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.