D DISTRIBUTION OF THE SUPERIOR MESENTERIC ARTERY. 1. Descending portion of the duodenum. 2. Transverse portion. 3. Pancreas. 4. Jejunum. 5. Ileum. 6. Cæcum and appendix vermiformis. 7. Ascending colon. 8. Transverse colon. 9. Descending colon. 10. Superior mesenteric artery. 11. Colica media. 12. The branch which inosculates with the colica sinistra. 13. Pancreatico-duodenalis inferior. 14. Colica dextra. 15. Ileocolica. 16, 16. Vasa intestini tenuis.

The SPERMATIC ARTERIES (spermaticæ internæ) are two small vessels which arise from the front of the aorta below the superior mesenteric; from their origin each artery passes obliquely outwards, and accompanies the corresponding ureter along the front of the psoas muscle to the border of the pelvis, where it is in relation with the external iliac artery. It is then directed outwards to the internal abdominal ring, and follows the course of the spermatic cord along the spermatic canal and through the scrotum to the testicle, to which it is distributed. The right spermatic artery lies in front of the vena cava, and both vessels are accompanied by veins and by the spermatic plexuses of nerves.

The spermatic arteries in the female (ovarian) descend into the pelvis and pass between the two layers of the broad ligaments of the uterus, to be distributed to the broad ligaments, ovaries, Fallopian tubes, and round ligaments; along the latter they are continued to the inguinal canal and labium at each side. They inosculate with the uterine arteries.

The INFERIOR MESENTERIC ARTERY (mesenterica inferior), smaller than the superior, arises from the abdominal aorta, about two inches below the origin of the latter vessel, and descends between the layers of the left meso-colon, to the left iliac fossa, where it divides into three branches:

The Colica sinistra (superior) is distributed to the descending colon; it passes upwards and outwards behind the peritoneum, and divides into two branches, one

BRANCHES OF THE INFERIOR MESENTERIC ARTERY.

1, 1. The superior mesenteric, and small intestines turned over to the right side. 2. Cæcum and appendix cæci. 3. Ascending colon. 4. Transverse colon raised upwards. 5. Descending colon. 6. Sigmoid flexure. 7. Rectum. 8. Aorta. 9. Inferior mesenteric artery. 10. Colica sinistra, inosculating with, 11, colica media. 12, 12. Sigmoid branches. 13. Superior hæmorrhoidal artery. 14. Pancreas. 15. Descending portion of the duodenum.

of which (ramus anastomoticus) ascends to inosculate with the colica media, while the other descends to communicate with the sigmoid branch. The inosculation of the colica sinistra with the colica media is the largest arterial anastonosis in the body.

The Sigmoid artery (colica sinistra inferior) passes obliquely outwards behind the peritoneum and divides into branches which form arches, and are distributed to the sigmoid flexure of the colon. The superior branch inosculates with the colica sinistra, the inferior with the superior hæmorrhoidal artery.

The Superior hæmorrhoidal artery is the continuation of the inferior mesenteric. It crosses the ureter and left common iliac artery, and descending between the two layers of the meso-rectum, is distributed to the rectum as far as its middle, anastomosing with the middle and inferior hæmorrhoidal arteries.

The SUPRA-RENAL (suprarenales; capsulares) are two small vessels which arise from the aorta immediately above the renal arteries, and are distributed to the supra-renal capsules. They are sometimes branches of the phrenic or of the renal arteries.

The RENAL ARTERIES (renales; emulgentes) are two large trunks given off from the sides of the aorta immediately below the superior mesenteric artery; the right is longer than the left, on account of the position of the aorta, and passes behind the vena cava to the kidney of that side. The left is somewhat higher than the right. They divide into several large branches previously to entering the kidney, and ramify very minutely in its vascular portion. The renal arteries supply several small branches to the supra-renal capsules, and one to the ureter. The LUMBAR ARTERIES (lumbales) correspond with the intercostals in the chest; they are four or five in number at each side, curve around the bodies of the lumbar vertebræ beneath the psoas muscles, and divide into two branches; one, dorsal branch, passes backwards between the transverse processes, and is distributed to the vertebræ and spinal cord and muscles of the back; the other, parietal branch, taking its course behind the quadratus lumborum, supplies the abdominal muscles, and inosculates with branches of the internal mammary and epigastric artery. The first lumbar artery runs along the lower border of the last rib; the last, along the crest of the ilium. In passing between the psoas muscle and the vertebræ, they are protected by a series of tendinous arches, which defend them and the communicating branches of the sympathetic nerve from pressure, during the action of the muscle.

The SACRA MEDIA arises from the posterior part of the aorta at its bifurcation, and descends along the middle of the anterior surface of the sacrum to the first piece of the coccyx, where it terminates by inosculating with the lateral sacral arteries. It distributes branches to the rectum and anterior sacral nerves, and inosculates at either side with the lateral sacral arteries.

Varieties in the Branches of the Abdominal Aorta.-The phrenic arteries are very rarely both derived from the aorta. One or both may be branches of the coeliac axis; one may proceed from the gastric artery, from the renal, or from the upper lumbar. There are occasionally three or more phrenic arteries. The coeliac axis is variable in length, and gives off its branches irregularly. There are sometimes two or even three hepatic arteries, one of which may be derived from the gastric or from the superior mesenteric. The colica media is sometimes derived from the hepatic artery. The spermatic arteries are variable both in origin and number. The right spermatic may be a branch of the renal; the left, of the inferior mesenteric. The supra-renal arteries may be derived from the phrenic or renal arteries. The renal arteries present several varieties in number; there may be three or even four on one side, and one only on the other. When there are several renal arteries on one side, one may arise from the common iliac artery, from the front of the aorta near its lower part, or from the internal iliac.

COMMON ILIAC ARTERIES.

The abdominal aorta divides opposite the fourth lumbar vertebra into the two common iliac arteries. Sometimes the bifurcation takes place as high as the third, and occasionally as low as the fifth. The common iliac arteries (iliacæ communes vel primitive) are about two inches in length; they diverge from the termination of the aorta, and pass downwards and outwards at each side to the margin of the pelvis, opposite the sacro-iliac symphysis, where they divide into the internal and external iliac. In old persons the common iliac arteries are more or less dilated and curved in their course. The right artery is somewhat longer than the left, and forms a more obtuse angle with the termination of the aorta; the angle of bifurcation is greater in the female than in the male.

Relations. The relations of the two arteries are different at the two sides of the body. The right common iliac is in relation in front with the peritoneum, and is crossed at its bifurcation by the ureter. It is in relation behind with the two common iliac veins, and externally with the psoas magnus. The left is in

relation in front with the peritoneum, and is crossed by the rectum and superior hæmorrhoidal artery, and, at its bifurcation, by the ureter. It is in relation behind with the left common iliac vein, and externally with the psoas magnus.

INTERNAL ILIAC ARTERY.

The Internal iliac artery (iliaca interna; hypogastrica), is a short trunk, varying in length from an inch to two inches. It descends obliquely forwards to a point opposite the upper margin of the great sacro-ischiatic foramen, where it divides into an anterior and a posterior trunk. In the foetus, the internal iliac artery under the name of hypogastric or umbilical is continued onwards by the side of the fundus of the bladder to near its apex, whence it ascends by the side of the linea alba and urachus to the umbilicus, where it becomes the true umbilical artery. After birth, this artery ceases to be pervious beyond the side of the bladder, and the obliterated portion is converted into a fibrous cord. The projection of the two cords on the inner wall of the abdomen causes the depression at each side, which goes by the name of peritoneal fossa.

Relations. This artery rests externally on the sacral plexus and origin of

ILIAC ARTERIES.

1. Aorta. 2. Left common iliac artery. 3. External iliac. 4. Epigastric artery. 5. Circumflexa ilii. 6. Internal iliac artery. 7. Its anterior trunk. 8. Its posterior trunk. 9. The pervious portion of the umbilical artery giving off (10) the superior vesical artery. 11. Internal pudic artery passing behind the spine of the ischium (12) and lesser sacro-ischiatic ligament. 13. Middle hæmorrhoidal artery. 14. Ischiatic artery, also passing behind the anterior sacro-ischiatic ligament to escape from the pelvis. 16. Iliolumbar, ascending to inosculate with the circumflexa ilii artery (5) and form an arch along the crest of the ilium. 17. Obturator artery. 18. Lateral sacral. 19. Gluteal artery passing through the upper part of the great sacro-ischiatic foramen. 20. Sacra media. 21. Right common iliac artery cut short. 22. Femoral artery.

the pyriformis muscle; posteriorly it is in relation with the internal iliac vein, and anteriorly with the ureter.

Branches. The branches of the anterior trunk are, the

Branches of the Anterior Trunk

The Superior vesical arteries are three or four small branches, which proceed from the pervious portion of the umbilical artery. They are distributed to the upper and middle part of the bladder. From one of these there passes off a small artery, the deferential, which accompanies the vas deferens along the spermatic cord.

The Inferior vesical, somewhat larger than the preceding, passes down upon the side of the bladder to its base, and is distributed to that region, the vesiculæ seminales, and prostate gland.

The Middle hæmorrhoidal artery, frequently a branch of the preceding, passes downwards to the rectum, to which it is distributed, inosculating with the superior and inferior hæmorrhoidal arteries. In the female it distributes branches to the vagina.

The Uterine artery passes inwards between the layers of the broad ligament to the neck of the uterus, and ascends in a tortuous course along its lateral border. It gives branches to the vagina, lower part of the bladder, Fallopian tube (tubaria), ovary (ovaria), and round ligament, and inosculates with the spermatic or ovarian artery. According to Weber the ovarian branch of the uterine is the special artery of the ovary.

The Vaginal artery corresponds in position with the inferior vesical, and is distributed to the vagina, and neighboring parts of the bladder and rectum.

The OBTURATOR ARTERY (obturatoria; arising frequently from the posterior trunk of the internal iliac) passes forwards from the anterior trunk, a little below the brim of the pelvis, to the upper border of the obturator foramen. Escaping from the pelvis through a tendinous arch formed by the obturator membrane, it divides into two branches, internal and external.

Its branches within the pelvis are: an iliac branch, which supplies the bone of the iliac fossa, and inosculates with the ilio-lumbar artery; and a pubic branch which is given off close to the obturator foramen, and inosculates with its fellow of the opposite side, behind the pubes, and with the pubic branch of the epigastric artery.

The internal branch curves inwards around the bony margin of the obturator foramen, and distribute twigs to the obturator and adductor muscles, inosculating with the internal circumflex artery of the femoral.

The external branch winds around the outer margin of the obturator foramen to the space between the gemellus inferior and quadratus femoris, where it in osculates with the ischiatic artery. In its course it inosculates also with the internal circumflex, and sends a small branch through the notch in the aceta bulum (ramus acetabuli) to supply the ligamentum teres.

The ISCHIATIC ARTERY (ischiadica; glutæa inferior) is the larger of the twe terminal branches of the anterior division of the internal iliac. It passes downwards in front of the pyriformis and sacral plexus of nerves, lying internally to the pudic artery, to the lower part of the great ischiatic foramen, where it escapes from the pelvis between the inferior border of the pyriformis and coccygeus. It then descends in the space between the trochanter major and tuberosity of the ischium in company with the ischiatic nerves, and divides into several branches, the principal of which are, coccygeal, comes nervi ischiatici, and muscular.

The Coccygeal branch pierces the great sacro-ischiatic ligament, and is distributed to the coccygeus and levator ani, and to the integument around the anus and coccyx.

The Comes nervi ischiatici is a slender branch, which accompanies the great ischiatic nerve extending as far as the lower part of the thigh.

The Muscular branches supply the muscles of the posterior part of the hip and thigh, and inosculate with the internal and external circumflex arteries,