The _premaxillae_ (fig. 11, 20), the largest of these, overlaps the maxilla behind; both bones bear teeth. The _jugal_ (fig. 11, 17) lies above the maxilla and overlaps it in front. THE LOWER JAW. The =lower jaw= is a strong bar and is like the upper jaw, partly cartilaginous, forming =Meckel's cartilage=, partly ossified, and sheathed to a considerable extent in membrane bone. The outer side and posterior end is ossified, forming the large =articular= (fig. 11, 21), but the condyle is cartilaginous and the anterior part of the articular forms merely a splint on the outer side of Meckel's cartilage, which extends beyond it for a considerable distance. The angle of the jaw just below the condyle is formed by a small _angular_ (fig. 11, 22), and the anterior two-thirds of the jaw is sheathed in the large tooth-bearing _dentary_ (fig. 11, 23). THE HYOID ARCH. The =hyoid arch= has a number of ossifications in it and is closely connected with the mandibular arch. The =hyomandibular= (fig. 11, 24) is a large bone which articulates with a shallow groove lined by cartilage and formed partly in the pterotic, partly in front of it. The hyomandibular is overlapped in front by the meta-pterygoid, while below it tapers and is succeeded by a small area of unossified cartilage followed by the forwardly directed =symplectic= which fits into a groove in the quadrate. The unossified tract between the hyomandibular and symplectic is continuous in front with a strong bar, which remains partly cartilaginous and is partly converted into cartilage bone. The proximal part is ossified, forming the =epi-hyal=, the middle part forms the =cerato-hyal= (fig. 11, 27), in front of which is the small =hypo-hyal=. The hyoid arches of the two sides are united by the large tooth-bearing =glosso-hyal= (fig. 11, 29). Attached to the lower surface of the hyoid arch are a series of twelve flat _branchiostegal rays_ (fig. 11, 35). Each overlaps the one in front of it, the posterior one being the largest. The branchiostegal rays of the two sides are united in front by an unpaired membrane bone, the _basi-branchiostegal_ (fig. 11, 36). =Opercular bones.= Behind the hyomandibular there is a large bony plate, the =operculum=, formed of four large membrane bones. The anterior of these, the _pre-opercular_ (fig. 11, 33), is crescentic in shape, and with its upper end a small _supratemporal_ (fig. 11, 34) is connected. Behind the upper part of the pre-opercular is the largest of the opercular bones, the _opercular proper_. Its lower edge overlaps the sub-opercular, and both opercular and sub-opercular are overlapped by the _infra-opercular_ (fig. 11, 32) in front. The infra-opercular is in its turn overlapped by the _pre-opercular_. BRANCHIAL ARCHES.