within the kidney has been described.

Variations in the renal arteries are frequent. Two or more arteries may occur on one or both sides. Accessory arteries are more common on the left side and usually enter the posterior pole of the gland. They may arise from the aorta, the external iliac, or the circumflex iliac artery.

IV. The =posterior= or =small mesenteric artery= (A. mesenterica caudalis) is an unpaired vessel which arises from the ventral face of the aorta at the fourth lumbar vertebra, _i. e._, about five or six inches (ca. 12 to 15 cm.) behind the origin of the anterior mesenteric artery. It is much smaller than the latter and supplies the greater part of the small colon and rectum. It descends in the colic mesentery and divides into two branches. The anterior branch (A. colica sinistra) gives off three or four arteries which divide and form anastomotic arches close to the bowel. The first arch is formed by union with the middle colic branch of the anterior mesenteric. The posterior branch or anterior hæmorrhoidal artery (A. hæmorrhoidalis cranialis) passes backward in the upper part of the mesentery and the mesorectum and terminates near the anus by anastomosing with the internal pudic artery. Three or four of its anterior collateral branches form arches.

V. The =spermatic arteries= (Aa. spermaticæ internæ), right and left, are long slender arteries which arise from the aorta near the posterior mesenteric and supply the testicle and epididymis. Each passes backward in a narrow fold of peritoneum (Plica vasculosa) to the internal inguinal ring and descends through the inguinal canal to the scrotum. In the canal and scrotum it pursues a very flexuous course in the anterior border of the spermatic cord, surrounded by the pampiniform plexus of veins, and associated closely with the spermatic nerves and lymphatics and unstriped muscle-fibers. It passes between the epididymis and testicle, runs in flexuous fashion along the attached border of the latter, turns around the posterior pole, and runs forward on the free border to the anterior pole. The largest branches arise from its ventral part, pass tortuously up either side of the gland embedded in the tunica albuginea, and give off fine branches to the gland substance. Small collateral branches are detached to the ureter and the spermatic cord.

The =utero-ovarian arteries= in the female correspond to the preceding vessels, but are much shorter. Each is placed in the anterior part of the broad ligament of the uterus and divides into ovarian and uterine branches. The =ovarian branch= (A. ovarica) pursues a flexuous course to the ovary, which it supplies. The =uterine branch= (A. uterina cranialis) passes to the concave border of the cornu of the uterus, which it supplies, anastomosing with the uterine artery.

VI. The =lumbar arteries= (Aa. lumbales) are in series with the intercostal arteries and have a similar origin and distribution. There are usually six pairs of lumbar arteries, of which five arise from the aorta and the sixth from the internal iliac or the lateral sacral at the junction of the last lumbar vertebra and the sacrum. Each passes across the body of a lumbar vertebra to the intertransverse space, gives branches to the sublumbar muscles, and divides into dorsal and ventral branches. The =dorsal branch= (Ramus dorsalis), the larger of the two, passes upward to ramify in the extensor muscles of the spine and the skin of the loins; it gives off a =spinal branch= (Ramus spinalis) which comports itself like the corresponding branch of an aortic intercostal artery. The =ventral branch= (Ramus ventralis) runs outward in the intertransverse space, passes between the transversus and obliquus internus abdominis, gives branches to these muscles, and ends in the obliquus externus, the panniculus, and the skin of the flank.

[Illustration:

FIG. 451.—DISSECTION OF PELVIS, THIGH, AND UPPER PART OF LEG OF HORSE, INTERNAL VIEW.

_L_, Lumbar vessels; _V.c._, posterior vena cava; _A_, aorta (termination); _C_, sympathetic trunk; _1_, internal iliac artery, _2_, lateral sacral artery; _3_, middle coccygeal artery; _4_, lateral coccygeal artery; _5_, umbilical artery (cut off); _6_, internal pudic artery; _6′_, vesico-prostatic artery; _7_, obturator artery; _8_, a. profunda penis (from left obturator); _9_, posterior gluteal (or ischiatic) vessels; _10_, external iliac artery; _11_, _11′_, deep femoral artery; _12_, prepubic artery; _13_, branch of deep femoral artery; _14_, great sciatic nerve; _15_, posterior gluteal nerve; _16_ (above), internal pudic nerve; _16_ (below near pelvic outlet), suburethral venous plexus; _17_, sacro-coccygeus inferior; _18_, coccygeus; _19_, recto-coccygeus; _20_, retractor ani; _21_, _21′_, two heads of obturator internus; _22_, symphysis pelvis; _23_, prepubic tendon; _24_, suspensory ligament of penis; _25_, retractor penis muscle; _26_, bulbo-cavernosus muscle; _27_, urethra (cross-section); _28_, crus penis (cross-section); _29_, suspensory ligaments of anus (= upper part of retractor penis muscle); _30_, anal lymph glands; _31_, tibial nerve. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

THE INTERNAL ILIAC ARTERY

The =internal iliac= or =hypogastric arteries= (Aa. hypogastricæ) result from the bifurcation of the aorta under the fifth or sixth lumbar vertebra. They diverge at an angle of about 60 degrees, and each passes backward under the wing of the sacrum, then inclines downward on the pelvic surface of the shaft of the ilium, and divides a little above the psoas tubercle into iliaco-femoral and obturator arteries. The chief branches are as follows:

[Illustration:

FIG. 452.—DISSECTION OF PERINEUM OF HORSE (MALE).

_1_, Bulbo-urethral (Cowper’s) gland; _2_, transversus perinei muscle (?); _3_, ischio-urethral muscle; _4_, retractor penis muscle; _5_, bulbo-cavernosus muscle. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

1. The last pair of =lumbar arteries= pass up through the foramina at the junction of the last lumbar vertebra and the sacrum.

2. The =internal pudic artery= (A. pudenda interna) arises near the origin of the internal iliac. It passes backward and somewhat downward, at first along the iliac head of the obturator internus, then above the superior ischiatic spine on the inner surface of the sacro-sciatic ligament, perforates the latter and runs for a variable distance in its substance or on its external face. It then re-enters the pelvic cavity, passes backward on the retractor ani to the ischial arch, and divides into the perineal and the artery of the bulb in the male, perineal and artery of the clitoris in the female. It is accompanied by the internal pudic nerve. Its chief branches are as follows:

(1) The =umbilical artery= is given off from the internal pudic about an inch (ca. 2 to 3 cm.) from the origin of that vessel. It is a very large artery in the fœtus, in which it curves downward and forward at the side of the bladder in the edge of the umbilical fold of peritoneum, passes through the umbilical opening, becomes a component of the umbilical cord and ramifies in the fœtal placenta. After birth it extends only to the vertex of the bladder and is much reduced. Its lumen is almost obliterated and its wall is very thick, giving the vessel a cord-like character, hence it is commonly termed the round ligament of the bladder.[167] It gives off small =vesical branches= (Aa. vesicates craniales) to the bladder, and twigs to the prostate and vasa deferens in the male. In the mare a small branch runs forward along the ureter into the broad ligament of the uterus.

[Illustration:

FIG. 453.—DISSECTION OF PERINEUM OF MARE.

_1_, Sacro-coccygeus superior; _2_, sacro-coccygeus lateralis; _3_, intertransversales; _4_, sacro-coccygeus inferior; _5_, recto-coceygeus; _6_, sphincter ani externus; _6′_, branch connecting sphincter ani with constrictor vulvæ; _7_, vestibular bulb; _8_, tuber ischii; _9_, sacro-sciatic ligament. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

(2) The =middle hæmorrhoidal= or =vesico-prostatic artery= (A. hæmorrhoidalis media) in the male arises usually near the prostate and runs backward lateral to the rectum. It supplies branches to the rectum, bladder, urethra, and accessory genital glands. In the female the homologous vessel is much larger and gives off the =posterior uterine artery= (A. uterina caudalis). This runs forward on the side of the vagina, to which it gives branches, and ramifies on the body of the uterus, anastomosing with the anterior and middle uterine arteries. (In some cases this artery arises from the internal iliac or the umbilical.)

(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.

[Illustration:

FIG. 454.-CROSS-SECTION OF TAIL OF HORSE.

_1_, Dorso-lateral coccygeal vessels and nerve; _2_, ventro-lateral coccygeal artery and nerve; _3_, middle coccygeal artery; _4_, sacro-coccygeus superior; _4′_, sacro-coccygeus lateralis; _5_, _5′_, intertransversales; _6_, sacro-coccygeus inferior; _7_, recto-coccygeus; _8_, coccygeal fascia; _9_, fibro-cartilage between fourth and fifth coccygeal vertebra. The veins are black. ]

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.

[Illustration:

FIG. 455.—DISSECTION OF PELVIS, THIGH, AND LEG OF HORSE, EXTERNAL VIEW.

_1_, Dorsal branches of last intercostal and first three lumbar nerves; _2_, cutaneous branch of fourth lumbar nerve; _3_, ventral branches of last intercostal nerve: _4_, branches of ilio-hypogastric nerve; _5_, superficial branch of ilio-inguinal nerve; _6_, great sciatic nerve; _7_, _8_, nerves to biceps femoris (from posterior gluteal nerve); _9_, nerve to semitendinosus (from same); _10_, posterior cutaneous nerve of thigh; _11_, internal pudic nerve; _12_, anterior gluteal vessels and nerves; _13_, posterior gluteal (or ischiatic) vessels; _14_, branches of obturator vessels; _15_, proximal muscular branches of great sciatic nerve to biceps femoris, semitendinosus, and semimembranosus; _16_, nerve to tensor fasciæ latæ (from anterior gluteal nerve); _17_, gluteus profundus; _18_, stump of gluteus medius; _19_, gemellus; _20_, trochanter major; _21_, stump of biceps femoris; _22_, sacro-coccygeus superior; _22′_, sacro-coccygeus lateralis; _23_, coccygeus; _24_, sacro-coccygeus inferior; _25_, line of fusion of aponeuroses of internal and external oblique muscles of abdomen; _25′_, aponeurosis of external oblique muscle (lamina iliaca); _26_, branches of iliaco-femoral vessels; _27_, ilio-lumbar vessels; _28_, ilio-lumbar ligament or deep layer of lumbo-dorsal fascia; _29_, external angle of ilium; _30_, internal angle of ilium; _31_, lateral sacro-iliac ligament; _32_, sacro-sciatic ligament. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

(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).

[Illustration:

FIG. 456.—DEEP DISSECTION OF VENTRAL WALL OF PELVIS OF HORSE (MALE).

_1_, External pudic artery and small satellite vein; _2_, anastomosis between external pudic and internal circumflex veins; _3_, accessory ligament; _4_, round ligament; _5_, transverse ligament; _6_, head of femur; _7_, obturator externus (stumps); _8_, inner margin of obturator foramen; _9_, origin of gracilis; _10_, origin of adductor; _11_, bulbo-cavernosus; _12_, retractor penis; _13_, suspensory ligament of penis. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

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:

[Illustration:

FIG. 457.—DISSECTION OF INGUINAL REGION AND INNER SURFACE OF THIGH OF HORSE.

_1_, External pudic artery; _2_, anterior branches of _1_; _3_, posterior branches of _1_; _4_, transverse anastomosis between external pudic veins; _4′_, venous plexus of dorsum penis; _5_, femoral artery; _6_, saphenous nerve; _7_, anterior border of external inguinal ring; _8_, obliquus abdominis internus; _9_, posterior border of external inguinal ring; _10_, tunica vaginalis; _11_, vas deferens; _12_, cremaster muscle; _13_, prepuce; _14_, glans penis; _15_, external urethral orifice; _16_, posterior branches of circumflex iliac vessels; _17_, saphenous vessels; _18_, fold of flank; _19_, penis (cut); _A_, superficial inguinal lymph glands; _B_, precrural lymph glands; _C_, deep inguinal lymph glands. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ]

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.