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costal groove the artery lies between the corresponding vein above and the intercostal nerve below, and it terminates anteriorly by anastomosing with an anterior intercostal branch of the internal mammary or of the musculo-phrenic artery. The lower two intercostal arteries, on each side, extend beyond their spaces into the abdominal wall, and anastomose with branches of the superior epigastric, subcostal, and lumbar arteries. The first right aortic intercostal artery frequently gives off the right bronchial artery.

Branches.-(a) The posterior branch passes backwards, accompanied by the posterior branch of a spinal nerve, medial to the anterior superior costo-transverse ligament, between the necks of the ribs which bound the space, and between the adjacent transverse processes, to the vertebral groove, where it divides into a medial and a lateral cutaneous terminal branch. The medial cutaneous branch passes backwards and medially, either over or through the multifidus, giving branches to the muscles between which it passes and to the vertebral column. The lateral branch runs laterally under cover of the longissimus dorsi to the interval between it and the iliocostalis dorsi. It terminates in the skin of the back, after giving branches to the adjacent muscles. Before it divides, each posterior branch gives off muscular branches, and a spinal branch which passes through the corresponding intervertebral foramen, and enters the vertebral canal, to the contents and walls of which it is distributed. The spinal branch divides into three branches-neural, post-central, and pre-laminar. The neural branch divides into two branches which run medially, on the roots of the spinal nerve; they pierce the dura mater and arachnoid, and divide into branches some of which pass to the membranes of the spinal medulla, whilst others are continued on to reinforce the posterior and anterior spinal arteries. The post-central branch divides into ascending and descending branches which, anastomosing with similar branches above and below, form a series of vertical arches on the backs of the bodies of the vertebra. The arches of opposite sides are connected by short transverse anastomoses. The pre-laminar branch is small, and its ascending and descending branches are distributed in a similar though less regular manner on the posterior wall of the vertebral canal.

(6) A collateral branch arises near the angle of the rib. It descends and runs forward along the lower border of the intercostal space, to anastomose in front with an anterior intercostal branch of the internal mammary or musculo-phrenic artery. The collateral branches of the lower two intercostal arteries, on each side, are inconstant ; when present they are small, and terminate in the abdominal wall.

(c) Muscular branches to the adjacent muscles are given off both by the main trunk and its collateral branch.

() A lateral cutaneous offset accompanies the lateral cutaneous branch of the intercostal nerve.

In addition to the secondary branches above-named, the trunk of the first aortic intercostal, on each side, anastomoses with the superior intercostal, and may supply the whole or the greater part of the second intercostal space. The

upper three or four aortic intercostal arteries, on each side, give branches to the mammary gland which anastomose with branches of the lateral thoracic and internal mammary arteries. Longitudinal anastomoses between adjacent trunks and also between adjacent posterior branches of intercostal arteries sometimes exist near the necks of the ribs, or near the transverse processes. These longitudinal anastomoses are of considerable morphological interest.

2. The subcostal arteries are the last pair of parietal branches given off from the thoracic aorta. They are in series with the aortic intercostal arteries, but are situated below the last ribs. Each gives off a posterior branch which behaves in the same manner as the posterior branch of an ordinary aortic intercostal artery. The trunk runs along the lower border of the twelfth rib in company with the last thoracic nerve. It passes below the arcus lumbocostalis lateralis to the abdomen, and there crosses anterior to the quadratus lumborum, and posterior to the kidney and the adjacent part of the colon. It next pierces the aponeurosis of origin of the transversus abdominis, and runs between the transversus and the internal oblique muscles, anastomosing with the lower intercostal arteries, with the lumbar arteries, and with branches of the superior epigastric artery.

3. Superior phrenic branches are given off from the lower part of the thoracie aorta. They are small vessels which ramify on the upper and posterior surfaces of the diaphragm, and anastomose with branches of the pericardiaco-phrenic and musculo-phrenic arteries.

4. The vas aberrans is a variable and inconstant branch of the thoracic aorta ; it represents the dorsal roots of the fourth and sixth right aortic arches of the embryo. When present it arises from the front and right side of the upper part of the descending aorta near the upper left bronchial artery, and passes upwards and to the right behind the esophagus; it frequently anastomoses with the right superior intercostal artery, and it may be enlarged and form the first part of the right subclavian artery.

BRANCHES OF THE ABDOMINAL AORTA. The branches of the abdominal portion of the aorta are distributed almost entirely to the walls and contents of the abdominal cavity, but some supply small branches to the vertebral column, and to the contents of the vertebral canal, and others are prolonged into the pelvis minor. They are divisible into visceral and parietal groups, both of which include paired and single (unpaired) vessels.

Suprarenal.
Paired. Renal.

Inferior phrenic. Visceral.

Paired. Lumbar.
Spermatic or ovarian.

Parietal.
Celiac axis.

Common iliac.
Single. Superior mesenteric.

Single. Middle sacral. Inferior mesenteric.

THE PAIRED VISCERAL BRANCHES OF THE ABDOMINAL AORTA. 1. Arteriæ Suprarenales (Fig. 773).—There are three pairs of suprarenal arteries — the superior, middle, and inferior. Of these the middle only arise directly from the aorta; the superior spring from the inferior phrenic, and the inferior from the renal arteries.

The middle suprarenal arteries are two small branches which arise, posterior to the pancreas, from the sides of the aorta, close to the origin of the superior mesenteric artery. They run, one on each side, laterally and upwards, upon the crura of the diaphragm just above the renal arteries, to the suprarenal glands, to which they are distributed. They anastomose with the superior and inferior suprarenal arteries.

2. Arteriæ Renales.—The renal arteries (Fig. 773) arise, one on each side, from the aorta, about 12 mm. (half an inch) below the origin of the superior mesenteric artery and opposite the second lumbar vertebra.

Both arteries are of large size, and the right is frequently slightly lower in position than the left. Each artery runs almost transversely to the hilum of the corresponding kidney. It passes anterior to the crus of the diaphragm and the upper part of the psoas muscle. The left artery lies posterior to the pancreas; the right vessel passes behind the inferior vena cava, the head of the pancreas, and the descending part of the duodenum. The renal vein usually lies below and anterior to the artery, but near the kidney the vein not infrequently occupies a posterior position.

reaching the hilum of the kidney each artery divides into three branches, two of which pass anterior to the pelvis renalis, and between it and the renal vein, and the third posterior to the pelvis. In the renal sinus these primary branches break up into numerous secondary branches which enter the kidney substance between the pyramids.

Branches.—The following branches are given off by each renal artery, in addition to the terminal branches :

(a) Inferior suprarenal, which passes upwards to the lower part of the suprarenal gland.

(6) Ureteral.–Small branches to the upper part of the ureter, which anastomose with branches of the internal spermatic or ovarian arteries.

(c) Peri-nephric.—Small branches to the fatty capsule of the kidney, which anastomose with the lumbar arteries.

(d) Glandular offsets, either from the main trunk or from some of its branches, pass to the lumbar lymph glands.

3. Arteriæ Spermatica Internæ.—The Internal spermatic arteries are present in both sexes; in the male they are called the testicular arteries and in the female ovarian arteries. In each sex they are long slender vessels which spring from the front of the aorta a short distance below the origins of the renal arteries.

3a. The Testicular Arteries.—Each testicular artery runs downwards and forwards, on the anterior surface of the psoas major, to the abdominal inguinal ring, where it comes into relation with the ductus deferens. It accompanies the ductus deferens through the inguinal canal to the testis, to which it is distributed.

Relations-Posterior.—The right artery passes in front of the inferior vena cava, and as each artery descends, on the anterior surface of the psoas major, it passes in front of the corresponding genito-femoral nerve and the ureter.

Anterior.—Each artery is in relation anteriorly with the peritoneum to which it is attached; but crossing in front of the right artery and intervening between it and the peritoneum are the third or transverse part of the duodenum, the right colic and the ileo-colic arteries, the terminal part of the superior mesenteric artery, and the cæcum. Crossing anterior to the left artery are the left colic and sigmoid branches of the inferior mesenteric artery and the iliac colon.

In the lower part of the abdominal portion of its course each testicular artery is accompanied by two veins, which issue from the pampiniform plexus in the inguinal canal and enter the abdomen through the abdominal inguinal ring, but at a higher level the two veins usually fuse into a single stem.

As it enters the inguinal canal each testicular artery passes in front of the inferior epigastric artery, and the lower end of the external iliac artery; and as it runs downwards and medially, in the canal, it is accompanied by the ductus deferens, and is more or less enclosed in the meshes of the pampiniform venous plexus. At the lower end of the canal it passes through the subcutaneous inguinal ring and descends in the scrotum, lying antero-lateral to the ductus deferens and in close association with the anterior group of testicular veins. At the upper end of the testis it breaks up into branches, some of which are distributed to the testis and others to the epididymis.

Branches.-In the abdominal part of its course each testicular artery gives off :-
(a) Ureteral branches, to the abdominal part of the ureter.
(6) Peri-nephric twigs, to the peri-nephric fat.
(c) Peritoneal branches, which are distributed to the peritoneum.
(d) Glandular branches, which supply blood to the lumbar lymph glands.
Its terminal branches are the testicular and epididymal twigs already mentioned.

3b. Ovarian Arteries.—The course and the relations of each ovarian artery, as far as the level of the brim of the pelvis minor, are the same as the relations of the corresponding testicular artery; but at the level of the upper end of the external iliac artery each ovarian artery turns medially, crosses anterior to the upper end of the corresponding external iliac artery and vein, and enters the upper part of the broad ligament of the uterus. In the broad ligament it runs medially, below the uterine tube, to the level of the ovary. There it turns backwards and passes between the layers of the mesovarium, where it breaks up into terminal branches which enter the ovary through the hilum in its anterior border. As it lies in the broad ligament each ovarian artery is accompanied by the pampiniform plexus of ovarian veins. In the lower portion of the abdominal part of its course it is accompanied by two veins, which issue from the pampiniform plexus at the brim of the pelvis minor, and unite at a higher level into a single trunk.

Branches.-(a) In the abdominal part of its course the branches of the ovarian artery are the same as those of the testicular artery.

In the pelvic part of its course it gives off ::
(a) Tubal branches, to the walls of the uterine tube.
(b) Branches to the round ligament of the uterus.

(C) Uterine branches, which pass towards the uterus to anastomose with the branches of the uterine artery.

THE UNPAIRED OR SINGLE VISCERAL BRANCHES OF THE ABDOMINAL AORTA.

Arteria Cæliaca.--The cæliac artery (Figs. 771 and 773) arises from front of the abdominal aorta, immediately below the aortic orifice of the diaphragm and between its crura. It is a short but wide vessel which runs almost horizontally forwards, for a distance of about 12 mm. (half an inch), and it terminates by dividing into three branches—the left gastric, the hepatic, and the splenic.

Relations.-As the short trunk lies behind the omental bursa it runs forwards, below the caudate lobe of the liver and above the upper border of the pancreas and the splenic vein. It is surrounded by the cæliac plexus of the sympathetic, and has the right cæliac ganglion to its right side and the left coeliac ganglion to its left side.

Branches.—(a) The left gastric (O.T. coronary) is the smallest branch of the coeliac artery. It runs obliquely upwards and to the left, and reaches the lesser curvature of the stomach close to the oesophagus. It then turns sharply forwards, downwards, and to the right, and runs towards the pyloric end of the stomach to anastomose with the right gastric branch of the hepatic artery. In the first part of its course the artery lies posterior to the omental bursa ; it then passes into the left gastro-pancreatic fold, and is continued between the layers of the lesser omentum.

[graphic]

Left gastro-
Cystic artery

epiploic artery
Superior pancreatico-

Splenic artery
duodenal artery

Left gastric artery
Gastro-duodenal artery
Right gastro-epiploic artery

Hepatic artery

Right gastric artery
FIG. 771.—THE CELIAC ARTERY AND ITS BRANCHES.

Branches.—(i.) Esophageal.—When the left gastric artery reaches the stomach it gives off an æsophageal branch which passes upwards, on the æsophagus, and breaks up into branches which anastomose with csophageal branches of the thoracic aorta and with branches of the inferior phrenic. (ii.) Gastric branches are distributed to both surfaces of the stomach. They anastomose with the short gastric branches of the splenic, and with branches of the gastroepiploic arterial arch on the greater curvature of the stomach.

(b) Arteria Lienalis.—The splenic artery (Fig. 771) is the largest branch of the coeliac artery. It runs a tortuous course behind the stomach and the omental bursa, and along the upper border of the pancreas. It lies anterior to the left suprarenal gland and the upper end of the left kidney, and passes forwards between the two layers of the lieno-renal ligament, in which it divides into from five to eight terminal branches which enter the hilum of the spleen and supply the splenic substance. It is accompanied by the splenic vein, which lies below it.

Branches.—(i.) Pancreatic.—Numerous small branches are given off to the pancreas. A larger branch (pancreatica magna), occasionally present, enters the upper border of the pancreas, about the junction of its middle and left thirds, and runs from left to right in the substance of the pancreas, a little above and posterior to the pancreatic duct. Both the small and large arteries supply the substance of the pancreas, and anastomose with one another and with branches of the pancreaticoduodenal arteries. (ii.) The short gastric branches (O.T. vasa brevia), four or five in number, are given the flexor digitorum profundus, and the transverse carpal ligament (0.T. anterior annular). Volar.On its volar aspect it is crossed, in the oblique part of its course, by the pronator teres, the median nerve, which is separated from the artery by the deep head of the pronator teres, the flexor digitorum sublimis, the flexor carpi radialis, and the palmaris longus. In the middle third of the forearm it is overlapped by the volar border of the flexor carpi ulnaris, and in the distal third it is covered by skin and fasciæ only. A short distance proximal to the wrist the palmar cutaneous branch of the ulnar nerve lies volar to it, and as it crosses the transverse carpal ligament, it is bound down by a fascial expansion from the tendon of the flexor carpi ulnaris. Two venæ comites, which frequently communicate with one another, lie one on each side of the artery. On the radial side there is also, in its distal two-thirds, the flexor digitorum sublimis. On its ulnar side are the flexor carpi ulnaris and the ulnar nerve.

Branches.-(1) The volar ulnar recurrent is a small branch which arises in the cubital fossa, frequently in common with the dorsal ulnar recurrent. It passes proximally, to the anterior aspect of the medial epicondyle, under cover of the pronator teres, and anastomoses with branches of the superior and inferior ulnar collateral arteries.

(2) The dorsal ulnar recurrent branch, larger than the volar, arises in the cubital fossa, from the ulnar side of the ulnar artery, and ascends, on the brachialis and under cover of the muscles which arise from the medial epicondyle, to the posterior aspect of that prominence, where it passes between the humeral and olecranoid heads of the fexor carpi ulnaris, and anastomoses with the superior and inferior ulnar collateral arteries. It gives branches to the adjacent muscles and to the elbow-joint.

(3) The common interosseous artery, a short trunk which springs from the radial and dorsal aspect of the ulnar artery, in the distal part of the cubital fossa. It passes dorsally, towards the proximal border of the interosseous membrane, and divides into volar and dorsal interosseous branches.

(3a) The volar interosseous artery runs distally, on the volar surface of the interosseous membrane, between the adjacent borders of the flexor pollicis longus and the flexor digitorum profundus, to the proximal border of the pronator quadratus; there it pierces the interosseous membrane, and continues distally, first on the dorsal surface of the membrane, deep to the extensor pollicis longus and extensor indicis proprius, and then on the dorsal surface of the radius, in the groove for the extensor digitorum communis ; and it terminates, on the dorsum of the carpus, by joining the dorsal carpal arch.

It is accompanied on the volar aspect of the interosseous membrane by the volar interosseous nerve, and, after it has pierced the membrane, by the dorsal interosseous nerve.

Branches.-(a) Nutrient to the radius and ulna; (b) Muscular to the adjacent muscles ; (c) The volar communicating, a slender branch which passes distally, deep to the pronator quadratus and on the volar surface of the interosseous membrane, to anastomose with the volar carpal arch ; (d) Small anastomotic branches are given off, on the dorsum of the forearm, to anastomose with the dorsal interosseous artery ; (e) The median artery (O.T comes nervi mediani) is a long slender branch which arises from the proximal part of the volar interosseous artery and runs with the median nerve to the palm, where it anastomoses with recurrent branches of the superficial volar arch.

(36) The dorsal interosseous artery is usually smaller than the volar interosseous. It passes dorsally between the proximal border of the interosseous membrane and the oblique cord, and then between the supinator and abductor pollicis longus (O.T. ext. oss. met. poll.), after which it runs distally, between the superficial and deep muscles on the dorsum of the forearm, to the wrist. At the wrist it anastomoses with the volar interosseous artery and with the dorsal carpal arch. As it crosses the abductor pollicis longus it is accompanied by the dorsal interosseous nerve, but in the remainder of its course it is separated from the nerve by the deep muscles.

Branches.—a) An interosseous recurrent branch is given off at the dorsal margin of the distal border of the supinator. It runs proximally, on the dorsal surface of the supinator, under cover of the anconeus, to the back of the lateral epicondyle of the humerus, where it anastomoses with the posterior terminal branch of the profunda and with branches of the inferior ulnar collateral artery. (b) Muscular branches to both superficial and deep muscles on the dorsum of the forearm. (c) Cutaneous branches to the skin on the dorsum of the forearm and the wrist.

(4) The volar carpal branch of the ulnar artery is a small branch, given off proximal to the transverse carpal ligament; it passes towards the radial side, deep to the flexor tendons and their sheaths, on the volar surface of the proximal attachments of the volar radio-carpal ligament, and anastomoses with the volar carpal branch of the radial to form the volar carpal arch.

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