(Chapter 15) Footnote 27:

This sentence was moved to the end of the preceding section in the 1555 edition. It should be noted that all mammals, with the exception of a few endentates and the manatee, have seven cervical vertebrae. In birds, the number of cervical vertebrae is variable, with the greatest number in birds with long necks; the pigeon, for example, has fourteen cervical vertebrae.