The =lower jaw or mandible= like that of the Salmon is partly cartilaginous, forming =Meckel's cartilage=, partly formed of cartilage bone, partly of membrane bone. Meckel's cartilage is of course not seen in the dried skull. The lower jaw includes one cartilage bone, the =articular= (fig. 12, 9), this is a large bone connected by a saddle-shaped surface with the quadrate. Meckel's cartilage lies in a groove on its under surface, and projects beyond it in front. The _angular_ is a small thick bone united to the lower surface of the articular at its posterior end. The _dentary_ (fig. 12, 10) is a large tooth-bearing bone meeting its fellow in the middle line in front, while the articular fits into a deep notch at its posterior end. THE HYOID ARCH. The =hyomandibular= (fig. 12, 7) is a large irregular bone, articulating by a prominent rounded head with the sphenotic and pterotic. It is united in front with the meta-pterygoid and symplectic, and sends off behind a strong process which articulates with the opercular. The =symplectic= is a long somewhat triangular bone drawn out in front into a process which fits into a groove on the inner surface of the quadrate. The distal portion of the hyoid arch is strongly developed and consists of first the =inter-hyal= (fig. 12, 11), a short bony rod, which articulates dorsally with a patch of cartilage intervening between the posterior part of the hyomandibular and the symplectic. Below it is united with the apex of the triangular =epi-hyal=, a bone suturally connected with the large =cerato-hyal= (fig. 12, 13) which unites distally with two small =hypo-hyals=. To the cerato-hyal are attached a series of seven strong curved cylindrical rods, the _branchiostegal rays_. The first of these is the smallest and they increase in size up to the last. The four dorsal ones are attached to the outer surface of the cerato-hyal, the three ventral ones to its inner surface. Interposed between the hypo-hyals of the two sides is an unpaired somewhat triangular plate, the uro-hyal or _basi-branchiostegal_ (fig. 12, 15). THE BRANCHIAL ARCHES. The =branchial arches= are five in number and consist of the following parts on each side. The dorsal end is formed of the =supra-pharyngeal= bone, a large irregular bone covered ventrally with teeth of a fair size, and representing the fused =pharyngo-branchials= of the four anterior arches. Its external surface is continuous with four small =epi-branchials= which pass horizontally backwards and outwards. Their distal ends meet four long =cerato-branchials= which are directed forwards and inwards and form the principal part of the arches.