I have listed below optional dissection guides you can order to supplement the instructions in the Blood and Guts book. Here are my thoughts about the guides (thanks Wanda for asking about this!):

 You don’t HAVE to use the dissection guides if you your dissections to be very low key. The Blood and Guts book tells you the major things you should do with the items and points out certain structures. For example, with the dissection of the heart, the Blood and Guts books says something like, “Slice the heart in half to see the inside. Cut slowly. Notice how things are attached before you cut them…See if you can find the four chambers, the valves and the main arteries.” Besides some additional, simple instructions, there is an illustration showing the main things to try and find.
The Nasco guides you can get from Home Science Tools just go more in depth. They list more of the structures and give a more detailed instructions.
I figured that for the age group Otter’s Science is intended for, the Blood and Guts book is enough instruction. The idea is just to let them explore, learn a few of the structures and see how things are put together. A child could easily read the Blood and Guts book and with some supervision even make all of the cuts, etc. and actually understand the instructions.
I included the guides for the high school study because I figured older kids would need more depth. The NASCO guides also use a higher vocabulary like: “ With a fine pointed scissors, cut a tangential slice from the lateral surface of the eye…” If you use the guides, you will have to probably have to lead the dissection because the instructions are most likely too difficult for younger kids to follow themselves.
I’m just going to use the Blood and Guts book with Otter and then Bear will use the guides. Otter is 10 and I want him to just enjoy exploring the organs. He can always do more in depth dissections later in high school biology.

Here are the guides, if you would like them:

Sheep Brain Dissection booklet

Animal Heart Dissection guide

Sheep Kidney Dissection guide

Dissection tools These are totally optional as well - The Blood and Guts books shows household cutting tools being used.