MUSCULATURE OF THE HEAD AND NECK. On the lateral and ventral surfaces of the neck the primary relations of the myomeres are much modified by the development of numerous special muscles, yet here and there traces of the metameric arrangement still show. Immediately beneath the skin is a thin sheet of muscle covering most of the ventral and lateral surfaces of the throat as far back as the pectoral girdle. On the ventral surface a triangular space is left in front of the pectoral bar; on the sides of the neck the sheet extends back to the last gill-cleft; dorsally, it reaches to the upper extremities of the gill pouches. This is the _constrictor superficialis_ muscle. It is attached to fasciae dorsally and ventrally, and to the extra-branchial cartilages. The constrictor superficialis consists of six metameric segments. The four posterior ones are distinctly limited by the gill-slits and extra-branchial cartilages. The second is anterior to the first gill slit, the largest of all, with distinct dorsal and ventral portions extending forward above and below the jaws. The first is recognized as consisting of two distinct parts, on the dorsal and ventral surfaces of the head. The dorsal portion is a small curved muscle on the anterior wall of the spiracle, extending from the external surface of the auditory capsule to the inner surface of the lower jaw. It lies close against the levator marillae superioris (see below). On the ventral surface of the throat the posterior constrictor muscles of the two sides are separated by a large triangular area. In front of this the ventral portions of the first and second constrictors meet in a median aponeurosis, from which their fibres extend transversely, those of the first to the mandibular cartilage, those of the second to the hyoidean cartilage. The first constrictor lies ventral or superficially to, and largely covers the second. Reflect the first constrictor from the aponeurosis outward, and demonstrate the two layers of muscle. It will be noted that the second to sixth constrictors consist of united dorsal, lateral and ventral portions, while the first is reduced to widely separated dorsal and ventral parts. On each side of the head, just outside the angle of the mouth, is a large, thick muscle arising from the lateral surface of the cranium, and inserted upon the outer surface of the mandible, the _adductor mandibularis_. In front of the small dorsal constrictor superficialis 1, and scarcely separated from it, is the strong _levator maxillae superioris_, which extends from the lateral surface of the auditory capsule to the dorsal edge of the palato-quadrate cartilage.