The Head Musculature of Heloderma

The helodermatidae are generally considered to represent primitive platynotan lizards (McDowell and Bogert, 1954). Their precise phylogenetic position is still subject of considerable controversy, however (c.f. Camp, 1923; Hoffstetter, 1962 a; Russell, 1967). So far, the structure of head muscles has not been used as a test of helodermatid relationships, although a number of workers have dealt with it (Shufeldt, 1890; Poglayen-Neuwall, 1954; Gomes, 1973). The throat musculature is known through the work of Camp (1923) and McDowell (1972), but here again additional details useful for comparative purposes could be found. Of the two species, only H. suspectum has been dissected so far (Haas, 1973). A comparison of H. suspectum with H. horridum provided very few dissimilarities, however.