Fig. 8
From: Development of hypobranchial muscles with special reference to the evolution of the vertebrate neck
Evolution of the head–trunk interface and HBMs. Schematic representations of the vertebrate head–trunk interface (a, b). The pericardium is located ventral to the pharyngeal arches in crown gnathostomes (a), whereas the pericardium is posterior to the arches in the lamprey (b). Dotted lines indicate the head–trunk interface. c A phylogenetic tree (modified from [63, 68]) with lateral and anterior views of HBMs and pharyngeal arches in crown gnathostomes (left) and the lamprey (right). Arrowheads indicate HBMs. Putative HBMs are shown in red lines in placoderm [67]. b, branchial arch; h, hyoid arch; m, mandibular arch; p, pharyngeal arches; pcm, pericardial mesoderm