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circumflex iliac arteries; it also gives off a spinal branch, which enters the intervertebral foramen between the fifth lumbar vertebra and the sacrum, and is distributed like the spinal branches of the lumbar and the aortic intercostal arteries.
2. Arteriæ Sacrales Laterales.-There is sometimes only a single lateral sacral artery on each side; more commonly there are two, superior and inferior.
Both run downwards and medially, on the front of the sacrum. The inferior passes anterior to the piriformis and the sacral nerves, and descends, on the lateral side of the sympathetic trunk, to the coccyx, where it terminates by anastomosing with the middle sacral. The superior branch reaches only as far as the first or the second anterior sacral foramen; then it enters the sacral canal. It anastomoses with the lower branch and with the middle sacral artery. Branches are given off by the lateral sacral arteries to the piriformis, and to the sacral nerves. Spinal offsets are also given off, which pass through the anterior sacral foramina to the sacral canal; they supply the membranes of the spinal medulla, the roots of the sacral nerves, and the filum terminale, and anastomose with other spinal arteries. They then pass through the posterior sacral foramina, and anastomose on the back of the sacrum with branches of the superior and inferior gluteal arteries.
3. Arteria Glutaa Superior (Figs. 774 and 776).-After giving off the iliolumbar and lateral sacral branches, the posterior division of the hypogastric artery is continued as the superior gluteal artery. This is a large vessel which pierces the pelvic fascia, and passes backwards, between the lumbo-sacral trunk and the first sacral nerve. It leaves the pelvis through the upper part of the greater sciatic foramen, above the piriformis muscle, and enters the buttock, where it divides, under cover of the gluteus maximus and between the adjacent borders of the piriformis and gluteus medius muscles, into superficial and deep branches.
(a) The superficial branch divides at once into numerous rami, some of which supply the gluteus maximus, whilst others pass through it, near its origin, to the overlying skin. The branches freely anastomose with branches of the inferior gluteal, internal pudendal, medial circumflex, deep circumflex iliac, and lateral sacral arteries.
(b) The deep terminal branch, accompanied by the superior gluteal nerve, runs forwards between the gluteus medius and minimus, and, after giving a nutrient branch to the ilium, subdivides into upper and lower branches. The upper branch, runs forwards along the origin of the gluteus minimus from the anterior curved line of the ilium, and passes beyond the anterior margins of the gluteus medius and minimus to anastomose, under cover of the tensor fascia latæ, with the ascending branch of the lateral circumflex artery. It anastomoses with the deep circumflex iliac artery also, and it supplies muscular branches to the adjacent muscles. The lower branch passes more directly forwards, across the gluteus minimus, towards the trochanter major, along with the branch of the superior gluteal nerve which supplies the tensor fascia latæ. It supplies the gluteal muscles, and anastomoses with the ascending branch of the lateral circumflex artery.
Before leaving the pelvis the gluteal artery gives muscular branches to the pelvic diaphragm and the obturator internus, small neural branches to the roots of the sacral plexus, and nutrient branches to the hip-bone.
BRANCHES OF THE ANTERIOR DIVISION.
The anterior division gives off both parietal and visceral branches, and is continued as the umbilical artery. The parietal branches are the obturator, the internal pudendal, and the inferior gluteal. The visceral branches include the superior and inferior vesical, and the middle hæmorrhoidal arteries in the male. In the female the anterior division of the hypogastric artery gives off similar visceral branches, and, in addition, a uterine and a vaginal branch.
1. Arteria Vesicalis Superior. The superior vesical artery arises from the incompletely obliterated posterior part of the umbilical artery, as it lies at the side of the bladder. It passes medially to the upper part of the urinary bladder and divides into numerous branches which anastomose with the other vesical arteries, and it also gives small branches to the urachus, and often to the lower part of the ureter. It may in addition give off a middle vesical branch, and not infrequently the long slender artery to the ductus deferens arises from it.
2. Arteria Umbilicalis.-Atrophy of that portion of the umbilical artery which extends from the anterior division of the hypogastric to the umbilicus has already been referred to. The atrophy is complete between the umbilicus and the origin of the superior vesical artery, but between that origin and the apparent ending of the hypogastric in its two divisions it is incomplete, and the lumen of the vessel, though greatly diminished in size, remains patent. It is from the incompletely obliterated portion that the superior vesical artery arises. The completely obliterated part of the umbilical artery is reduced to a fibrous cord which runs along the side of the bladder to its apex, and then ascends, on the posterior surface of the anterior abdominal wall, to the umbilicus. In the latter part of its course it is known as the ligamentum umbilicale laterale. As it passes along the wall of the pelvis it is external to the peritoneum, and it is crossed by the ductus deferens in the male, and by the round ligament in the female.
3. Arteria Vesicalis Inferior.-The inferior vesical artery runs medially, upon the upper surface of the levator ani, to the base of the bladder. It also gives branches to the seminal vesicles, the ductus deferens, the lower part of the ureter and the prostate, and it anastomoses with its fellow of the opposite side, with the other vesical arteries, and with the middle hæmorrhoidal artery.
4. Arteria Deferentialis.—The artery to the ductus deferens may arise from either the superior vesical or the inferior. It is a long slender vessel which accompanies the ductus deferens to the testis, where it anastomoses with the testicular artery. It also anastomoses with the external spermatic branch of the inferior epigastric artery.
5. Arteria Hæmorrhoidalis Media. The middle hæmorrhoidal artery is an irregular branch which arises either directly from the anterior division of the internal iliac or from the inferior vesical branch; more rarely it springs from the internal pudendal artery. It runs medially, and is distributed to the muscular coats of the rectum; it also gives branches to the prostate, the seminal vesicle, and the ductus deferens, and it anastomoses with its fellow of the opposite side, with the inferior vesical, and with the superior and inferior hæmorrhoidal arteries.
6. Arteria Vaginalis.-The vaginal artery may arise either directly from the anterior division of the hypogastric or from a stem common to it and the uterine artery, and it may be represented by several branches.
It runs downwards and medially, on the floor of the pelvis, to the side of the vagina, and divides into numerous branches which ramify on the anterior and posterior walls of the passage. The corresponding branches of opposite sides anastomose and form anterior and posterior longitudinal vessels, the so-called azygos arteries. They also anastomose above with the cervical branches of the uterine artery, and below with the perineal branches of the internal pudendal. In addition to supplying the vagina, small branches are given to the bulb of the vestibule, to the base of the bladder, and to the rectum.
7. Arteria Uterina.-The uterine artery arises from the anterior division of the internal iliac, either separately or in common with the vaginal or middle hæmorrhoidal arteries. It runs medially and slightly forwards, upon the upper surface of the levator ani, to the lower border of the broad ligament, between the two layers of which it passes medially, and arches above the ureter about threequarters of an inch from the uterus. It passes above the lateral fornix of the vagina to the side of the neck of the uterus, and then ascends towards the fundus, but at the level of the uterine tube it turns laterally, below the tube and between the layers of the broad ligament, and anastomoses with the ovarian artery. It supplies the uterus, the upper part of the vagina, the medial part of the uterine tube, and gives branches to the round ligament of the uterus. It anastomoses with its fellow of the opposite side, and with the vaginal, the ovarian, and the inferior epigastric arteries, along the round ligament of the uterus.
PARIETAL BRANCHES OF THE ANTERIOR DIVISION.
1. Arteria Obturatoria.-The obturator artery (Figs. 774 and 777) runs anteriorly and downwards along the lateral wall of the pelvis minor, just below
its upper margin, to the obturator foramen, through the upper part of which it passes. It terminates, immediately on entering the thigh, by dividing into anterior and posterior terminal branches, which skirt round the margin of the obturator foramen deep to the obturator externus muscle. It is accompanied, in the whole of its course, by the obturator nerve and vein, the nerve being above the artery and the vein below it.
To its lateral side is the pelvic fascia, which intervenes between it and the upper part of the obturator internus muscle, whilst on its medial side it is covered by peritoneum. The ureter intervenes between the posterior part of the artery and the peritoneum. When the bladder is distended it also comes into close relation with the lower and anterior part of the artery. In the female the ovarian vessels and the broad ligament form the medial relations of the obturator artery.
Branches. All the branches except the terminal are given off before the artery leaves the pelvis. They include :-(a) Muscular branches to the obturator internus, levator ani and ilio-psoas muscles. (b) A nutrient branch to the ilium, which passes deep to the ilio-psoas muscle, supplies the bone, and anastomoses with the ilio-lumbar artery. (c) A vesical branch or branches pass medially to the bladder beneath the lateral false ligament. (d) A pubic branch ascends on the posterior surface of the pubis, and anastomoses with its fellow of the opposite side and with the pubic branch of the inferior epigastric. It is given off just before the artery leaves the pelvis, and, in its upward course, it may pass either on the lateral or medial side of the external iliac vein, whilst not infrequently it runs on the medial side of the femoral ring. In the latter case it is important in relation to femoral hernia; this importance is emphasised when, as sometimes happens, the obturator artery arises as an enlarged pubic branch of the inferior epigastric artery instead of from the hypogastric. (e) Terminal. — The anterior terminal branch runs forwards, and the posterior backwards around the margin of the obturator foramen. They lie on the obturator membrane, under cover of the obturator externus, and they anastomose together at the lower margin of the foramen. Both give off offsets which anastomose with the medial circumflex artery, and twigs of supply to the adjacent muscles. The posterior branch also gives an acetabular branch to the hip-joint, which passes upwards, through the acetabular notch on the medial side of the transverse ligament, to supply the ligamentum teres and the head of the femur.
2. Arteria Pudenda Interna. -The internal pudendal artery (Figs. 774 and 775) arises from the anterior division of the hypogastric, close to the origin of the inferior gluteal artery, which slightly exceeds it in size. It runs downwards and backwards, to the lower part of the greater sciatic foramen, lying anterior to the piriformis muscle and the sacral plexus, from both of which it is separated by the pelvic fascia. At the lower border of the piriformis it pierces the pelvic fascia, passes between the piriformis and coccygeus muscles, and leaves the pelvis to enter the buttock. It is accompanied by venæ comites, the inferior gluteal vessels and nerves, the pudendal nerve, and the nerve to the obturator internus. In the buttock it lies on the spine of the ischium, under cover of the gluteus maximus, and between the pudendal nerve and the nerve to the obturator internus, the former being medial to it. It next passes through the lesser sciatic foramen and enters the perineum, in the anterior part of which it terminates by dividing into the profunda artery of the penis and the dorsal artery of the penis.
In the first part of its course in the perineum the artery lies in the lateral fascial wall of the ischio-rectal fossa, where it is enclosed in a canal in the fascia (Alcock's canal). This canal, which is situated about one and a half inches above the lower margin of the tuberosity of the ischium, contains also the pudendal veins and the terminal parts of the pudendal nerve, viz., the dorsal nerve of the penis, which lies above the artery, and the perineal division, which lies below the vessel From the ischio-rectal fossa the internal pudendal artery is continued forwards between the two layers of the fascia of the urogenital diaphragm (O.T. triangular ligament of the urethra), and close to the ramus of the pubis. About half-aninch below the arcuate ligament it turns somewhat abruptly forwards, pierces the inferior fascia of the urogenital diaphragm, and immediately divides into its terminal branches, viz., the profunda artery and the dorsal artery of the penis.
The division sometimes takes place whilst the artery is still between the layers of the urogenital diaphragm.
Branches. In the pelvis it gives small branches to the neighbouring muscles and to the roots of the sacral plexus.
In the buttock. (a) Muscular branches are distributed to the adjacent muscles. (b) Anastomotic branches unite with branches of the superior and inferior gluteal, and medial circumflex arteries.
In the ischio-rectal fossa.-(c) The inferior hæmorrhoidal artery pierces the wall of the fascial canal, and runs obliquely forwards and medially. It soon divides into two or three main branches, which may arise separately from the pudendal; they pass across the space to the anal passage. The artery anastomoses in the walls of the anal passage
FIG. 775.-THE PERINEAL DISTRIBUTION OF THE INTERNAL PUDENDAL ARTERY IN THE MALE.
with its fellow of the opposite side, and with the middle and superior hæmorrhoidal arteries; it anastomoses with the transverse perineal arteries also; and it supplies cutaneous twigs to the region of the anus, and others, which turn round the lower border of the gluteus maximus, to supply the lower part of the buttock.
(d) The perineal artery arises in the anterior part of the ischio-rectal fossa, pierces the base of the fascia of the urogenital diaphragm, and divides into long slender posterior scrotal branches in the male, and posterior labial branches in the female. Those branches are continued forwards, in the urethral triangle, to the scrotum or labium, deep to the superficial perineal fascia. They anastomose with their fellows of the opposite side, with the transverse perineal and the external pudendal arteries, and supply the muscles and subcutaneous structures of the urethral triangle.
(e) The transverse perineal artery is a small branch which arises either directly from the internal pudendal or from its perineal branch. It runs medially along the base of the fascia of the urogenital diaphragm (O.T. triangular lig.) to the central point of the perineum, where it anastomoses with its fellow of the opposite side, with the perineal artery, and with the inferior hæmorrhoidal arteries. It supplies the sphincter ani, the bulbo-cavernosus or sphincter vaginæ, and the anterior fibres of the levator ani.
In the urethral triangle.-(f) The artery to the bulb, a branch which is usually of relatively large size, is given off between the fascial layers of the urogenital diaphragm. It runs transversely along the posterior border of the sphincter of the membranous
urethræ, and then, turning forwards a short distance from the side of the urethra, it pierces the inferior fascia of the urogenital diaphragm and enters the substance of the bulb. It passes onwards in the corpus cavernosum urethra to the glans, where it anastomoses with its fellow and with the dorsal arteries of the penis.
It supplies the sphincter of the membranous urethra, bulbo-urethral gland (Cowper), the corpus cavernosum urethra, and the penile part of the urethra. In the female this artery supplies the bulb of the vestibule.
(g) The profunda artery of the penis (O.T. artery of the corpus cavernosum) in the male, and of the clitoris in the female, is usually the larger of the two terminal branches. Immediately after its origin it enters the crus penis, and runs forwards in the corpus cavernosum penis, which it supplies.
(h) The dorsal artery of the penis in the male, and of the clitoris in the female, passes forwards between the layers of the suspensory ligament, and runs along the dorsal surface of the penis, with the dorsal nerve immediately to its lateral side, whilst it is separated from its fellow of the opposite side by the deep dorsal vein, which lies in the median plane. It supplies the superficial tissues on the dorsal aspect of the penis, sends branches into the corpus cavernosum penis to anastomose with the profunda artery of the penis, and its terminal branches enter the glans penis, where they anasto mose with the arteries to the bulb. It anastomoses also with the external pudendal branches of the femoral.
3. Arteria Gluteal Inferior. The inferior gluteal artery (O.T. sciatic), (Figs. 774 and 776) arises from the hypogastric artery, either separately or by a common trunk with the internal pudendal artery. It descends a little postero-lateral to the internal pudendal vessels, pierces the pelvic fascia, runs backwards between the first and second, or second and third sacral nerves, and, passing between the piriformis and coccygeus muscles, leaves the pelvis through the lower part of the greater sciatic foramen, and enters the buttock just below the piriformis. In the buttock it descends posterior and to the medial side of the sciatic nerve deep to the gluteus maximus, and posterior to the obturator internus, the two gemelli, the quadratus femoris, and upper part of the adductor magnus muscles, to the proximal part of the thigh.
Below the lower border of the gluteus maximus the artery is comparatively superficial, and having given off its largest branches, it runs distally, as a long slender vessel, with the posterior femoral cutaneous nerve.
Branches-In the pelvis.-Small and irregular branches supply the adjacent viscera and muscles and the sacral nerves; they anastomose with branches of the internal pudendal and lateral sacral arteries.
In the buttock. (a) Muscular branches are given off to the muscles of the buttock and to the proximal parts of the hamstring muscles. They anastomose with the internal pudendal, medial circumflex, and obturator arteries. (b) The coccygeal branch arises immediately after the artery leaves the pelvis. It runs medially, pierces the sacro-tuberous ligament and the gluteus maximus, and ends in the soft tissues over the posterior aspect of the lower part of the sacrum and of the coccyx. It gives several branches to the gluteus maximus, and anastomoses with branches of the gluteal and lateral sacra. arteries. (c) An anastomotic branch passes laterally, superficial or deep to the sciatic nerve, towards the greater trochanter of the femur. It anastomoses with branches of the gluteal, internal pudendal, medial and lateral circumflex, and the first perforating arteries, taking part in the formation of the so-called "crucial anastomosis." (d) Cutaneous branches, accompanying twigs of the posterior cutaneous nerve of the thigh, pass round the lower border of the gluteus maximus muscle to the integument. (e) The a. comitans n. ischiadici is a long slender branch which runs distally on the surface, or in the substance of the sciatic nerve. It supplies the nerve, and anastomoses with the perforating arteries and with the termination of the profunda femoris artery.
ARTERIES OF THE INFERIOR EXTREMITY.
The main artery of each lower limb is continued from the corresponding common iliac artery. It descends as a single trunk as far as the lower border of the popliteus, and ends there by dividing into the anterior and posterior tibial arteries. Distinctive names are, however, applied to different parts of the artery, corresponding to the several regions through which it passes. Thus in the abdomen it is