When I’m teaching, I frequently find myself caught between a fascinating digression and the need to keep things simple. For example, if I’m teaching my Human Anatomy class about the lower jaw, I always have to fight an urge to launch into the complexities of lower jaw evolution.
“See? This is the mandible,” I say, “and it’s just one piece of bone.” But all the while, I am clamping my teeth down firmly on my tongue because the exciting truth is that the human mandible isn’t just one bone: it’s really composed of two symmetrical bones, which are called the “dentaries” and are fused together at the midline, but most other mammals have unfused dentaries, and in fact all other vertebrate classes (and the ancestors of all mammals!) have a mandible that is composed of several bones, which include the dentary, the angular, the surrangular and…
You see how it is? The paired dentary thing might be a bit interesting to my pre-nursing students, because human fetuses have that condition. But they could care less about the number of bones in the mouth of a carp and which of those elements are retained by toads and snakes.
At least, not if it isn’t on the test. Continue reading