I thought I already had a head?

I found the dissection of the human heads kind of gruesome. The brutal language such as "crushing" and "sawed" gave me the similar feeling of "the willies". In relation to fish, however, Shubin describes how humans use their heads to control bodily functions such as moving of the eyes and smelling; two functions that fish don't seem to have. Fish do not blink or have the overlapping vision like humans but apparently still have the same head structure as humans'. As he continues on about the different nerves and such, Shubin attempts to relate it to wires and other technical things, which I find unnecessary.

When Shubin began to discuss the different arches of the facial structures, I became extremely confused. The development of an human embryo and a shark embryo are similar yet produce two entirely different species. I was surprised to find how close each arch resembled the other in the early stages of embryonic development. After the basic animal's structure was developed I didn't understand the gills part of the chapter and how it relates to humans. Although sharks and humans share the arches what causes the gills to form versus lungs and even as adults do we still share the arches or do they differ just like their physical appearances. From headless to headed and embryo to adult, do nerves/arches truly show a resemblance or is it just a necessity for all living creatures even prehistoric one? I'm fully interested in this, at first thought boring, documentary on my inner fish.