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artery, and (ii.) a descending branch to the upper part of the descending colon. The lower branch passes to the left, behind the peritoneum, and divides into upper and lower divisions ; the upper anastomoses with the descending division of the upper branch and supplies the lower part of the descending colon. The lower division supplies the iliac colon, and it anastomoses with the branches of the upper division and with the branches of the sigmoid arteries. Both branches of the left colic artery lie immediately behind the peritoneum, and each branch crosses anterior to the ureter and the internal spermatic vessels.
(6) The sigmoid branches, usually two in number, arise from the convexity of the inferior mesenteric, and pass downwards and to the left to the lower part of the iliac colon and to the pelvic colon. They lie posterior to the peritoneum, and anterior to the psoas major, the ureter, and the upper part of the iliacus. They terminate by dividing into branches which anastomose with the terminal twigs of the lower branch of left colic above and with branches of the superior hæmorrhoidal below, forming a series of arches from which branches are distributed to the lower part of the iliac colon and the pelvic colon.
(c) The superior hæmorrhoidal artery is the direct continuation of the inferior mesenteric. It enters the mesentery of the pelvic colon, crosses the front of the left common iliac artery, descends into the pelvis minor as far as the third piece of the sacrum, or, in other words, the junction between the pelvic colon and the rectum, and divides into two branches which pass downwards on the sides of the rectum. Half-way down the rectum each of the two terminal branches of the superior hæmorrhoidal artery divides into two or more branches which pass through the muscular coats and terminate in the submucous tissue, where they divide into numerous small branches which pass vertically downwards, anastomosing with one another, with offsets from the middle hæmorrhoidal branches of the internal iliac arteries, the inferior hæmorrhoidal branches of the internal pudic arteries, and with branches from the middle sacral artery.
The superior hæmorrhoidal artery supplies the mucous membrane of the pelvic colon and the rectum and the muscular coats of the pelvic colon.
PARIETAL BRANCHES OF THE ABDOMINAL AORTA. 1. Arteriæ Phrenicæ Inferiores.—The inferior phrenic arteries (Fig. 773), right and left, are of small size; they arise, either separately or by a common trunk, from the aorta, immediately below the diaphragm, to which they are distributed. Diverging from its fellow, each artery runs upwards and laterally, on the corresponding crus of the diaphragm—that on the right side passing posterior to the inferior vena cava, that on the left side posterior to the wesophagus—and just before reaching the central tendon of the diaphragm each divides into medial and lateral terminal branches. The medial branch runs forwards and anastomoses
of the opposite side, forming an arch, convex forwards, along the anterior border of the central tendon of the diaphragm. Offsets from this arch anastomose with the pericardiaco-pbrenic, musculo-phrenic, and internal mammary arteries. The lateral branch passes laterally towards the lower ribs, and anastomoses with the musculo-phrenic and lower intercostal arteries.
In addition to supplying the diaphragm each inferior phrenic artery gives a superior suprarenal branch, to the suprarenal gland of its own side, and, occasionally, small hepatic branches which pass through the coronary ligament to the liver. Further, the left artery gives æsophageal branches which anastomose with cesophageal branches of the aorta and of the left gastric artery, whilst from the artery of the right side minute branches pass to the inferior vena cava.
2. Arteriæ Lumbales.— The lumbar arteries correspond to the intercostal branches of the thoracic aorta. They are in series with the intercostal arteries; their distribution is very similar; and, like the intercostals, they arise, either separately or by common trunks, from the posterior aspect of the aorta.
There are usually four pairs of lumbar arteries, but occasionally a fifth pair arises from or in common with the middle sacral artery.
From their origins the lumbar arteries pass laterally and posteriorly, across the front and sides of the bodies of the upper four lumbar vertebræ, to the intervals between the adjacent transverse processes, beyond which they are continued int the lateral part of the abdominal wall.
Each artery lies on the body of the corresponding lumbar vertebra. In its backward course, and while still in relation with the vertebral body, it is crossed by the sympathetic trunk, and then, after passing medial to and being protectei by the fibrous arches from which the psoas major muscle arises, it runs behind the muscle and the lumbar plexus. The upper two arteries, on each side, also pass posterior to the crura of the diaphragm. Beyond the interval between the transverse processes of the vertebræ each artery turns laterally and crosses the
quadratus lumborum- the last usually passing anterior to, and the others posterior to the muscle; it then pierces the aponeurosis of origin of the transversus, and proceeds forwards in the lateral abdominal wall, in the interval between the transversus and internal oblique muscles. The lumbar arteries anastomose with one another, with the lower intercostal and subcostal arteries, and with branches of the superior and inferior epigastric and of the deep circumflex iliac and ilio-lumbar arteries.
Fine twigs also pass from the lumbar arteries to the extra-peritoneal fat; these anastomose with corresponding branches from the inferior phrenic and ilio-lumbar arteries, and with small branches from the hepatic, renal, and colic arteries, to form the subperitoneal plexus of Turner.
The abdominal aorta is almost median in position, consequently the right lumbar arteries are scarcely longer than the left. On the right side the arteries pass behind the inferior vena cava, the upper two arteries being separated from that vessel by the right crus of the diaphragm. The upper two right arteries also pass posterior to the cisterna chyli and the lower end of the azygos vein.
Branches:-Dorsal.- Each lumbar artery gives off, opposite the interval between the vertebral transverse processes, a dorsal branch of considerable size. It is analogous with and is distributed like the posterior branch of an aortic intercostal artery (p. 925). Muscular branches are given off, both from the main trunk and its dorsal branch, to the adjacent muscles.
3. Arteria Sacralis Media. The middle sacral artery (Fig. 773) is a single median vessel. It is commonly regarded as a caudal aorta and as the direct continuation of the abdominal aorta. It is, however, of small size, and almost invariably arises from the back of the aorta, about 12 mm. (half an inch) above its bifurcation. It descends, anterior to the lower two lumbar vertebræ and to the sacrum and coccyx, and ends, opposite the tip of the coccyx, by anastomosing with the lateral sacral arteries to form a loop from which branches pass to the coccygeal glomus. Opposite the fifth lumbar vertebra it is crossed, anteriorly, by the left common iliac vein, below which it is covered by peritoneum and coils of small intestine as far as the third segment of the sacrum, and in the rest of its extent it is posterior to the rectum. It is accompanied below by venæ comites, which, however, unite, above, to form a single middle sacral vein.
As it lies anterior to the last lumbar vertebra it gives off on each side a lumbar branch, the arteria lumbalis ima, which is distributed like an ordinary lumbar artery, and as it descends in front of the sacrum it distributes small parietal branches laterally which anastomose with the lateral sacral arteries. The parietal branches usually give off small spinal offsets which enter the anterior sacral foramina. Small and irregular visceral branches pass to the rectum and anastomose with the superior and middle hæmorrhoidal arteries.
ARTERIÆ ILIACÆ COMMUNES. 4. The common iliac arteries (Figs. 773 and 774) are the terminal branches of the abdominal aorta. They commence opposite the middle of the body of the fourth lumbar vertebra a little to the left of the median plane. Each artery passes downwards and laterally, across the bodies of the fourth and fifth lumbar vertebra and the intervening intervertebral fibro-cartilage, and it terminates, at the level of the lumbo-sacral articulation and anterior to the corresponding sacro-iliac joint, by dividing into external iliac and hypogastric (O.T. internal iliac) branches.
The direction of each common iliac is indicated by a line drawn from the bifurcation of the aorta to a point midway between the symphysis pubis and the anterior superior spine of the ilium.
The right artery is a little longer than the left; the former being about 50 mm. (two inches) and the latter 43 mm. (one and three-quarter inches) in length.
Relations.--Anterior.-Both arteries are covered anteriorly by peritoneum, and are separated by it from coils of the small intestine. Communicating branches between the aortic and hypogastric plexuses of the sympathetic pass in front of the arteries, each of which is often crossed, anteriorly, near its termination by the corresponding ureter
. The left artery is crossed, in addition, by the superior hæmorrhoidal vessels.
Posterior.—Behind the artery, of each side, are the bodies of the fourth and fifth lumbar vertebrae, and the intervening intervertebral fibro-cartilage, the sympathetic trunk, and the psoas major muscle. These relationships, however, are much closer on the left side than on the right. The right common iliac, except at its lower end, where it is in contact with the psoas major, is separated from the structures named by the terminations of the right and left common iliac veins and the commencement of the inferior vena cava. The left common iliac, which is not so separated, lies on the medial border of the psoas major. Somewhat deeply placed, in the areolar tissue between the psoas major and the lumbar vertebræ, are the obturator nerve, the lumbo-sacral trunk, and the ilio-lumbar artery, which form posterior relations to the common iliac artery of the corresponding side.
Lateral.—The lateral relations of each artery are coils of small intestine, and the commencement of the inferior vena cava lies to the lateral side of the upper part of the right artery.
Medial.-On the medial side of the right common iliac artery are the right common iliac vein, below, and the left common iliac vein, above. The last-named vein lies on the medial side of the left common iliac artery.
Branches. The external iliac and the hypogastric are the only branches.
The hypogastric artery (0.T. internal iliac) (Figs. 773, 774, and 777) in the fætus is the direct continuation of the common iliac trunk. It supplies numerous branches to the pelvis, runs upwards on the anterior abdominal wall to the umbilicus as the umbilical artery, and is prolonged through the umbilical cord to the placenta. One of its pelvic branches—the inferior glutæal (0.T. sciatic)—is at first the main artery of the inferior extremity, but subsequently another branch is given off which becomes the chief arterial trunk of the lower limb. This branch is the external iliac artery; it soon equals and ultimately exceeds the hypogastrie in size, and it is into these two vessels that the common iliac appears to bifurcate.
When the placental circulation ceases and the umbilical cord is severed, the umbilical part of the hypogastric trunk which extends from the pelvis minor to the umbilicus atrophies, and is afterwards represented almost entirely by a fibrous cord, known as the obliterated umbilical artery. It is only at its proximal end that the atrophied part remains pervious, and there it forms the commencement of the superior vesical artery. The permanent hypogastric is a comparatively short vessel. Owing to the arrangement of some of its branches it appears to end in an anterior and a posterior division, the former of which is to be regarded as the continuation of the vessel, whilst the latter is simply a common stem of origin for some of the branches.
With this explanation the artery may be described in the usual manner.
It arises from the common iliac opposite the sacro-iliac articulation and at the level of the lumbo-sacral articulation, and descends into the pelvis minor, to terminate, as a rule, opposite the upper border of the greater sciatic notch, in two divisions-anterior and posterior—from each of which branches of distribution are given off. The artery measures about 37 mm. (one and a half inches) in length.
Relations. - Anterior. — Each hypogastric artery is covered antero-medially by peritoneum, behind which the corresponding ureter descends along the anterior border of the artery. The pelvic colon crosses from the front to the medial side of the left artery, and the terminal part of the ileum bears the same relation to the right artery.
Posterior to it are the hypogastric vein and the commencement of the common iliac vein ; still more posteriorly are the lumbo-sacral trunk and the sacro-iliac joint.
Lateral.--On its lateral side the external iliac vein separates it from the psoas major muscle, above. At a lower level the obturator nerve, embedded in a mass of fat, intervenes between the hypogastric artery and the lateral wall of the pelvis. On its medial side it is crossed by some of the tributaries of the hypogastric vein, and it is covered by peritoneum.
Branches.—The hypogastric artery supplies the greater part of the pelvic wall and contents, and its branches are distributed also to the buttock and thigh and to the external organs of generation.
All the branches may be given off separately from a single undivided parent trunk, but as a rule they arise in two groups corresponding to the two divisions ia which the artery, under these circumstances, appears to end.
FIG. 774.-HYPOGASTRIC ARTERY AND ITS BRANCHES IN THE FEMALE.
6. Dorsal nerve of clitoris.
7. Internal pudendal artery. 3. Vaginal artery.
8. Perineal nerve. 4. Inferior hæmorrhoidal nerve.
9. Superficial perineal artery. 5. Inferior hæmorrhoidal artery.
10. Artery to the bulb of the vestibule.
BRANCHES OF THE POSTERIOR DIVISION. The posterior terminal division gives off the ilio-lumbar and lateral sacral arteries, and is continued as the superior glutæal artery.
1. Arteria Ilio-lumbalis.—The ilio-lumbar artery runs upwards and laterally, across the upper margin of the pelvis minor, to the iliac fossa. It passes anterior to the sacro-iliac articulation, between the lumbo-sacral trunk and the obturator nerve, and posterior to either the lower part of the common or the upper part of the external iliac vessels, and the psoas and iliacus muscles.
In the iliac fossa it divides into an iliac and a lumbar branch. The iliac branch anastomoses with branches of the deep circumflex iliac and obturator arteries, it gives offsets to the iliacus, and supplies a large nutrient branch to the ilium. A lumbar branch ascends, behind the psoas major, to the crest of the ilium. It supplies the psoas and quadratus lumborum, and anastomoses with the lumbar and deep