Part 173

1. The =gastric artery= (A. gastrica sinistra) passes downward and forward in the gastro-phrenic ligament, gives off œsophageal and pancreatic branches, and divides above and behind the cardia into anterior and posterior branches.

(a) The =anterior branch= (Ramus cranialis) crosses the lesser curvature just to the right of the cardia and ramifies on the parietal surface of the stomach. The branches pursue a flexuous course toward the greater curvature and anastomose with the short gastric arteries and the gastric branch of the hepatic artery.

(b) The =posterior branch= (Ramus caudalis) is distributed in a similar fashion on the visceral surface.

(c) The =œsophageal branch= (Ramus œsophageus) passes through the hiatus œsophageus into the thoracic cavity above the œsophagus and anastomoses with the œsophageal branch of the broncho-œsophageal artery.

FIG. 449.—PLAN OF CHIEF BRANCHES OF ANTERIOR MESENTERIC ARTERY OF HORSE.

1, Stump of anterior mesenteric artery; 2, stumps of arteries of small intestine; 3, external cæcal artery, 4, internal cæcal artery; 5, ileal artery; 6, ventral colic artery; 7, dorsal colic artery; 8, middle colic or first artery of small colon. ]

The gastric artery often arises by a common trunk with the splenic. The two terminal branches may arise separately, or the anterior from the splenic and the posterior from the hepatic. The œsophageal branch often arises from the splenic or the posterior gastric.

FIG. 450.—DISSECTION OF SUBLUMBAR REGION, PELVIC INLET, AND INNER SURFACE OF THIGH OF HORSE.

Blood-vessels: 1, Aorta; 2, posterior vena cava; 3, hepatic; 4, gastric; 5, splenic; 6, 7, renal; 8, anterior mesenteric; 9, arteries of small intestine; 10, ileo-cæco-colic; 11, dorsal colic; 12, artery of small colon; 13, posterior mesenteric; 14, external iliac; 15, internal iliac; 16, circumflex iliac; 17, 19, anterior and posterior branches of 16; 18, anastomosis with intercostals; 20, spermatic; 21, cremasteric; 22, lateral sacral; 23, internal pudic; 24, umbilical; 25, femoral; 26, deep femoral; 27, anterior femoral; 28, branch to gracilis; 29, saphenous.

Lymph vessels and glands: a, Lymph vessels; b, lumbar glands; c, internal iliac glands; d, external iliac glands; e, precrural glands; f, deep inguinal glands (position indicated by dotted line).

Nerves and ganglia: 1, 2, Left and right cœliaco-mesenteric ganglia; 3, posterior mesenteric ganglion; 4, connection between 1 and 2; 5, connection between hepatic and splenic nerves; 6, 7, connections between anterior and posterior mesenteric ganglia; 8, splanchnic nerve; 9, lumbar trunk of sympathetic; 10, pelvic branches of posterior mesenteric ganglion; 11, internal spermatic nerve; 12, last thoracic nerve; 13, ilio-hypogastric nerve; 14, anastomosis between 13 and 15, ilio-inguinal nerve; 16, 17, cutaneous and muscular branches of 15; 18, 19, muscular and scrotal branches of external spermatic nerve; 20, external cutaneous nerve of thigh; 21, femoral nerve; 22, saphenous nerve; 23, branch of 22 to sartorius.

A, Cut surface of obliquus abdominis externus; B, cut surface of obliquus abdominis internus; C, depression due to disappearance of fat in interval between outer border of psoas major and iliacus; D, thick part of iliac fascia which extends from tendon of psoas minor to external angle of ilium; E, superficial fascia of flank; F, internal inguinal ring; G, external inguinal ring; H, patella; I, femoral canal; J, semimembranosus; K, suspensory ligaments of penis; L, cross-section of penis; M, stump of spermatic cord; N, ilio-psoas; O, tensor fasciæ latæ; P, P, extremities of external angle of ilium; Q, remains of iliac fascia; R, ilio-lumbar ligament or deep layer of lumbo-dorsal fascia; S, line of attachment of gastro-pancreatic fold; T, tendon of right crus of diaphragm; U, right crus; V, aorta at hiatus aorticus; W, left crus of diaphragm. The position of the kidneys is indicated by dotted lines. (After Schmaltz, Atlas d. Anat. d. Pferdes) ]

2. The =hepatic artery= (A. hepatica) is larger than the gastric. It passes forward to the right and ventrally on the dorsal surface of the pancreas, covered by the gastro-pancreatic fold, crossing obliquely under the vena cava, and reaches the inner border of the portal vein. It divides into three or four branches which enter the portal fissure of the liver and ramify within the gland with the portal vein and the hepatic duct. It gives off the following collateral branches:

(a) =Pancreatic branches= (Aa. pancreaticæ) are given off as the artery crosses the pancreas, in which it is partly embedded.

(b) The =pyloric artery= (A. gastrica dextra) arises above the first curve of the duodenum. It descends to the pylorus, sending branches to the first part of the duodenum and the pylorus, and anastomoses with the gastric and right gastro-epiploic arteries. It may arise from the gastro-duodenal.

(c) The =gastro-duodenal artery= (A. gastroduodenalis) passes to the second curve of the duodenum and divides into the right gastro-epiploic and the pancreatico-duodenal. The =right gastro-epiploic artery= (A. gastroepiploica dextra) crosses over the posterior surface of the duodenum and enters the great omentum, in which it runs to the left, parallel with the greater curvature of the stomach. It gives branches to the latter and to the omentum and forms an anastomotic arch with the left gastro-epiploic artery. The =pancreatico-duodenal artery= (A. pancreaticoduodenalis) divides into pancreatic and duodenal branches. The former (Ramus pancreaticus) supplies the middle part of the pancreas and is often replaced by a number of variable twigs. The duodenal branch (Ramus duodenalis) passes to the right along the lesser curvature of the duodenum and anastomoses with the first branch of the anterior mesenteric artery.

3. The =splenic artery= (A. lienalis) is the largest branch of the cœliac. It passes to the left (with the large satellite vein) on the left extremity of the pancreas and across the saccus cæcus of the stomach. Entering the suspensory ligament of the spleen, it runs in the hilus of the spleen to the apex, beyond which it is continued as the left gastro-epiploic. It gives off the following branches:

(a) =Pancreatic branches= (Rami pancreatici) to the left extremity of the pancreas.

(b) =Splenic branches= (Rami lienales), which plunge into the substance of the spleen.

(c) =Gastric branches= (Aa. gastricæ breves), which pass in the gastro-splenic omentum to the greater curvature of the stomach, where they bifurcate and anastomose with the gastric arteries.

(d) The =left gastro-epiploic artery= (A. gastroepiploica sinistra) is the continuation of the splenic artery. It passes to the right in the great omentum, parallel with the greater curvature of the stomach, and anastomoses with the right gastro-epiploic. It gives off branches to the greater curvature of the stomach, and twigs to the omentum.

II. The =anterior= or =great mesenteric artery= (A. mesenterica cranialis) arises from the ventral face of the aorta at the first lumbar vertebra. It is a large unpaired trunk, about an inch (ca. 2 to 3 cm.) in length, which passes ventrally between the vena cava and the left adrenal into the root of the great mesentery, when it divides into three branches—left, right, and anterior.

1. The =left branch= gives off at once about fifteen to twenty =arteries of the small intestine= (Aa. intestinales). These come off close together and pass in divergent fashion between the layers of the great mesentery, each dividing into two branches which anastomose with adjacent branches to form a series of arches. In the anterior part of the series secondary arches are formed by the union of branches given off from the primary set of arches. From the convex side of these arches terminal branches pass to the wall of the small intestine, in which they ramify and form a vascular network. They are accompanied by satellite veins and by nerves and lymph vessels. The first artery anastomoses with the pancreatico-duodenal, and the last with the ileal branch of the great mesenteric artery. Branches are supplied to the mesenteric lymph glands.

2. The =right branch= (A. ileo-cæco-colica) might be regarded as the continuation of the trunk. It runs downward and a little forward and to the right and gives off the ileal, the two cæcal, and the ventral colic arteries.

(1) The =ileal= or =ileo-cæcal artery= (A. ilea) passes in retrograde fashion along the terminal part of the ileum and unites with the last branch of the left division.

(2) The =external= or =inferior cæcal artery= (Ramus cæcalis lateralis) passes between the cæcum and the origin of the colon and runs on the external muscular band of the cæcum to the apex, where it anastomoses with the internal artery. Besides numerous collaterals to the cæcum, it gives off the artery of the arch, which passes along the lesser curvature of the base of the cæcum and runs on the outer face of the origin of the great colon.

(3) The =internal= or =superior cæcal artery= (Ramus cæcalis medialis) passes along the inner band to the apex of the cæcum, where it anastomoses with the external cæcal artery.

(4) The =ventral=, =right=, or =direct colic artery= (A. colica ventralis) runs along the opposed surfaces of the ventral (first and second) parts of the great colon to the pelvic flexure, where it unites with the dorsal colic artery. It supplies the ventral parts of the great colon and sends a branch to the base of the cæcum.