In the foregoing, all of the muscles of the head and the branchial region, with the exception of the eye muscles, have been considered. The two forms studied agree very closely when their difference in shape is considered. In the skate, as might be expected from its extreme modification, a few muscles are developed which are not found in the dogfish. These are the levator and depressor of the rostrum, and the cerato-hyomandibularis which, from its position, seems adapted to the protrusion of the jaws.The muscles of the skate referred to by Tiessing as "Csvp3-5," are here interpreted as fibers of the interbranchials which have acquired an extreme development. The muscles in Acanthias, marked Csv 2 and Csβ 2 by Vetter, are here regarded as the first and second ventral constrictors respectively. The deeper ventral longitudinal muscles of Raia are described for the first time.