The neural crest is a transient embryonic structure unique to vertebrates. Cells migrate away from the neural crest during embryogenesis and give rise to many different cell types in a large variety of tissues and organs (for two recent book-length reviews see Hall, 1999 and LeDouarin and Kalcheim, 1999). In the head, unlike in the trunk, neural crest cells give rise to skeletal and dental tissues. In the chicken embryo, the migration and fate of cranial neural crest cells has been investigated very thoroughly, and it has been shown that most of the skull is neural crest derived. Data from other vertebrates indicate that this finding is a general vertebrate trait (Schilling, 1997; Osumi-Yamashita et al., 1997; Horigome et al., 1999; Manzanares et al., 2000; Kimmel et al., 2001). A direct contribution of neural crest cells to cranial musculature was first reported in 1975 by LeDouarin's group (LeLièvre and LeDouarin, 1975), and later confirmed by Noden (1983a, b) and Couly et al. (1992), who described the crest derivation of connective tissue components of several visceral arch muscles in quail–chick chimeras. More recent work has revealed that this additional role of the neural crest is only one component of a much more comprehensive mechanism of cranial development and patterning, in which positional relations among hindbrain segments (rhombomeres), the neural crest, and musculoskeletal derivatives are maintained throughout crest migration, pattern formation, and histogenesis (Graham et al., 1996; Köntges and Lumsden, 1996; Schilling, 1997; Schilling and Kimmel, 1997). The known complexity of cranial development increased even further with the discovery that the foregut endoderm is responsible for patterning the cartilages of the visceral arches (Couly et al., 2002; Ruhin et al., 2003, but first indications already in Hörstadius and Sellman, 1946). Several fate maps in chicken and mouse have shown that the myogenic cells originate from the paraxial mesoderm (Noden, 1983a, 1986; Couly et al., 1992; Trainor et al., 1994; Trainor and Tam, 1995; Hacker and Guthrie, 1998). Unlike in the trunk, the paraxial mesoderm in the head is not obviously segmented (Kuratani et al., 1999; Noden et al., 1999; Jouve et al., 2002, but see Jacobson, 1988). However, mesodermal and neural crest contributions to a visceral arch originate from approximately the same axial level (Noden, 1986; Couly et al., 1992; Schilling and Kimmel, 1994; Trainor et al., 1994; Trainor and Tam, 1995; Hacker and Guthrie, 1998). As most of the bones and cartilages in the head are neural crest-derived, the main contribution of the mesoderm is to muscles and blood vessels. Only a few studies have examined the relationship between cranial muscles and the cranial neural crest. Although several studies have included extirpations of neural crest cells, only a few have investigated the impact on cranial muscle development. Piatt (1938) included some comments on muscle development, and E.K. Hall showed (Hall, 1950) that the cranial muscles develop but are distorted when neural folds have been removed. The most recent study is that by Olsson et al. (2001) of the anuran Bombina orientalis. They performed extirpations when the neural crest cells had already started migrating, using the dark appearance of the neural crest cells. The results showed that cranial muscles were severely affected. The muscles seemed distorted and had often anastomosed with each other. Olsson and coworkers concluded that neural crest cells are crucial for correct morphogenesis of the visceral arch muscles. However, despite extirpations, muscles seem to appear more or less in their normal positions. The fate of the cranial neural crest cells is relatively unknown from a comparative perspective. With the exception of the chick–quail chimera technique, data are mostly derived from extirpations or vital dye experiments, including several classic studies on amphibians (Hall and Hörstadius, 1988). A direct contribution of the cranial neural crest to connective tissues in cranial muscles in amphibians, however, was not reported until 1987, when Sadaghiani and Thiébaud published results from chimeric Xenopus larvae. In analogy with the chick–quail studies, they had grafted neural fold material from Xenopus borealis into Xenopus laevis and used the fact that the nuclei could be distinguished between the species to undertake a fate mapping. They observed neural crest-derived cells in several cranial muscles (Sadaghiani and Thiébaud, 1987). Later, Olsson and coworkers, using extirpations and DiI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine, perchlorate) injections in the frog Bombina orientalis, concluded that there is a neural crest contribution to the connective-tissue component but not the myofibers of many larval muscles within the first two (mandibular and hyoid) branchial arches (Olsson et al., 2001). However, despite some preliminary data (Olsson et al., 2000), whether this finding is also true for salamanders has remained unclear. The aims of this study were to investigate the role of cranial neural crest cells in the formation of visceral arch muscles in the Mexican axolotl, and to see whether a role in muscle morphogenesis could be explained by the presence of neural crest cells in the connective tissues surrounding cranial muscles, as has been reported for other species (Noden, 1983b; Sadaghiani and Thiébaud, 1987; Köntges and Lumsden, 1996; Olsson et al., 2001). We found DiI-labeled cells in connective tissue surrounding muscle fibers and also between the muscle anlagen and the anlagen of the cartilages. The extirpation experiments showed that visceral arch muscles formed close to their origin in the absence of neural crest cells but failed to extend toward their normal insertions. We conclude that the cranial neural crest is not important for the correct early positioning of cranial muscles but is crucial for achieving the correct morphology. We interpret the complicated disturbances to muscle development induced by extirpations of each of the streams of cranial neural crest cells to be owing to the lack of directional guidance provided by neural crest derived connective tissues surrounding the myofibers.