Introduction

 The major organ systems involved in digestion, respiration, and circulation are similar in many respects to those of more advanced vertebrates. The anatomy of these systems serves to demonstrate features consistent with what has come to be known as the basic body plan of vertebrates.

Digestive System

 Just to the left of the mid-ventral line, make a longitudinal incision extending from the cloaca to the pectoral girdle. Continue by making transverse cuts from the anterior and posterior ends of the incision and reflect the flaps to provide exposure of the peritoneal cavity. Locate the esophagus and identify the esophageal papillae. The esophagus enters the stomach which is divided into cardiac and pyloric regions. The small intestine joins the stomach at the pyloric sphincter as a short segment, the duodenum. The longer and thicker part of the small intestine is the ileum. Incise the ileum and locate the spiral valve. Extending from the ileum to the rectal gland is the colon. The terminal part of the digestive tract is the rectum which extends from the colon to the anus.
 The liver consists of long left and right lobes and a shorter median lobe. Along the right edge of the median lobe, locate the gall bladder and the common bile duct which continues to the doudenum. Expose the pancreas and identify the dorsal and ventral lobes. Along the outer curvature of the stomach is the spleen.
 Covering the surfaces of the digestive organs is the visceral peritoneum which forms the mesenteries. The falciform ligament (suspensory ligament of the liver) extends from the anterior border of the liver to the mid-ventral body wall as a short stub of peritoneum. The following mesenteries should be identified: lessor omentum, mesogaster, gastrosplenic ligament, mesentery proper, and mesorectum.

Respiratory System

To expose the respiratory system, make an incision beginning at the left corner of the mouth and continuing under the gill slits along the body wall to the pectoral girdle. Examine the buccal cavity noting the teeth and tongue. The pharyngeal cavity is characterized by the presence of longitudinal mucosal folds. In the anterolateral wall of the pharynx find the spiracle which represents the first gill slit. Further back on the pharyngeal wall are the five pairs of internal gill slits. Between the internal and external gill slits is the branchial chamber (also known as the gill chamber). Examine an entire holobranch (gill) and note that it includes the entire "arch-shaped" tissue partition between each pair of gill chambers. Each holobranch consists of an interbranchial septum of connective tissue which supports two vascular folds, the demibranchs. Note that anterior to the first gill chamber there is only a single demibranch. A pseudobranch is associated with the spiricle. The vascular folds which compose each demibranch are made up of gill lamellae (gill filaments). The interbranchial septum is supported by cartilagenous spines, the gill rays, while those spines which face into the pharynx are the gill rakers.

Circulatory System

 After you have examined the pharynx, carefully remove the skin from the ventral surface of the head to the pectoral girdle. Reflect the common coracoarcural muscles and continue the incision to intersect with the abdominal incision made previously. Deep to the coracoarcurals and pectoral girdle, locate the pericardium. The pericardium consists of parietal and visceral layers. Open the pericardial sac and expose the heart. The heart consists of a single atrium and ventricle. The atrium receives blood from the sinus venosus which lies next to the transverse septum. Anteriorly, the ventricle gives rise to a muscular tube, the conus arteriosus. Note the coronary arteries which supply blood to the heart. Coming off of the conus arteriosus is the single median ventral aorta which gives off pairs of afferent branchial arteries to each gill arch.

 Next remove the mucosal epithelium from the roof of the mouth and pharynx. Locate the efferent branchial arteries and note that each forms from the union of a pretrematic and a posttrematic artery. Also locate the esophageal arteries and the subclavian arteries which supply blood to the pertoral fins and body wall.

 Follow the dorsal aorta posteriorly and identify the following paired and unpaired branches. The celiac artery (trunk) gives off branches to the gonads, esophagus, and cardiac stomach before dividing into the gastrohepatic (which separates into gastric and hepatic arteries) and pancreaticomesenteric artery which supplies much of the anterior digestive tract and including the anterior intestinal artery. From the anterior intestinal artery you can observe the annular arteries supplying the spiral valve. Note the posterior intestinal artery and the gastrosplenic artery. Near the rectal gland, the posterior mesenteric artery arises from the aorta. Finally note the paired iliac arteries.

 The hepatic portal system of the shark consists of a large hepatic portal vein which receives blood from the gastric vein, the lienomesenteric vein, and the anterior intestinal vein.