Anatomy is the science of the shape and structure of organisms and their parts; dissection of dead material is employed to provide information on the gross structure. Early anatomists recognized that an animal’s body is made up of different types of tissue, and with the development of the light microscope, histology – the science of tissues – became a new field of study. The new science expanded further when varieties of dyes able to stain dissected material specifically were developed. It became evident that only four basic tissues are present: epithelium, connective tissue, muscle tissue and nervous tissue. All the various parts of the body are derived from these components, and the distinctive appearance of gross anatomical structures depends on which type of tissue is predominant. Each tissue is an assemblage of cells and their derivatives. The balance of cells of different types and these derivatives, and the combination of the different tissues give each part of the body a definitive appearance that can be identified microscopically.