Slide 1203 will give you an opportunity to examine the structure of sinus hairs.  These are extremely large hairs, with large blood filled sinuses surrounding their bases. Ifyou examine the head of a dog, you'll see that he has vibrissae on the sides, top, and bottom of his head.  These serve the same function as curb feelers on a car, i.e., they alert the animalwhen he is close to an edge.

This theoretically helps the dog to keep from getting his head stuck in a bucket or a hollow tree. (I must say that most dogs I've known have blithely ignored the signals, at least once in their lifetime.)

Actually, all hairs have fine nerve fibers which invest the base of the follicle, and serve as tactile sensors. If you don't believe this, pull one out of your arm.