A Laboratory Manual of the Anatomy of the Rat/The Vascular System (Continued further)
THE VASCULAR SYSTEM (Continued)
VEINS POSTERIOR TO THE HEART[1]
Blood from the parts of the rat posterior to the heart enters the right auricle through the inferior vena cava (post cava). Trace the vena cava caudally to the diaphragm, which it pierces, then enters the abdominal cavity. In the thoracic cavity the vein is surrounded by the lobes of the lungs, and lies at the right of the esophagus.
Study the structure and attachments of the diaphragm. It comprises a central V-shaped tendinous portion, surrounding which is a muscular region with fibers radiating from the central tendon to the adjacent body walls. Note the relative positions of the apertures through which the inferior vena cava, esophagus, and descending aorta penetrate the diaphragm. Observe the number and distribution of the phrenic veins which traverse the diaphragm, carrying blood from its substance to the inferior vena cava. Follow the inferior vena cava posteriorly from the diaphragm, exposing its tributaries, which are described below.
The hepatic veins convey the blood from the liver, which received it from the portal circulation and hepatic artery, to the inferior vena cava. The hepatic veins may be exposed by carefully chipping away the brittle tissue of the liver with a blunt instrument. Determine the number and location of these veins. The two renal veins, short but of large calibre, drain the blood from the kidneys into the inferior vena cava. As the right kidney lies anterior to the left, so the right renal vein joins the inferior vena cava anterior to the left renal. Locate and trace the suprarenal veins, which drain the suprarenal glands. The two ovarian veins pass from the vicinity of the ovary, along the broad ligament of the uterus, in company with the ovarian arteries, thence along the dorsal side of the abdominal cavity. The left ovarian vein joins the left renal vein, the right ovarian opens into the inferior vena cava some distance caudad to the right renal vein. Do you find spermatic veins corresponding in general location to the ovarian veins? In other mammals, the cat and man for instance, right and left spermatic veins are present which open into the inferior vena cava and left renal veins, respectively. The right and left iliolumbar veins join the inferior vena cava in the lumbar region. They accompany the corresponding iliolumbar arteries. Follow the course of each vein from its mouth caudolaterally across the dorsal surface of the abdominal cavity.
Trace the inferior vena cava caudally to the region where it is formed by the confluence of the right and left common iliac veins. Follow each common iliac distally to its bifurcation into the external iliac and hypogastric (internal iliac) veins. The latter may be traced dorsally into the mass of muscle, then posteriorly close to the median surface of the pelvic girdle. The external iliac vein gives off several branches, one of which, the femoral vein, accompanies the femoral artery along the inner portion of the thigh. Note any veins which carry blood away from the urogenital organs. Locate the junction of the middle sacral vein with the dorsal side of the inferior vena cava near the union of the latter with the common iliac veins. Trace the caudal vein posteriorly through the pelvic region ventral to the sacrum. Carefully clear away the tissues in which the inferior vena cava is imbedded and find the lumbar veins , which join the dorsal side of the inferior vena cava. Note their number, position, and distribution.
Exercise XXV. Make a full-page drawing of the veins anterior and posterior to the heart, incorporating the sketch required by Exercise XIV.
ARTERIES POSTERIOR TO THE HEART
The descending aorta is the posterior continuation of the aortic arch. It courses caudally through the thorax and abdomen, ventral to the vertebral column, carrying blood to the body walls, viscera, hind limbs, etc. Its position and conspicuous size make its identification easy. The main branches are as follows, beginning at the anterior end of the series.
The paired intercostal arteries pass dorsally from the thoracic section of the aorta to the muscles between the ribs. Determine the number, arrangement, and distribution of these arteries.
The first large artery leaving the dorsal aorta after it enters the abdominal cavity is the coeliac. Passing ventrally, this divides into three branches: the splenic, the hepatic, and left gastric arteries. The splenic artery splits into several branches which terminate in the spleen. It sends smaller rami to the pancreas and stomach. The hepatic artery, some distance from its origin, delivers blood to the following branches. The right gastric artery goes to the region of the pylorus, thence along the lesser curvature of the stomach, and anastomoses with the left gastric artery, which is described below. The right gastro-epiploic artery passes to the greater curvature of the stomach. The superior pancreatico-duodenal artery courses along the duodenum, to which it sends branches. The right gastro-epiploic and superior pancreatico-duodenal arteries may arise from the hepatic artery by a short gastro-duodenal artery. Still another branch supplies the pancreas. After giving off the above vessels, the hepatic artery passes anteriorly and breaks up into several branches which enter the liver. The left gastric artery runs to the lesser curvature of the stomach. A large terminal branch supplies the dorsal surface of the stomach, another goes to the ventral surface of this organ. Small vessels are given off to the esophagus. A small branch traverses, to the right, the lesser curvature of the stomach, and anastomoses with the right gastric artery, as previously mentioned. Determine the variability of the branches of the coeliac.
The superior mesenteric artery leaves the dorsal aorta a short distance posterior to the coeliac in the region of the renal arteries. It sends numerous branches through the mesenteries to all the divisions of the small intestine, to the caecum, and the colon. The branch to the colon joins the inferior mesenteric artery.
The two large renal arteries carry blood from the dorsal aorta to the kidneys. The right renal supplies the right kidney, the left renal the left kidney. Each renal artery gives off anteriorly a suprarenal artery to the suprarenal gland on the same side.
The two spermatic arteries of the male rat leave the dorsal aorta a short distance caudad to the renals and course posteriorly along the dorsal surface of the abdominal cavity. The right spermatic finally enters the right testis, the left spermatic artery the left testis. Expose each artery throughout its length. The two ovarian arteries of the female similarly supply the ovaries. They correspond in position to the spermatic arteries of the male. Each ovarian artery anastomoses with the uterine artery, which runs parallel to the horn of the uterus in the broad ligament. Trace the uterine artery caudally to its origin.
The two iliolumbar arteries pass laterally in the lumbar region from the dorsal aorta, along the dorsal surface of the abdominal cavity, giving off branches to the muscles of the back. Trace the terminal branches.
The inferior mesenteric artery branches from near the posterior end of the dorsal aorta, sends branches to the rectum and descending colon, passes anteriorly along the latter, and anastomoses with the superior mesenteric artery. Is this anastomosis always present?
The aorta bifurcates at its posterior extremity, forming the right and left common iliac arteries. These give off dorsal branches to the muscles of the back, then divide into the external and internal iliac (hypogastric) arteries. The latter, which runs dorsally, divides into two main branches, one which passes laterally to the proximal region of the thigh, while the other passes caudally through the pelvic region. Dissect out these branches. The external iliac artery passes to the median surface of the thigh, there becoming the femoral artery. This gives off the saphenous artery, then penetrating the thigh it courses distally to the foot, supplying branches to the muscles of the thigh and shank. Trace the saphenous along the median surface of the shank, and note that its terminal branches enter the foot.
The middle sacral artery arises from the dorsal aorta near its posterior end and proceeds caudally through the pelvic region into the tail. Trace it and observe its branches.
The unpaired lumbar arteries pass dorsally from the abdominal section of the dorsal aorta. They correspond to the intercostal arteries of the thoracic region. The lumbar arteries bifurcate ventral to the vertebral column, the branches of each artery proceding dorsally on each side of the column. Determine the number of lumbar arteries, and follow them into the dorsal musculature of the lumbar region.
Exercise XXVI. Make a full-page drawing of the arteries anterior and posterior to the heart, incorporating the sketch required by Exercise XV.
- ↑ Locate the sympathetic nervous system before dissecting the arteries and veins posterior to the heart. This system will probably be injured during the dissection.