I recently stumbled upon an e book recommended by someone in the voice acting community:
The Hygiene of the vocal organs: A Practical Handbook for Singers and Speakers
By Morell Mackenzie – Published 1886
This is one of the gems found in Google’s digital e-books library. This handbook, despite the sometimes odd approach to descriptions, contains a vast amount of detail.
A great deal of the book’s opening sections deal with anatomy. There is also discussion on the need for constant practice, the breaking voice, avoidance of strain, and suggestions on care of the voice- all as valid today as when written over 200 years ago!
It can be downloaded as a pdf or you can look it up through Google Book search and view it as html.