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Like the cat, the shark's dye injection had gone amuck, leaving the coelomic cavity full of sticky blue goo. Unlike the cat, getting to the heart required several hours of chipping away at cartilage (which inevitably flies up and hits you in the face). By the time I'd isolated the blood vessels in both -- at least as much as I was ever going to -- I was already two weeks behind.

At first glance you'd think that a shark and a cat have little in common when it comes to blood circulation. Sure, they both have a heart and blood vessels (though, several of the shark's "veins" are actually large sack-like structures, not tubes), but there's a few obvious differences such as, oh idunno, gills maybe. As usual, evolution didn't bother to get rid of the old design and start cleanly. Instead, development is a messy affair in which the aortic arches that would have gone to gills instead get pruned off and rerouted and twisted and otherwise placed in confusing disarray. It's indescribably fascinating nonetheless.

One of the things I didn't know about the circulatory system was the complexity of the hepatic portal vessel. A portal vessel is a vein that's terminated at both ends by capillaries. You have a set of portal vessels that come out of your guts and wind up in your liver, so that the latter organ can take a crack at detoxifying whatever god-awful crap you just shovelled into your gullet. I'd assumed a simple vein from the intestines to the liver, but it actually drains everything from the stomach down to the colon, plus the pancreas and spleen. Whether that's functional, or just an artifact of development, I don't know.

The best thing I can say about learning the blood vessels is, draw them all out. It doesn't have to be artistic, but it does have to accurately reflect the way in which vessels connect together. From an artistic perspective, my drawings sucked. But that didn't really make any difference. The important part was I could say that after the coeliac, the next five branches off the aorta were the cranial mesenteric, cranial abdominal, renal, ovarian, and caudal mesenteric (roughly. Your mileage, and your cat, may vary). Some vessels are more easily learned by where they go or what landmarks they pass, others by their topology (what they branch from and in what order). Try both.

The fact that some shark and some cat vessels are almost named the same is enormously frustrating. Make sure you have both down. If you're doing Necturus, I'm sure it has confusingly-named vessels as well.