**1. Introduction**

The rhesus monkey (*Macaca mulatta*) belongs to the class of the mammals (*Mammalia*), the order of the primates (*Primates*), the family of the Old World monkeys (*Cercopithecidae*) and the genus *Macaca*. This animal finds its origin in the southern parts of Asia but is widespread throughout the world as one of the most frequently used laboratory animal. This is the result of the many similarities between the rhesus monkey and humans. Both species have common ancestry with genomes that are identical for 93.5% [1]. Only great apes present a larger degree of similarity with humans, but their use in research is very strictly regulated [2].

Rhesus monkeys are commonly used in toxicity studies and play a pivotal role in unraveling the mechanisms of health and diseases and during the development of

vaccines. HIV, SARS and Covid-19 are a few examples of viral diseases that are studied in the rhesus monkey. In addition to investigations that require that the physiology of this laboratory animal parallels that of man, studies that demand a comparable anatomy are multiple as well. Examples include studies on osteoporosis, osteopenia, lordosis and kyphosis [1].

The aim of this book chapter is to provide the biomedical researcher, who studies and/or uses the rhesus monkey, with the essentials of its anatomy. Although this chapter is rather elaborate, not all the details of the rhesus monkey anatomy can be described. Where appropriate, emphasis is put on those structures that have importance during manipulations of the animal under investigation, such as the muscles that allow for intramuscular injection and the veins that can be punctured to draw blood or inject substances intravenously. Researchers can be referred to two anatomical atlases for further reading. These include the work by Hartman and Straus Jr. from 1933, entitled *The Anatomy of the Rhesus Monkey (*Macaca mulatta*)* [3] and the work by Berringer and coworkers from 1968, entitled *An Atlas and Dissection Manual of Rhesus Monkey Anatomy* [4]. However, these reference works are outdated as they present black-and-white photographs and line drawings to visualize the anatomy. In addition, they make use of human terminology that is often archaic. In the present book chapter, more than 70 full color photographs are shown. In the figure legends, the official veterinary anatomical nomenclature is used [5]. In the text, however, English terms are used to enhance the readability. All materials for this study were obtained from animals that were euthanized for ethical reasons. No animals were euthanized for the purpose of this chapter.
