A Guide for the Dissection of the Dogfish (Squalus Acanthias)

by Lawrence Edmonds Griffin

Venous system. All the blood of the body is conveyed to the sinus venosus. The sides of the sinus venosus are extended as large vessels, already referred to as the ducti cuvierii. Open the sinus and ducti by a transverse ventral incision. The ducti pass directly into the lateral veins. Near the middle of the posterior wall of the sinus is an aperture of varying size, the opening of the hepatic sinus; there are rarely two openings in Squalus, always two in Eugaleus. A large opening on the posterior wall of each ductus leads into the posterior cardinal vein. On the anterior wall of the ductus, near the sinus venosus, is a small aperture, that of the inferior jugular vein. Lateral to this is frequently a somewhat larger opening of the anterior cardinal vein. This is absent, however, in the majority of specimens; the anterior cardinals opening into the anterior ends of the posterior cardinals in about six out of ten cases.

A large cavity, the hepatic sinus, exists in the anterior end of the liver just posterior to the suspensory ligament. Cut into the liver at this point until the sinus is found, open it, and observe the large hepatic veins bringing blood into it from the liver, as well as its communication with the sinus venosus.

Trace all veins by passing a flexible probe or guarded bristle along them and then opening the vein with the probe as a guide. All smaller vessels emptying into those described should be noted.

The lateral veins pass forward to the posterior edge of the pectoral girdle, bend sharply dorsad, and enter the lateral extremities of the ducti cuvierii. Open a lateral vein near the anterior end and trace it toward the heart. The right and left lateral veins are joined by a vein passing along the ventral bar of the pectoral girdle. Open the lateral veins at a point about two inches in front of the pelvic girdle and trace the veins backward as far as they can be followed. The blood from the pelvic fins enters the lateral vein through the femoral vein. The lateral veins finally unite back of the cloaca.

Just before the lateral vein enters the ductus cuvierius it is joined by a large coracoid vein which runs dorsad and posteriorly along the posterior edge of the pectoral arch. Follow its course. It receives a good-sized pectoral vein from the pectoral fin, and sometimes several smaller veins from the same region. Traced dorsad it is found to open into a large blood sinus above the liver and oesophagus, the cardinal sinus.

In Eugaleus this connecting vein between the lateral vein and the cardinal sinus is wanting, the pectoral vein opening directly into the lateral.

The ventral cutaneous vein, which runs along the ventral midline of the body wall, should be followed; anteriorly it joins the vessel uniting the two laterals; posteriorly it divides at the pelvic arch and anastomoses with the laterals.

Pass a bristle from the sinus venosus into one of the posterior cardinal veins and trace the vein backward between the kidneys as far as possible. Open both posterior cardinals in this way, washing them out and observing that they receive blood from the kidneys by a series of renal veins, and that they are separate in their posterior parts, but communicate with each other anteriorly, where they are greatly expanded; the communicating portions and coincident enlargement forming the cardinal sinus. The anterior portion of the cardinal vein receives ovarian or spermatic veins from the female or male gonad, anterior oviducal veins from the anterior part of the oviduct, and segmental veins from the corresponding region of the body wall. There sometimes is more than a single opening from the posterior cardinal vein into the cuvierian duct.

Cut across the tail an inch behind the cloaca. Two vessels lie in the cartilaginous arch below the centra of the vertebrae; the dorsal of the two is the caudal artery, the ventral one is the caudal vein. Follow the vein forward. Dorsal to the cloaca it divides into two, which should be followed along the dorsal surfaces of the kidneys. These are the renal portal veins, conveying blood to the kidneys. Besides collecting the blood of the tail the renal portals also receive the posterior oviducal and segmental veins. They pass into the capillaries of the kidneys.

The inferior jugular vein opens into the medial end of the cuvierian duct. Trace it forward along the ventral ends of the gill pouches; it receives vessels from the arches and finally joins the hyoidean veins which follow the hyoid arch. At the outer end of the cuvierian duct there is often a small opening on the anterior wall opposite the mouth of the posterior cardinal vein. This leads into the anterior cardinal vein. As mentioned before, in a slight majority of the cases examined, the anterior cardinal vein opens into the posterior cardinal vein, not directly into the cuvierian duct. If possible, pass a bristle into the anterior cardinal. To follow the vein, and usually this is the best way to find it, make a vertical longitudinal incision upon the dorsal side of the neck, between the gill pouches and the mass of muscle lying beside the vertebral column. This will open the anterior cardinal, which is considerably expanded in this region, and it may be traced from this point toward the heart and the head. The anterior cardinal narrows suddenly in front of the anterior gill pouch, and leads downward to the orbit, where it expands into the orbital sinus surrounding the eyeball and its muscles. Trace the anterior cardinal only as far as the opening into the orbital sinus at this time. Veins from the anterior portion of the head and from the brain can be followed when the dissection of the eye is undertaken.