The gray substance of the medulla oblongata and trapezium.

The first American medical book illustrated with photomechanically reproduced plates. Oliver Wendell Holmes praised the book for its remarkable photomicrographs, which may be the first published of brain cross-sections. On pp. 66-69 Dean described his method of preparing specimens using a modified Clarke technique, and photographing with a common camera fitted with an adapter of his design to his Smith & Beck microscope.