How is the field of anatomy divided into subdivisions?

The field of anatomy is generally divided into macroscopic, or gross anatomy (not requiring a microscope), and microscopic anatomy. Gross anatomy includes the  subdivisions of regional anatomy, systemic anatomy, developmental anatomy, and clinical an­­­­­atomy. Regional anatomy studies specific regions of the body, such as the head and neck or lower and upper limbs. Systemic anatomy studies different body systems, such as the digestive system and reproductive system. Developmental anatomy describes the changes that occur from conception through physical maturity. Clinical anatomy includes medical anatomy (anatomical features that change during illness) and radiographic anatomy (anatomical structures seen using various imaging techniques). 

The two major subdivisions of microscopic anatomy are cytology and histology. Cytology (from the Greek cyto, meaning “cell”) is the study and analysis of the  internal structure of individual cells. Histology (from the Greek histos, meaning “web”) is the study and examination of tissues.