This article seeks to review the homologous relationships in muscle phylogeny between the reptiles and primates (in particular, Homo sapiens), thereby analyzing the basis for morphological changes that could have occurred during the evolutionary process. One of the major challenges that have been encountered by various anatomists and biologists is having a uniformity in the homologous arrangement of muscles in vertebrate groups. This is to say that there are certain differences among authors in how they view the evolution of muscles among vertebrate species. The possible reason for this current challenge is that the position and attachment of these muscles change during evolution. For instance, the position and attachment of a muscle to the same bone or cartilage in one vertebrate may differ in origins from those of another vertebrate species. In examining the phylogenic relations in the head and neck regions, the muscle, intermandibularis posterior present in reptiles is homologous to the mylohyoideus and digastricus anterior muscles in primates (Jarvik, 1963 & 1980). All three muscles play a huge role in the opening of the jaw. Morphologically in reptiles, the intermandibularis posterior attaches to the Meckel’ss cartilage to the basihyal cartilage. In humans, the mylohyoideus muscle takes origin from the mylohyoid line of the inner mandible and inserting on the hyoid bone while the digastricus anterior muscle attaches to the digastric fossa on the base of the mandible. In Homo sapiens, both muscles are closely united anatomically as they share a common embryological origin, the first pharyngeal arch. The morphological orientation of the reptilian mandible had evolved to a more depressed form in primates, simultaneously causing the hyoid bone to change its shape from a less thinner, slightly V-shaped to a thicker, cortical H-shaped hyoid found in primates.